os_win_c.cs

#define SQLITE_OS_WIN

using System;
using System.Diagnostics;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.Versioning;
using System.Text;
using System.Threading;
using DWORD = System.UInt64;
using HANDLE = System.IntPtr;
using i64 = System.Int64;
using sqlite3_int64 = System.Int64;
using u32 = System.UInt32;
using u8 = System.Byte;
#if SQLITE_WINRT
using System.Threading.Tasks;
using Windows.Storage;
using Windows.Storage.Streams;
using System.Runtime.InteropServices.WindowsRuntime;
#elif WINDOWS_PHONE || SQLITE_SILVERLIGHT  
using System.IO.IsolatedStorage;
#endif
#if !FEATURE_RUNTIMEINFORMATION
using IronPython;
#endif
namespace Community.CsharpSqlite
{
  public partial class Sqlite3
  {
    /*
    ** 2004 May 22
    **
    ** The author disclaims copyright to this source code.  In place of
    ** a legal notice, here is a blessing:
    **
    **    May you do good and not evil.
    **    May you find forgiveness for yourself and forgive others.
    **    May you share freely, never taking more than you give.
    **
    ******************************************************************************
    **
    ** This file contains code that is specific to windows.
    *************************************************************************
    **  Included in SQLite3 port to C#-SQLite;  2008 Noah B Hart
    **  C#-SQLite is an independent reimplementation of the SQLite software library
    **
    **  SQLITE_SOURCE_ID: 2011-06-23 19:49:22 4374b7e83ea0a3fbc3691f9c0c936272862f32f2
    **
    *************************************************************************
    */
    //#include "sqliteInt.h"
#if SQLITE_OS_WIN               // * This file is used for windows only */

    /*
** A Note About Memory Allocation:
**
** This driver uses malloc()/free() directly rather than going through
** the SQLite-wrappers sqlite3Malloc()/sqlite3DbFree(db,ref  ).  Those wrappers
** are designed for use on embedded systems where memory is scarce and
** malloc failures happen frequently.  Win32 does not typically run on
** embedded systems, and when it does the developers normally have bigger
** problems to worry about than running out of memory.  So there is not
** a compelling need to use the wrappers.
**
** But there is a good reason to not use the wrappers.  If we use the
** wrappers then we will get simulated malloc() failures within this
** driver.  And that causes all kinds of problems for our tests.  We
** could enhance SQLite to deal with simulated malloc failures within
** the OS driver, but the code to deal with those failure would not
** be exercised on Linux (which does not need to malloc() in the driver)
** and so we would have difficulty writing coverage tests for that
** code.  Better to leave the code out, we think.
**
** The point of this discussion is as follows:  When creating a new
** OS layer for an embedded system, if you use this file as an example,
** avoid the use of malloc()/free().  Those routines work ok on windows
** desktops but not so well in embedded systems.
*/

    //#include <winbase.h>

#if __CYGWIN__
//# include <sys/cygwin.h>
#endif

    /*
** Macros used to determine whether or not to use threads.
*/
#if THREADSAFE
//# define SQLITE_W32_THREADS 1
#endif

    /*
** Include code that is common to all os_*.c files
*/
    //#include "os_common.h"

    /*
    ** Some microsoft compilers lack this definition.
    */
#if !INVALID_FILE_ATTRIBUTES
    //# define INVALID_FILE_ATTRIBUTES ((DWORD)-1)
    const int INVALID_FILE_ATTRIBUTES = -1;
#endif

    /*
** Determine if we are dealing with WindowsCE - which has a much
** reduced API.
*/
#if SQLITE_OS_WINCE
//# define AreFileApisANSI() 1
//# define GetDiskFreeSpaceW() 0
#endif

    /* Forward references */
    //typedef struct winShm winShm;           /* A connection to shared-memory */
    //typedef struct winShmNode winShmNode;   /* A region of shared-memory */

    /*
    ** WinCE lacks native support for file locking so we have to fake it
    ** with some code of our own.
    */
#if SQLITE_OS_WINCE
typedef struct winceLock {
int nReaders;       /* Number of reader locks obtained */
BOOL bPending;      /* Indicates a pending lock has been obtained */
BOOL bReserved;     /* Indicates a reserved lock has been obtained */
BOOL bExclusive;    /* Indicates an exclusive lock has been obtained */
} winceLock;
#endif

    private static LockingStrategy lockingStrategy = HelperMethods.IsRunningMediumTrust() ? new MediumTrustLockingStrategy() : new LockingStrategy();

    /*
    ** The winFile structure is a subclass of sqlite3_file* specific to the win32
    ** portability layer.
    */
    //typedef struct sqlite3_file sqlite3_file;
    public partial class sqlite3_file
    {
      public sqlite3_vfs pVfs;       /* The VFS used to open this file */
#if SQLITE_WINRT
      public IRandomAccessStream fs;
#else
      public FileStream fs;          /* Filestream access to this file*/
#endif
      // public HANDLE h;            /* Handle for accessing the file */
      public int locktype;           /* Type of lock currently held on this file */
      public int sharedLockByte;     /* Randomly chosen byte used as a shared lock */
      public DWORD lastErrno;        /* The Windows errno from the last I/O error */
      public DWORD sectorSize;       /* Sector size of the device file is on */
#if !SQLITE_OMIT_WAL
public winShm pShm;            /* Instance of shared memory on this file */
#else
      public object pShm;            /* DUMMY Instance of shared memory on this file */
#endif
      public string zPath;           /* Full pathname of this file */
      public int szChunk;            /* Chunk size configured by FCNTL_CHUNK_SIZE */
#if SQLITE_OS_WINCE
Wstring zDeleteOnClose;  /* Name of file to delete when closing */
HANDLE hMutex;          /* Mutex used to control access to shared lock */
HANDLE hShared;         /* Shared memory segment used for locking */
winceLock local;        /* Locks obtained by this instance of sqlite3_file */
winceLock *shared;      /* Global shared lock memory for the file  */
#endif

      public void Clear()
      {
        pMethods = null;
        fs = null;
        locktype = 0;
        sharedLockByte = 0;
        lastErrno = 0;
        sectorSize = 0;
      }
    };

    /*
    ** Forward prototypes.
    */
    //static int getSectorSize(
    //    sqlite3_vfs *pVfs,
    //    string zRelative     /* UTF-8 file name */
    //);

    /*
    ** The following variable is (normally) set once and never changes
    ** thereafter.  It records whether the operating system is Win95
    ** or WinNT.
    **
    ** 0:   Operating system unknown.
    ** 1:   Operating system is Win95.
    ** 2:   Operating system is WinNT.
    **
    ** In order to facilitate testing on a WinNT system, the test fixture
    ** can manually set this value to 1 to emulate Win98 behavior.
    */
#if SQLITE_TEST
    int sqlite3_os_type = 0;
#else
static int sqlite3_os_type = 0;
#endif

    /*
** Return true (non-zero) if we are running under WinNT, Win2K, WinXP,
** or WinCE.  Return false (zero) for Win95, Win98, or WinME.
**
** Here is an interesting observation:  Win95, Win98, and WinME lack
** the LockFileEx() API.  But we can still statically link against that
** API as long as we don't call it when running Win95/98/ME.  A call to
** this routine is used to determine if the host is Win95/98/ME or
** WinNT/2K/XP so that we will know whether or not we can safely call
** the LockFileEx() API.
*/
#if SQLITE_OS_WINCE
//# define isNT()  (1)
#elif SQLITE_WINRT
    static bool isNT() { return true; }
#else
    static bool isNT()
    {
      //if (sqlite3_os_type == 0)
      //{
      //  OSVERSIONINFO sInfo;
      //  sInfo.dwOSVersionInfoSize = sInfo.Length;
      //  GetVersionEx(&sInfo);
      //  sqlite3_os_type = sInfo.dwPlatformId == VER_PLATFORM_WIN32_NT ? 2 : 1;
      //}
      //return sqlite3_os_type == 2;
      return Environment.OSVersion.Platform == PlatformID.Win32NT || Environment.OSVersion.Platform == PlatformID.Unix;
    }
#endif // * SQLITE_OS_WINCE */

    /*
** Convert a UTF-8 string to microsoft unicode (UTF-16?).
**
** Space to hold the returned string is obtained from malloc.
*/
    //static WCHAR *utf8ToUnicode(string zFilename){
    //  int nChar;
    //  Wstring zWideFilename;

    //  nChar = MultiByteToWideChar(CP_UTF8, 0, zFilename, -1, NULL, 0);
    //  zWideFilename = malloc( nChar*sizeof(zWideFilename[0]) );
    //  if( zWideFilename==0 ){
    //    return 0;
    //  }
    //  nChar = MultiByteToWideChar(CP_UTF8, 0, zFilename, -1, zWideFilename, nChar);
    //  if( nChar==0 ){
    //    free(zWideFilename);
    //    zWideFileName = "";
    //  }
    //  return zWideFilename;
    //}

    /*
    ** Convert microsoft unicode to UTF-8.  Space to hold the returned string is
    ** obtained from malloc().
    */
    //static char *unicodeToUtf8(const Wstring zWideFilename){
    //  int nByte;
    //  string zFilename;

    //  nByte = WideCharToMultiByte(CP_UTF8, 0, zWideFilename, -1, 0, 0, 0, 0);
    //  zFilename = malloc( nByte );
    //  if( zFilename==0 ){
    //    return 0;
    //  }
    //  nByte = WideCharToMultiByte(CP_UTF8, 0, zWideFilename, -1, zFilename, nByte,
    //                              0, 0);
    //  if( nByte == 0 ){
    //    free(zFilename);
    //    zFileName = "";
    //  }
    //  return zFilename;
    //}

    /*
    ** Convert an ansi string to microsoft unicode, based on the
    ** current codepage settings for file apis.
    **
    ** Space to hold the returned string is obtained
    ** from malloc.
    */
    //static WCHAR *mbcsToUnicode(string zFilename){
    //  int nByte;
    //  Wstring zMbcsFilename;
    //  int codepage = AreFileApisANSI() ? CP_ACP : CP_OEMCP;

    //  nByte = MultiByteToWideChar(codepage, 0, zFilename, -1, NULL,0)*WCHAR.Length;
    //  zMbcsFilename = malloc( nByte*sizeof(zMbcsFilename[0]) );
    //  if( zMbcsFilename==0 ){
    //    return 0;
    //  }
    //  nByte = MultiByteToWideChar(codepage, 0, zFilename, -1, zMbcsFilename, nByte);
    //  if( nByte==0 ){
    //    free(zMbcsFilename);
    //    zMbcsFileName = "";
    //  }
    //  return zMbcsFilename;
    //}

    /*
    ** Convert microsoft unicode to multibyte character string, based on the
    ** user's Ansi codepage.
    **
    ** Space to hold the returned string is obtained from
    ** malloc().
    */
    //static char *unicodeToMbcs(const Wstring zWideFilename){
    //  int nByte;
    //  string zFilename;
    //  int codepage = AreFileApisANSI() ? CP_ACP : CP_OEMCP;

    //  nByte = WideCharToMultiByte(codepage, 0, zWideFilename, -1, 0, 0, 0, 0);
    //  zFilename = malloc( nByte );
    //  if( zFilename==0 ){
    //    return 0;
    //  }
    //  nByte = WideCharToMultiByte(codepage, 0, zWideFilename, -1, zFilename, nByte,
    //                              0, 0);
    //  if( nByte == 0 ){
    //    free(zFilename);
    //    zFileName = "";
    //  }
    //  return zFilename;
    //}

    /*
    ** Convert multibyte character string to UTF-8.  Space to hold the
    ** returned string is obtained from malloc().
    */
    //static char *sqlite3_win32_mbcs_to_utf8(string zFilename){
    //  string zFilenameUtf8;
    //  Wstring zTmpWide;

    //  zTmpWide = mbcsToUnicode(zFilename);
    //  if( zTmpWide==0 ){
    //    return 0;
    //  }
    //  zFilenameUtf8 = unicodeToUtf8(zTmpWide);
    //  free(zTmpWide);
    //  return zFilenameUtf8;
    //}

    /*
    ** Convert UTF-8 to multibyte character string.  Space to hold the
    ** returned string is obtained from malloc().
    */
    //char *sqlite3_win32_utf8_to_mbcs(string zFilename){
    //  string zFilenameMbcs;
    //  Wstring zTmpWide;

    //  zTmpWide = utf8ToUnicode(zFilename);
    //  if( zTmpWide==0 ){
    //    return 0;
    //  }
    //  zFilenameMbcs = unicodeToMbcs(zTmpWide);
    //  free(zTmpWide);
    //  return zFilenameMbcs;
    //}

/*
** The return value of getLastErrorMsg
** is zero if the error message fits in the buffer, or non-zero
** otherwise (if the message was truncated).
*/
static int getLastErrorMsg(int nBuf, ref string zBuf){
  /* FormatMessage returns 0 on failure.  Otherwise it
  ** returns the number of TCHARs written to the output
  ** buffer, excluding the terminating null char.
  */
  //DWORD error = GetLastError();
  //DWORD dwLen = 0;
  //string zOut = "";

  //if( isNT() ){
    //Wstring zTempWide = NULL;
    //dwLen = FormatMessageW(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
    //                       NULL,
    //                       error,
    //                       0,
    //                       (LPWSTR) &zTempWide,
    //                       0,
    //                       0);
        zBuf = HelperMethods.GetLastError().ToString();//new Win32Exception( Marshal.GetLastWin32Error() ).Message;

    //if( dwLen > 0 ){
    //  /* allocate a buffer and convert to UTF8 */
    //  zOut = unicodeToUtf8(zTempWide);
    //  /* free the system buffer allocated by FormatMessage */
    //  LocalFree(zTempWide);
    //}
/* isNT() is 1 if SQLITE_OS_WINCE==1, so this else is never executed. 
** Since the ASCII version of these Windows API do not exist for WINCE,
** it's important to not reference them for WINCE builds.
*/
//#if !SQLITE_OS_WINCE //==0
//  }else{
//    string zTemp = null;
//    dwLen = FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
//                           null,
//                           error,
//                           0,
//                           ref zTemp,
//                           0,
//                           0);
//    if( dwLen > 0 ){
//      /* allocate a buffer and convert to UTF8 */
//      zOut = sqlite3_win32_mbcs_to_utf8(zTemp);
//      /* free the system buffer allocated by FormatMessage */
//      LocalFree(zTemp);
//    }
//#endif
//  }
  //if( 0 == dwLen ){
  //  sqlite3_snprintf(nBuf, zBuf, "OsError 0x%x (%u)", error, error);
  //}else{
  //  /* copy a maximum of nBuf chars to output buffer */
  //  sqlite3_snprintf(nBuf, zBuf, "%s", zOut);
  //  /* free the UTF8 buffer */
  //  free(zOut);
  //}
  return 0;
}

/*
**
** This function - winLogErrorAtLine() - is only ever called via the macro
** winLogError().
**
** This routine is invoked after an error occurs in an OS function.
** It logs a message using sqlite3_log() containing the current value of
** error code and, if possible, the human-readable equivalent from 
** FormatMessage.
**
** The first argument passed to the macro should be the error code that
** will be returned to SQLite (e.g. SQLITE_IOERR_DELETE, SQLITE_CANTOPEN). 
** The two subsequent arguments should be the name of the OS function that
** failed and the the associated file-system path, if any.
*/
//#define winLogError(a,b,c)     winLogErrorAtLine(a,b,c,__LINE__)
static int winLogError( int a, string b, string c )
{
  StackTrace st = new StackTrace( new StackFrame( true ) );
  StackFrame sf = st.GetFrame( 0 );
  
  return winLogErrorAtLine( a, b, c, sf.GetFileLineNumber() );
}

static int winLogErrorAtLine(
  int errcode,                    /* SQLite error code */
  string zFunc,                   /* Name of OS function that failed */
  string zPath,                   /* File path associated with error */
  int iLine                       /* Source line number where error occurred */
){
  string zMsg = null;             /* Human readable error text */
  int i;                          /* Loop counter */
  DWORD iErrno;// = GetLastError();  /* Error code */
#if SQLITE_SILVERLIGHT || SQLITE_WINRT
  iErrno = (int)ERROR_NOT_SUPPORTED;
#else
  iErrno = (u32)HelperMethods.GetLastError();
#endif

  //zMsg[0] = 0;
      getLastErrorMsg( 500, ref zMsg );
      Debug.Assert( errcode != SQLITE_OK );
  if ( zPath == null )
    zPath = "";
  for ( i = 0; i < zMsg.Length && zMsg[i] != '\r' && zMsg[i] != '\n'; i++ )
  {
  }
  zMsg = zMsg.Substring( 0, i );
  sqlite3_log(errcode,
      "os_win.c:%d: (%d) %s(%s) - %s",
      iLine, iErrno, zFunc, zPath, zMsg
  );

  return errcode;
}


#if SQLITE_OS_WINCE
/*************************************************************************
** This section contains code for WinCE only.
*/
/*
** WindowsCE does not have a localtime() function.  So create a
** substitute.
*/
//#include <time.h>
struct tm *__cdecl localtime(const time_t *t)
{
static struct tm y;
FILETIME uTm, lTm;
SYSTEMTIME pTm;
sqlite3_int64 t64;
t64 = *t;
t64 = (t64 + 11644473600)*10000000;
uTm.dwLowDateTime = (DWORD)(t64 & 0xFFFFFFFF);
uTm.dwHighDateTime= (DWORD)(t64 >> 32);
FileTimeToLocalFileTime(&uTm,&lTm);
FileTimeToSystemTime(&lTm,&pTm);
y.tm_year = pTm.wYear - 1900;
y.tm_mon = pTm.wMonth - 1;
y.tm_wday = pTm.wDayOfWeek;
y.tm_mday = pTm.wDay;
y.tm_hour = pTm.wHour;
y.tm_min = pTm.wMinute;
y.tm_sec = pTm.wSecond;
return &y;
}

/* This will never be called, but defined to make the code compile */
//#define GetTempPathA(a,b)

//#define LockFile(a,b,c,d,e)       winceLockFile(&a, b, c, d, e)
//#define UnlockFile(a,b,c,d,e)     winceUnlockFile(&a, b, c, d, e)
//#define LockFileEx(a,b,c,d,e,f)   winceLockFileEx(&a, b, c, d, e, f)

//#define HANDLE_TO_WINFILE(a) (winFile)&((char)a)[-(int)offsetof(winFile,h)]

/*
** Acquire a lock on the handle h
*/
static void winceMutexAcquire(HANDLE h){
DWORD dwErr;
do {
dwErr = WaitForSingleObject(h, INFINITE);
} while (dwErr != WAIT_OBJECT_0 && dwErr != WAIT_ABANDONED);
}
/*
** Release a lock acquired by winceMutexAcquire()
*/
//#define winceMutexRelease(h) ReleaseMutex(h)

/*
** Create the mutex and shared memory used for locking in the file
** descriptor pFile
*/
static BOOL winceCreateLock(string zFilename, sqlite3_file pFile){
Wstring zTok;
Wstring zName = utf8ToUnicode(zFilename);
BOOL bInit = TRUE;

/* Initialize the local lockdata */
ZeroMemory(pFile.local, pFile.local).Length;

/* Replace the backslashes from the filename and lowercase it
** to derive a mutex name. */
zTok = CharLowerW(zName);
for (;*zTok;zTok++){
if (*zTok == '\\') *zTok = '_';
}

/* Create/open the named mutex */
pFile.hMutex = CreateMutexW(NULL, FALSE, zName);
if (!pFile.hMutex){
pFile.lastErrno = (u32)GetLastError();
winLogError(SQLITE_ERROR, "winceCreateLock1", zFilename);
free(zName);
return FALSE;
}

/* Acquire the mutex before continuing */
winceMutexAcquire(pFile.hMutex);

/* Since the names of named mutexes, semaphores, file mappings etc are
** case-sensitive, take advantage of that by uppercasing the mutex name
** and using that as the shared filemapping name.
*/
CharUpperW(zName);
pFile.hShared = CreateFileMappingW(INVALID_HANDLE_VALUE, NULL,
PAGE_READWRITE, 0, winceLock.Length,
zName);

/* Set a flag that indicates we're the first to create the memory so it
** must be zero-initialized */
if (GetLastError() == ERROR_ALREADY_EXISTS){
bInit = FALSE;
}

free(zName);

/* If we succeeded in making the shared memory handle, map it. */
if (pFile.hShared){
pFile.shared = (winceLock)MapViewOfFile(pFile.hShared,
FILE_MAP_READ|FILE_MAP_WRITE, 0, 0, winceLock).Length;
/* If mapping failed, close the shared memory handle and erase it */
if (!pFile.shared){
pFile.lastErrno = (u32)GetLastError();
winLogError(SQLITE_ERROR, "winceCreateLock2", zFilename);
CloseHandle(pFile.hShared);
pFile.hShared = NULL;
}
}

/* If shared memory could not be created, then close the mutex and fail */
if (pFile.hShared == NULL){
winceMutexRelease(pFile.hMutex);
CloseHandle(pFile.hMutex);
pFile.hMutex = NULL;
return FALSE;
}

/* Initialize the shared memory if we're supposed to */
if (bInit) {
ZeroMemory(pFile.shared, winceLock).Length;
}

winceMutexRelease(pFile.hMutex);
return TRUE;
}

/*
** Destroy the part of sqlite3_file that deals with wince locks
*/
static void winceDestroyLock(sqlite3_file pFile){
if (pFile.hMutex){
/* Acquire the mutex */
winceMutexAcquire(pFile.hMutex);

/* The following blocks should probably Debug.Assert in debug mode, but they
are to cleanup in case any locks remained open */
if (pFile.local.nReaders){
pFile.shared.nReaders --;
}
if (pFile.local.bReserved){
pFile.shared.bReserved = FALSE;
}
if (pFile.local.bPending){
pFile.shared.bPending = FALSE;
}
if (pFile.local.bExclusive){
pFile.shared.bExclusive = FALSE;
}

/* De-reference and close our copy of the shared memory handle */
UnmapViewOfFile(pFile.shared);
CloseHandle(pFile.hShared);

/* Done with the mutex */
winceMutexRelease(pFile.hMutex);
CloseHandle(pFile.hMutex);
pFile.hMutex = NULL;
}
}

/*
** An implementation of the LockFile() API of windows for wince
*/
static BOOL winceLockFile(
HANDLE *phFile,
DWORD dwFileOffsetLow,
DWORD dwFileOffsetHigh,
DWORD nNumberOfBytesToLockLow,
DWORD nNumberOfBytesToLockHigh
){
winFile *pFile = HANDLE_TO_WINFILE(phFile);
BOOL bReturn = FALSE;

UNUSED_PARAMETER(dwFileOffsetHigh);
UNUSED_PARAMETER(nNumberOfBytesToLockHigh);

if (!pFile.hMutex) return TRUE;
winceMutexAcquire(pFile.hMutex);

/* Wanting an exclusive lock? */
if (dwFileOffsetLow == (DWORD)SHARED_FIRST
&& nNumberOfBytesToLockLow == (DWORD)SHARED_SIZE){
if (pFile.shared.nReaders == 0 && pFile.shared.bExclusive == 0){
pFile.shared.bExclusive = TRUE;
pFile.local.bExclusive = TRUE;
bReturn = TRUE;
}
}

/* Want a read-only lock? */
else if (dwFileOffsetLow == (DWORD)SHARED_FIRST &&
nNumberOfBytesToLockLow == 1){
if (pFile.shared.bExclusive == 0){
pFile.local.nReaders ++;
if (pFile.local.nReaders == 1){
pFile.shared.nReaders ++;
}
bReturn = TRUE;
}
}

/* Want a pending lock? */
else if (dwFileOffsetLow == (DWORD)PENDING_BYTE && nNumberOfBytesToLockLow == 1){
/* If no pending lock has been acquired, then acquire it */
if (pFile.shared.bPending == 0) {
pFile.shared.bPending = TRUE;
pFile.local.bPending = TRUE;
bReturn = TRUE;
}
}

/* Want a reserved lock? */
else if (dwFileOffsetLow == (DWORD)RESERVED_BYTE && nNumberOfBytesToLockLow == 1){
if (pFile.shared.bReserved == 0) {
pFile.shared.bReserved = TRUE;
pFile.local.bReserved = TRUE;
bReturn = TRUE;
}
}

winceMutexRelease(pFile.hMutex);
return bReturn;
}

/*
** An implementation of the UnlockFile API of windows for wince
*/
static BOOL winceUnlockFile(
HANDLE *phFile,
DWORD dwFileOffsetLow,
DWORD dwFileOffsetHigh,
DWORD nNumberOfBytesToUnlockLow,
DWORD nNumberOfBytesToUnlockHigh
){
winFile *pFile = HANDLE_TO_WINFILE(phFile);
BOOL bReturn = FALSE;

UNUSED_PARAMETER(dwFileOffsetHigh);
UNUSED_PARAMETER(nNumberOfBytesToUnlockHigh);

if (!pFile.hMutex) return TRUE;
winceMutexAcquire(pFile.hMutex);

/* Releasing a reader lock or an exclusive lock */
if (dwFileOffsetLow == (DWORD)SHARED_FIRST){
/* Did we have an exclusive lock? */
if (pFile.local.bExclusive){
Debug.Assert(nNumberOfBytesToUnlockLow == (DWORD)SHARED_SIZE);
pFile.local.bExclusive = FALSE;
pFile.shared.bExclusive = FALSE;
bReturn = TRUE;
}

/* Did we just have a reader lock? */
else if (pFile.local.nReaders){
Debug.Assert(nNumberOfBytesToUnlockLow == (DWORD)SHARED_SIZE || nNumberOfBytesToUnlockLow == 1);
pFile.local.nReaders --;
if (pFile.local.nReaders == 0)
{
pFile.shared.nReaders --;
}
bReturn = TRUE;
}
}

/* Releasing a pending lock */
else if (dwFileOffsetLow == (DWORD)PENDING_BYTE && nNumberOfBytesToUnlockLow == 1){
if (pFile.local.bPending){
pFile.local.bPending = FALSE;
pFile.shared.bPending = FALSE;
bReturn = TRUE;
}
}
/* Releasing a reserved lock */
else if (dwFileOffsetLow == (DWORD)RESERVED_BYTE && nNumberOfBytesToUnlockLow == 1){
if (pFile.local.bReserved) {
pFile.local.bReserved = FALSE;
pFile.shared.bReserved = FALSE;
bReturn = TRUE;
}
}

winceMutexRelease(pFile.hMutex);
return bReturn;
}

/*
** An implementation of the LockFileEx() API of windows for wince
*/
static BOOL winceLockFileEx(
HANDLE *phFile,
DWORD dwFlags,
DWORD dwReserved,
DWORD nNumberOfBytesToLockLow,
DWORD nNumberOfBytesToLockHigh,
LPOVERLAPPED lpOverlapped
){
UNUSED_PARAMETER(dwReserved);
UNUSED_PARAMETER(nNumberOfBytesToLockHigh);

/* If the caller wants a shared read lock, forward this call
** to winceLockFile */
if (lpOverlapped.Offset == (DWORD)SHARED_FIRST &&
dwFlags == 1 &&
nNumberOfBytesToLockLow == (DWORD)SHARED_SIZE){
return winceLockFile(phFile, SHARED_FIRST, 0, 1, 0);
}
return FALSE;
}
/*
** End of the special code for wince
*****************************************************************************/
#endif // * SQLITE_OS_WINCE */

    /*****************************************************************************
** The next group of routines implement the I/O methods specified
** by the sqlite3_io_methods object.
******************************************************************************/

    /*
    ** Some microsoft compilers lack this definition.
    */
#if !INVALID_SET_FILE_POINTER
    //# define INVALID_SET_FILE_POINTER ((DWORD)-1)
    const int INVALID_SET_FILE_POINTER = -1;
#endif

    /*
** Move the current position of the file handle passed as the first 
** argument to offset iOffset within the file. If successful, return 0. 
** Otherwise, set pFile->lastErrno and return non-zero.
*/
    static int seekWinFile( sqlite3_file id, sqlite3_int64 iOffset )
    {
      //LONG upperBits;                 /* Most sig. 32 bits of new offset */
      //LONG lowerBits;                 /* Least sig. 32 bits of new offset */
      DWORD dwRet;                    /* Value returned by SetFilePointer() */
      sqlite3_file pFile = id;

      //upperBits = (LONG)((iOffset>>32) & 0x7fffffff);
      //lowerBits = (LONG)(iOffset & 0xffffffff);

      /* API oddity: If successful, SetFilePointer() returns a dword 
      ** containing the lower 32-bits of the new file-offset. Or, if it fails,
      ** it returns INVALID_SET_FILE_POINTER. However according to MSDN, 
      ** INVALID_SET_FILE_POINTER may also be a valid new offset. So to determine 
      ** whether an error has actually occured, it is also necessary to call 
      ** GetLastError().
      */
      //dwRet = SetFilePointer(id, lowerBits, &upperBits, FILE_BEGIN);
      //if( (dwRet==INVALID_SET_FILE_POINTER && GetLastError()!=NO_ERROR) ){
      //  pFile->lastErrno = GetLastError();
      //  winLogError(SQLITE_IOERR_SEEK, "seekWinFile", pFile->zPath);
      try
      {
#if SQLITE_WINRT
        id.fs.Seek( (ulong)iOffset ); // SetFilePointer(pFile.fs.Name, lowerBits, upperBits, FILE_BEGIN);
#else
        id.fs.Seek( iOffset, SeekOrigin.Begin ); // SetFilePointer(pFile.fs.Name, lowerBits, upperBits, FILE_BEGIN);
#endif
      }
      catch ( Exception e )
      {
#if SQLITE_SILVERLIGHT || SQLITE_WINRT
          pFile.lastErrno = 1;
#else
        pFile.lastErrno = (u32)HelperMethods.GetLastError();
#endif
        winLogError(SQLITE_IOERR_SEEK, "seekWinFile", pFile.zPath);
        return 1;
      }

      return 0;
    }

    /*
    ** Close a file.
    **
    ** It is reported that an attempt to close a handle might sometimes
    ** fail.  This is a very unreasonable result, but windows is notorious
    ** for being unreasonable so I do not doubt that it might happen.  If
    ** the close fails, we pause for 100 milliseconds and try again.  As
    ** many as MX_CLOSE_ATTEMPT attempts to close the handle are made before
    ** giving up and returning an error.
    */
    public static int MX_CLOSE_ATTEMPT = 3;
    static int winClose( sqlite3_file id )
    {
      bool rc;
      int cnt = 0;
      sqlite3_file pFile = (sqlite3_file)id;

      Debug.Assert( id != null );
      Debug.Assert( pFile.pShm == null );
#if SQLITE_DEBUG
      OSTRACE( "CLOSE %d (%s)\n", pFile.fs.GetHashCode(), pFile.fs.Name );
#endif
      do
      {
#if SQLITE_WINRT
        pFile.fs.Dispose();
#else
        pFile.fs.Close();
#endif
        rc = true;
        //  rc = CloseHandle(pFile.h);
        /* SimulateIOError( rc=0; cnt=MX_CLOSE_ATTEMPT; ); */
        //  if (!rc && ++cnt < MX_CLOSE_ATTEMPT) Thread.Sleep(100); //, 1) );
      } while ( !rc && ++cnt < MX_CLOSE_ATTEMPT ); //, 1) );
#if SQLITE_OS_WINCE
//#define WINCE_DELETION_ATTEMPTS 3
winceDestroyLock(pFile);
if( pFile.zDeleteOnClose ){
int cnt = 0;
while(
DeleteFileW(pFile.zDeleteOnClose)==0
&& GetFileAttributesW(pFile.zDeleteOnClose)!=0xffffffff
&& cnt++ < WINCE_DELETION_ATTEMPTS
){
Sleep(100);  /* Wait a little before trying again */
}
free(pFile.zDeleteOnClose);
}
#endif
#if SQLITE_TEST
      OSTRACE( "CLOSE %d %s\n", pFile.fs.GetHashCode(), rc ? "ok" : "failed" );
      OpenCounter( -1 );
#endif
      return rc ? SQLITE_OK : winLogError(SQLITE_IOERR_CLOSE, "winClose", pFile.zPath);
    }


    /*
    ** Read data from a file into a buffer.  Return SQLITE_OK if all
    ** bytes were read successfully and SQLITE_IOERR if anything goes
    ** wrong.
    */
    static int winRead(
    sqlite3_file id,           /* File to read from */
    byte[] pBuf,               /* Write content into this buffer */
    int amt,                   /* Number of bytes to read */
    sqlite3_int64 offset       /* Begin reading at this offset */
    )
    {

      long rc;
      sqlite3_file pFile = id;
      int nRead;                    /* Number of bytes actually read from file */

      Debug.Assert( id != null );
#if SQLITE_TEST
      if ( SimulateIOError() )
        return SQLITE_IOERR_READ;
#endif
#if SQLITE_DEBUG
      OSTRACE( "READ %d lock=%d\n", pFile.fs.GetHashCode(), pFile.locktype );
#endif
      if ( !id.fs.CanRead )
        return SQLITE_IOERR_READ;
      if ( seekWinFile( pFile, offset ) != 0 )
      {
        return SQLITE_FULL;
      }

      try
      {
#if SQLITE_WINRT
          using (IInputStream inputStream = id.fs.GetInputStreamAt((ulong)offset))
          {
              IBuffer buffer = pBuf.AsBuffer(0,0,pBuf.Length);
              inputStream.ReadAsync(buffer, (uint)amt, InputStreamOptions.None).AsTask().Wait();
              nRead = (int)buffer.Length;
          }
#else
        nRead = id.fs.Read( pBuf, 0, amt ); // i  if( null==ReadFile(pFile->h, pBuf, amt, &nRead, 0) ){
#endif
      }
      catch ( Exception e )
      {
#if SQLITE_SILVERLIGHT || SQLITE_WINRT
          pFile.lastErrno = 1;
#else
        pFile.lastErrno = (u32)HelperMethods.GetLastError();
#endif
        return winLogError(SQLITE_IOERR_READ, "winRead", pFile.zPath);
      }
      if ( nRead < amt )
      {
        /* Unread parts of the buffer must be zero-filled */
        Array.Clear( pBuf, (int)nRead, (int)( amt - nRead ) ); // memset(&((char)pBuf)[nRead], 0, amt-nRead);
        return SQLITE_IOERR_SHORT_READ;
      }
      return SQLITE_OK;
    }

    /*
    ** Write data from a buffer into a file.  Return SQLITE_OK on success
    ** or some other error code on failure.
    */
    static int winWrite(
    sqlite3_file id,          /* File to write into */
    byte[] pBuf,              /* The bytes to be written */
    int amt,                  /* Number of bytes to write */
    sqlite3_int64 offset      /* Offset into the file to begin writing at */
    )
    {
      int rc;                         /* True if error has occured, else false */
      sqlite3_file pFile = id;        /* File handle */

      Debug.Assert( amt > 0 );
      Debug.Assert( pFile != null );

#if SQLITE_TEST
      if ( SimulateIOError() )
        return SQLITE_IOERR_WRITE;
      if ( SimulateDiskfullError() )
        return SQLITE_FULL;
#endif
#if SQLITE_DEBUG
      OSTRACE( "WRITE %d lock=%d\n", id.fs.GetHashCode(), id.locktype );
#endif
      rc = seekWinFile( pFile, offset );
      //if( rc==0 ){
      //  u8 *aRem = (u8 )pBuf;        /* Data yet to be written */
      //  int nRem = amt;               /* Number of bytes yet to be written */
      //  DWORD nWrite;                 /* Bytes written by each WriteFile() call */

      //  while( nRem>0 && WriteFile(pFile->h, aRem, nRem, &nWrite, 0) && nWrite>0 ){
      //    aRem += nWrite;
      //    nRem -= nWrite;
      //  }
#if SQLITE_WINRT
     ulong wrote = id.fs.Position;
#else
      long wrote = id.fs.Position;
#endif
      try
      {
        Debug.Assert( pBuf.Length >= amt );
#if SQLITE_WINRT
        using (IOutputStream outStream = id.fs.GetOutputStreamAt((ulong)offset))
        {
            outStream.WriteAsync(pBuf.AsBuffer(0, amt)).AsTask().Wait();
            outStream.FlushAsync().AsTask().Wait();
            wrote = (ulong)amt;
        }
#else
        id.fs.Write( pBuf, 0, amt );
        wrote = id.fs.Position - wrote;
#endif
        rc = 1;// Success
      }
      catch ( IOException e )
      {
        return SQLITE_READONLY;
      }

      if ( rc == 0 || amt > (int)wrote )
      {
#if SQLITE_SILVERLIGHT || SQLITE_WINRT
          id.lastErrno  = 1;
#else
        id.lastErrno = (u32)HelperMethods.GetLastError();
#endif
        if (( id.lastErrno == ERROR_HANDLE_DISK_FULL )
        || ( id.lastErrno == ERROR_DISK_FULL ))
        {
          return SQLITE_FULL;
        }
        else
        {
          return winLogError(SQLITE_IOERR_WRITE, "winWrite", pFile.zPath);
        }
      }
      return SQLITE_OK;
    }

    /*
    ** Truncate an open file to a specified size
    */
    static int winTruncate( sqlite3_file id, sqlite3_int64 nByte )
    {
      sqlite3_file pFile = id;        /* File handle object */
      int rc = SQLITE_OK;             /* Return code for this function */

      Debug.Assert( pFile != null );
#if SQLITE_DEBUG
#if WINDOWS_PHONE || SQLITE_SILVERLIGHT
      OSTRACE( "TRUNCATE %d %lld\n", id.fs.GetHashCode(), nByte );
#else
      OSTRACE( "TRUNCATE %s %lld\n", id.fs.Name, nByte );
#endif
#endif
#if SQLITE_TEST
      if ( SimulateIOError() )
        return SQLITE_IOERR_TRUNCATE;
      if ( SimulateIOError() )
        return SQLITE_IOERR_TRUNCATE;
#endif

      /* If the user has configured a chunk-size for this file, truncate the
** file so that it consists of an integer number of chunks (i.e. the
** actual file size after the operation may be larger than the requested
** size).
*/

      if ( pFile.szChunk != 0 )
      {
        nByte = ( ( nByte + pFile.szChunk - 1 ) / pFile.szChunk ) * pFile.szChunk;
      }

      /* SetEndOfFile() returns non-zero when successful, or zero when it fails. */
      //if ( seekWinFile( pFile, nByte ) )
      //{
      //  rc = winLogError(SQLITE_IOERR_TRUNCATE, "winTruncate1", pFile->zPath);
      //}
      //else if( 0==SetEndOfFile(pFile->h) ){
      //  pFile->lastErrno = GetLastError();
      //  rc = winLogError(SQLITE_IOERR_TRUNCATE, "winTruncate2", pFile->zPath);
      //}
      try
      {
#if SQLITE_WINRT
        id.fs.Size = (ulong)nByte;
#else
        id.fs.SetLength( nByte );
#endif
        rc = SQLITE_OK;
      }
      catch ( IOException e )
      {
#if SQLITE_SILVERLIGHT || SQLITE_WINRT
          id.lastErrno  = 1;
#else
        id.lastErrno = (u32)HelperMethods.GetLastError();
#endif
        rc = winLogError(SQLITE_IOERR_TRUNCATE, "winTruncate2", pFile.zPath);
      }
      OSTRACE( "TRUNCATE %d %lld %s\n", id.fs.GetHashCode(), nByte, rc == SQLITE_OK ? "ok" : "failed" );
      return rc;
    }

#if SQLITE_TEST
    /*
** Count the number of fullsyncs and normal syncs.  This is used to test
** that syncs and fullsyncs are occuring at the right times.
*/
#if !TCLSH
    static int sqlite3_sync_count = 0;
    static int sqlite3_fullsync_count = 0;
#else
    static tcl.lang.Var.SQLITE3_GETSET sqlite3_sync_count = new tcl.lang.Var.SQLITE3_GETSET( "sqlite3_sync_count" );
    static tcl.lang.Var.SQLITE3_GETSET sqlite3_fullsync_count = new tcl.lang.Var.SQLITE3_GETSET( "sqlite_fullsync_count" );
#endif
#endif

    /*
** Make sure all writes to a particular file are committed to disk.
*/
    static int winSync( sqlite3_file id, int flags )
    {
#if !(NDEBUG) || !(SQLITE_NO_SYNC) || (SQLITE_DEBUG)
      sqlite3_file pFile = (sqlite3_file)id;
      bool rc;
#else
UNUSED_PARAMETER(id);
#endif
      Debug.Assert( pFile != null );
      /* Check that one of SQLITE_SYNC_NORMAL or FULL was passed */
      Debug.Assert( ( flags & 0x0F ) == SQLITE_SYNC_NORMAL
      || ( flags & 0x0F ) == SQLITE_SYNC_FULL
      );

      OSTRACE( "SYNC %d lock=%d\n", pFile.fs.GetHashCode(), pFile.locktype );

  /* Unix cannot, but some systems may return SQLITE_FULL from here. This
  ** line is to test that doing so does not cause any problems.
  */
#if SQLITE_TEST
        if ( SimulateDiskfullError() )
        return SQLITE_FULL;
#endif
#if !SQLITE_TEST
UNUSED_PARAMETER(flags);
#else
      if ( (flags&0x0F)==SQLITE_SYNC_FULL )
      {
#if !TCLSH
        sqlite3_fullsync_count++;
      }
      sqlite3_sync_count++;
#else
        sqlite3_fullsync_count.iValue++;
      }
      sqlite3_sync_count.iValue++;
#endif
#endif


      /* If we compiled with the SQLITE_NO_SYNC flag, then syncing is a
** no-op
*/
#if SQLITE_NO_SYNC
return SQLITE_OK;
#else
#if SQLITE_WINRT
    Stream stream = pFile.fs.AsStreamForWrite();
    stream.Flush();
#else
      pFile.fs.Flush();
#endif
      return SQLITE_OK;
  //rc = FlushFileBuffers(pFile->h);
  //SimulateIOError( rc=FALSE );
  //if( rc ){
  //  return SQLITE_OK;
  //}else{
  //  pFile->lastErrno = GetLastError();
  //  return winLogError(SQLITE_IOERR_FSYNC, "winSync", pFile->zPath);
  //}

#endif
    }

    /*
    ** Determine the current size of a file in bytes
    */
    static int winFileSize( sqlite3_file id, ref long pSize )
    {
      //DWORD upperBits;
      //DWORD lowerBits;
      //  sqlite3_file pFile = (sqlite3_file)id;
      //  DWORD error;
      Debug.Assert( id != null );
#if SQLITE_TEST
      if ( SimulateIOError() )
        return SQLITE_IOERR_FSTAT;
#endif
      //lowerBits = GetFileSize(pFile.fs.Name, upperBits);
      //if ( ( lowerBits == INVALID_FILE_SIZE )
      //   && ( ( error = GetLastError() ) != NO_ERROR ) )
      //{
      //  pFile.lastErrno = error;
      //  return winLogError(SQLITE_IOERR_FSTAT, "winFileSize", pFile->zPath);
      //}
      //pSize = (((sqlite3_int64)upperBits)<<32) + lowerBits;
#if SQLITE_WINRT
     pSize = id.fs.CanRead ? (long)id.fs.Size : 0;
#else
      pSize = id.fs.CanRead ? id.fs.Length : 0;
#endif
      return SQLITE_OK;
    }


    /*
    ** Acquire a reader lock.
    ** Different API routines are called depending on whether or not this
    ** is Win95 or WinNT.
    */
    static int getReadLock( sqlite3_file pFile )
    {
      int res = 0;
      if ( isNT() )
      {
        res = lockingStrategy.SharedLockFile( pFile, SHARED_FIRST, SHARED_SIZE );
      }
      /* isNT() is 1 if SQLITE_OS_WINCE==1, so this else is never executed.
      */
#if !SQLITE_OS_WINCE
      //else
      //{
      //  int lk;
      //  sqlite3_randomness(lk.Length, lk);
      //  pFile.sharedLockByte = (u16)((lk & 0x7fffffff)%(SHARED_SIZE - 1));
      //  res = pFile.fs.Lock( SHARED_FIRST + pFile.sharedLockByte, 0, 1, 0);
#endif
      //}
        if (res == 0) {
            pFile.lastErrno = (u32)HelperMethods.GetLastError();
        }
        /* No need to log a failure to lock */
      return res;
    }

    /*
    ** Undo a readlock
    */
    static int unlockReadLock( sqlite3_file pFile )
    {
      int res = 1;
      if ( isNT() )
      {
        try
        {
          lockingStrategy.UnlockFile( pFile, SHARED_FIRST, SHARED_SIZE ); //     res = UnlockFile(pFile.h, SHARED_FIRST, 0, SHARED_SIZE, 0);
        }
        catch ( Exception e )
        {
          res = 0;
        }
      }
      /* isNT() is 1 if SQLITE_OS_WINCE==1, so this else is never executed.
      */
#if !SQLITE_OS_WINCE
      else
      {
        Debugger.Break(); //    res = UnlockFile(pFile.h, SHARED_FIRST + pFilE.sharedLockByte, 0, 1, 0);
      }
#endif
        if (res == 0) {
            pFile.lastErrno = (u32)HelperMethods.GetLastError();

            winLogError(SQLITE_IOERR_UNLOCK, "unlockReadLock", pFile.zPath);
        }

        return res;
    }

    /*
    ** Lock the file with the lock specified by parameter locktype - one
    ** of the following:
    **
    **     (1) SHARED_LOCK
    **     (2) RESERVED_LOCK
    **     (3) PENDING_LOCK
    **     (4) EXCLUSIVE_LOCK
    **
    ** Sometimes when requesting one lock state, additional lock states
    ** are inserted in between.  The locking might fail on one of the later
    ** transitions leaving the lock state different from what it started but
    ** still short of its goal.  The following chart shows the allowed
    ** transitions and the inserted intermediate states:
    **
    **    UNLOCKED . SHARED
    **    SHARED . RESERVED
    **    SHARED . (PENDING) . EXCLUSIVE
    **    RESERVED . (PENDING) . EXCLUSIVE
    **    PENDING . EXCLUSIVE
    **
    ** This routine will only increase a lock.  The winUnlock() routine
    ** erases all locks at once and returns us immediately to locking level 0.
    ** It is not possible to lower the locking level one step at a time.  You
    ** must go straight to locking level 0.
    */
    static int winLock( sqlite3_file id, int locktype )
    {
      int rc = SQLITE_OK;         /* Return code from subroutines */
      int res = 1;                /* Result of a windows lock call */
      int newLocktype;            /* Set pFile.locktype to this value before exiting */
      bool gotPendingLock = false;/* True if we acquired a PENDING lock this time */
      sqlite3_file pFile = (sqlite3_file)id;
      DWORD error = NO_ERROR;

      Debug.Assert( id != null );
#if SQLITE_DEBUG
      OSTRACE( "LOCK %d %d was %d(%d)\n",
      pFile.fs.GetHashCode(), locktype, pFile.locktype, pFile.sharedLockByte );
#endif
      /* If there is already a lock of this type or more restrictive on the
** OsFile, do nothing. Don't use the end_lock: exit path, as
** sqlite3OsEnterMutex() hasn't been called yet.
*/
      if ( pFile.locktype >= locktype )
      {
        return SQLITE_OK;
      }

      /* Make sure the locking sequence is correct
      */
      Debug.Assert( pFile.locktype != NO_LOCK || locktype == SHARED_LOCK );
      Debug.Assert( locktype != PENDING_LOCK );
      Debug.Assert( locktype != RESERVED_LOCK || pFile.locktype == SHARED_LOCK );

      /* Lock the PENDING_LOCK byte if we need to acquire a PENDING lock or
      ** a SHARED lock.  If we are acquiring a SHARED lock, the acquisition of
      ** the PENDING_LOCK byte is temporary.
      */
      newLocktype = pFile.locktype;
      if ( pFile.locktype == NO_LOCK
      || ( ( locktype == EXCLUSIVE_LOCK )
      && ( pFile.locktype == RESERVED_LOCK ) )
      )
      {
        int cnt = 3;
        res = 0;
        while ( cnt-- > 0 && res == 0 )//(res = LockFile(pFile.fs.SafeFileHandle.DangerousGetHandle().ToInt32(), PENDING_BYTE, 0, 1, 0)) == 0)
        {
          try
          {
            lockingStrategy.LockFile( pFile, PENDING_BYTE, 1 );
            res = 1;
          }
          catch ( Exception e )
          {
            /* Try 3 times to get the pending lock.  The pending lock might be
            ** held by another reader process who will release it momentarily.
            */
#if SQLITE_DEBUG
            OSTRACE( "could not get a PENDING lock. cnt=%d\n", cnt );
#endif
#if SQLITE_WINRT
              System.Threading.Tasks.Task.Delay(1).Wait();

#else
            Thread.Sleep( 1 );
#endif
          }
        }
        gotPendingLock = ( res != 0 );
        if ( 0 == res )
        {
#if SQLITE_SILVERLIGHT || SQLITE_WINRT
            error = 1;
#else
          error = (u32)HelperMethods.GetLastError();
#endif
        }
      }

      /* Acquire a shared lock
      */
      if ( locktype == SHARED_LOCK && res != 0 )
      {
        Debug.Assert( pFile.locktype == NO_LOCK );
        res = getReadLock( pFile );
        if ( res != 0 )
        {
          newLocktype = SHARED_LOCK;
        }
        else
        {
#if SQLITE_SILVERLIGHT || SQLITE_WINRT
            error = 1;
#else
          error = (u32)HelperMethods.GetLastError();
#endif
        }
      }

      /* Acquire a RESERVED lock
      */
      if ( ( locktype == RESERVED_LOCK ) && res != 0 )
      {
        Debug.Assert( pFile.locktype == SHARED_LOCK );
        try
        {
          lockingStrategy.LockFile( pFile, RESERVED_BYTE, 1 );//res = LockFile(pFile.fs.SafeFileHandle.DangerousGetHandle().ToInt32(), RESERVED_BYTE, 0, 1, 0);
          newLocktype = RESERVED_LOCK;
          res = 1;
        }
        catch ( Exception e )
        {
          res = 0;
#if SQLITE_SILVERLIGHT || SQLITE_WINRT
          error = 1;
#else
          error = (u32)HelperMethods.GetLastError();
#endif
        }
        if ( res != 0 )
        {
          newLocktype = RESERVED_LOCK;
        }
        else
        {
#if SQLITE_SILVERLIGHT
error = 1;
#else
          error = (u32)HelperMethods.GetLastError();
#endif
        }
      }

      /* Acquire a PENDING lock
      */
      if ( locktype == EXCLUSIVE_LOCK && res != 0 )
      {
        newLocktype = PENDING_LOCK;
        gotPendingLock = false;
      }

      /* Acquire an EXCLUSIVE lock
      */
      if ( locktype == EXCLUSIVE_LOCK && res != 0 )
      {
        Debug.Assert( pFile.locktype >= SHARED_LOCK );
        res = unlockReadLock( pFile );
#if SQLITE_DEBUG
        OSTRACE( "unreadlock = %d\n", res );
#endif
        //res = LockFile(pFile.fs.SafeFileHandle.DangerousGetHandle().ToInt32(), SHARED_FIRST, 0, SHARED_SIZE, 0);
        try
        {
          lockingStrategy.LockFile( pFile, SHARED_FIRST, SHARED_SIZE );
          newLocktype = EXCLUSIVE_LOCK;
          res = 1;
        }
        catch ( Exception e )
        {
          res = 0;
        }
        if ( res != 0 )
        {
          newLocktype = EXCLUSIVE_LOCK;
        }
        else
        {
#if SQLITE_SILVERLIGHT || SQLITE_WINRT
            error = 1;
#else
          error = (u32)HelperMethods.GetLastError();
#endif
#if SQLITE_DEBUG
          OSTRACE( "error-code = %d\n", error );
#endif
          getReadLock( pFile );
        }
      }

      /* If we are holding a PENDING lock that ought to be released, then
      ** release it now.
      */
      if ( gotPendingLock && locktype == SHARED_LOCK )
      {
        lockingStrategy.UnlockFile( pFile, PENDING_BYTE, 1 );
      }

      /* Update the state of the lock has held in the file descriptor then
      ** return the appropriate result code.
      */
      if ( res != 0 )
      {
        rc = SQLITE_OK;
      }
      else
      {
#if SQLITE_DEBUG
        OSTRACE( "LOCK FAILED %d trying for %d but got %d\n", pFile.fs.GetHashCode(),
        locktype, newLocktype );
#endif
        pFile.lastErrno = error;
        rc = SQLITE_BUSY;
      }
      pFile.locktype = (u8)newLocktype;
      return rc;
    }

    /*
    ** This routine checks if there is a RESERVED lock held on the specified
    ** file by this or any other process. If such a lock is held, return
    ** non-zero, otherwise zero.
    */
    static int winCheckReservedLock( sqlite3_file id, ref int pResOut )
    {
      int rc;
      sqlite3_file pFile = (sqlite3_file)id;

      if ( SimulateIOError() )
        return SQLITE_IOERR_CHECKRESERVEDLOCK;

      Debug.Assert( id != null );
      if ( pFile.locktype >= RESERVED_LOCK )
      {
        rc = 1;
#if SQLITE_DEBUG
        OSTRACE( "TEST WR-LOCK %s %d (local)\n", pFile.fs.Name, rc );
#endif
      }
      else
      {
        try
        {
          lockingStrategy.LockFile( pFile, RESERVED_BYTE, 1 );
          lockingStrategy.UnlockFile( pFile, RESERVED_BYTE, 1 );
          rc = 1;
        }
        catch ( IOException e )
        {
          rc = 0;
        }
        rc = 1 - rc; // !rc
#if SQLITE_DEBUG
        OSTRACE( "TEST WR-LOCK %d %d (remote)\n", pFile.fs.GetHashCode(), rc );
#endif
      }
      pResOut = rc;
      return SQLITE_OK;
    }

    /*
    ** Lower the locking level on file descriptor id to locktype.  locktype
    ** must be either NO_LOCK or SHARED_LOCK.
    **
    ** If the locking level of the file descriptor is already at or below
    ** the requested locking level, this routine is a no-op.
    **
    ** It is not possible for this routine to fail if the second argument
    ** is NO_LOCK.  If the second argument is SHARED_LOCK then this routine
    ** might return SQLITE_IOERR;
    */
    static int winUnlock( sqlite3_file id, int locktype )
    {
      int type;
      sqlite3_file pFile = (sqlite3_file)id;
      int rc = SQLITE_OK;
      Debug.Assert( pFile != null );
      Debug.Assert( locktype <= SHARED_LOCK );

#if SQLITE_DEBUG
      OSTRACE( "UNLOCK %d to %d was %d(%d)\n", pFile.fs.GetHashCode(), locktype,
      pFile.locktype, pFile.sharedLockByte );
#endif
      type = pFile.locktype;
      if ( type >= EXCLUSIVE_LOCK )
      {
        lockingStrategy.UnlockFile( pFile, SHARED_FIRST, SHARED_SIZE ); // UnlockFile(pFile.h, SHARED_FIRST, 0, SHARED_SIZE, 0);
        if ( locktype == SHARED_LOCK && getReadLock( pFile ) == 0 )
        {
          /* This should never happen.  We should always be able to
          ** reacquire the read lock */
          rc = winLogError(SQLITE_IOERR_UNLOCK, "winUnlock", pFile.zPath);
        }
      }
      if ( type >= RESERVED_LOCK )
      {
        try
        {
          lockingStrategy.UnlockFile( pFile, RESERVED_BYTE, 1 );// UnlockFile(pFile.h, RESERVED_BYTE, 0, 1, 0);
        }
        catch ( Exception e )
        {
        }
      }
      if ( locktype == NO_LOCK && type >= SHARED_LOCK )
      {
        unlockReadLock( pFile );
      }
      if ( type >= PENDING_LOCK )
      {
        try
        {
          lockingStrategy.UnlockFile( pFile, PENDING_BYTE, 1 );//    UnlockFile(pFile.h, PENDING_BYTE, 0, 1, 0);
        }
        catch ( Exception e )
        {
        }
      }
      pFile.locktype = (u8)locktype;
      return rc;
    }

    /*
    ** Control and query of the open file handle.
    */
    static int winFileControl( sqlite3_file id, int op, ref sqlite3_int64 pArg )
    {
      switch ( op )
      {
        case SQLITE_FCNTL_LOCKSTATE:
          {
            pArg = (int)( (sqlite3_file)id ).locktype;
            return SQLITE_OK;
          }
        case SQLITE_LAST_ERRNO:
          {
            pArg = (int)( (sqlite3_file)id ).lastErrno;
            return SQLITE_OK;
          }
        case SQLITE_FCNTL_CHUNK_SIZE:
          {
            ( (sqlite3_file)id ).szChunk = (int)pArg;
            return SQLITE_OK;
          }
        case SQLITE_FCNTL_SIZE_HINT:
          {
            sqlite3_int64 sz = (sqlite3_int64)pArg;
            SimulateIOErrorBenign( 1 );
            winTruncate( id, sz );
            SimulateIOErrorBenign( 0 );
            return SQLITE_OK;
          }
        case SQLITE_FCNTL_SYNC_OMITTED:
          {
            return SQLITE_OK;
          }
      }
      return SQLITE_NOTFOUND;
    }

    /*
    ** Return the sector size in bytes of the underlying block device for
    ** the specified file. This is almost always 512 bytes, but may be
    ** larger for some devices.
    **
    ** SQLite code assumes this function cannot fail. It also assumes that
    ** if two files are created in the same file-system directory (i.e.
    ** a database and its journal file) that the sector size will be the
    ** same for both.
    */
    static int winSectorSize( sqlite3_file id )
    {
      Debug.Assert( id != null );
      return (int)( id.sectorSize );
    }

    /*
    ** Return a vector of device characteristics.
    */
    static int winDeviceCharacteristics( sqlite3_file id )
    {
      UNUSED_PARAMETER( id );
      return 0;
    }

#if !SQLITE_OMIT_WAL


/* 
** Windows will only let you create file view mappings
** on allocation size granularity boundaries.
** During sqlite3_os_init() we do a GetSystemInfo()
** to get the granularity size.
*/
SYSTEM_INFO winSysInfo;

/*
** Helper functions to obtain and relinquish the global mutex. The
** global mutex is used to protect the winLockInfo objects used by 
** this file, all of which may be shared by multiple threads.
**
** Function winShmMutexHeld() is used to Debug.Assert() that the global mutex 
** is held when required. This function is only used as part of Debug.Assert() 
** statements. e.g.
**
**   winShmEnterMutex()
**     Debug.Assert( winShmMutexHeld() );
**   winShmLeaveMutex()
*/
static void winShmEnterMutex(void){
  sqlite3_mutex_enter(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER));
}
static void winShmLeaveMutex(void){
  sqlite3_mutex_leave(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER));
}
#if SQLITE_DEBUG
static int winShmMutexHeld(void) {
  return sqlite3_mutex_held(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER));
}
#endif

/*
** Object used to represent a single file opened and mmapped to provide
** shared memory.  When multiple threads all reference the same
** log-summary, each thread has its own winFile object, but they all
** point to a single instance of this object.  In other words, each
** log-summary is opened only once per process.
**
** winShmMutexHeld() must be true when creating or destroying
** this object or while reading or writing the following fields:
**
**      nRef
**      pNext 
**
** The following fields are read-only after the object is created:
** 
**      fid
**      zFilename
**
** Either winShmNode.mutex must be held or winShmNode.nRef==0 and
** winShmMutexHeld() is true when reading or writing any other field
** in this structure.
**
*/
struct winShmNode {
  sqlite3_mutex *mutex;      /* Mutex to access this object */
  string zFilename;           /* Name of the file */
  winFile hFile;             /* File handle from winOpen */

  int szRegion;              /* Size of shared-memory regions */
  int nRegion;               /* Size of array apRegion */
  struct ShmRegion {
    HANDLE hMap;             /* File handle from CreateFileMapping */
    void *pMap;
  } *aRegion;
  DWORD lastErrno;           /* The Windows errno from the last I/O error */

  int nRef;                  /* Number of winShm objects pointing to this */
  winShm *pFirst;            /* All winShm objects pointing to this */
  winShmNode *pNext;         /* Next in list of all winShmNode objects */
#if SQLITE_DEBUG
  u8 nextShmId;              /* Next available winShm.id value */
#endif
};

/*
** A global array of all winShmNode objects.
**
** The winShmMutexHeld() must be true while reading or writing this list.
*/
static winShmNode *winShmNodeList = 0;

/*
** Structure used internally by this VFS to record the state of an
** open shared memory connection.
**
** The following fields are initialized when this object is created and
** are read-only thereafter:
**
**    winShm.pShmNode
**    winShm.id
**
** All other fields are read/write.  The winShm.pShmNode->mutex must be held
** while accessing any read/write fields.
*/
struct winShm {
  winShmNode *pShmNode;      /* The underlying winShmNode object */
  winShm *pNext;             /* Next winShm with the same winShmNode */
  u8 hasMutex;               /* True if holding the winShmNode mutex */
  u16 sharedMask;            /* Mask of shared locks held */
  u16 exclMask;              /* Mask of exclusive locks held */
#if SQLITE_DEBUG
  u8 id;                     /* Id of this connection with its winShmNode */
#endif
};

/*
** Constants used for locking
*/
//#define WIN_SHM_BASE   ((22+SQLITE_SHM_NLOCK)*4)        /* first lock byte */
//#define WIN_SHM_DMS    (WIN_SHM_BASE+SQLITE_SHM_NLOCK)  /* deadman switch */

/*
** Apply advisory locks for all n bytes beginning at ofst.
*/
//#define _SHM_UNLCK  1
//#define _SHM_RDLCK  2
//#define _SHM_WRLCK  3
static int winShmSystemLock(
  winShmNode *pFile,    /* Apply locks to this open shared-memory segment */
  int lockType,         /* _SHM_UNLCK, _SHM_RDLCK, or _SHM_WRLCK */
  int ofst,             /* Offset to first byte to be locked/unlocked */
  int nByte             /* Number of bytes to lock or unlock */
){
  OVERLAPPED ovlp;
  DWORD dwFlags;
  int rc = 0;           /* Result code form Lock/UnlockFileEx() */

  /* Access to the winShmNode object is serialized by the caller */
  Debug.Assert( sqlite3_mutex_held(pFile->mutex) || pFile->nRef==0 );

  /* Initialize the locking parameters */
  dwFlags = LOCKFILE_FAIL_IMMEDIATELY;
  if( lockType == _SHM_WRLCK ) dwFlags |= LOCKFILE_EXCLUSIVE_LOCK;

  memset(&ovlp, 0, sizeof(OVERLAPPED));
  ovlp.Offset = ofst;

  /* Release/Acquire the system-level lock */
  if( lockType==_SHM_UNLCK ){
    rc = UnlockFileEx(pFile->hFile.h, 0, nByte, 0, &ovlp);
  }else{
    rc = LockFileEx(pFile->hFile.h, dwFlags, 0, nByte, 0, &ovlp);
  }
  
  if( rc!= 0 ){
    rc = SQLITE_OK;
  }else{
    pFile->lastErrno =  GetLastError();
    rc = SQLITE_BUSY;
  }

  OSTRACE(("SHM-LOCK %d %s %s 0x%08lx\n", 
           pFile->hFile.h,
           rc==SQLITE_OK ? "ok" : "failed",
           lockType==_SHM_UNLCK ? "UnlockFileEx" : "LockFileEx",
           pFile->lastErrno));

  return rc;
}

/* Forward references to VFS methods */
static int winOpen(sqlite3_vfs*,const char*,sqlite3_file*,int,int);
static int winDelete(sqlite3_vfs *,const char*,int);

/*
** Purge the winShmNodeList list of all entries with winShmNode.nRef==0.
**
** This is not a VFS shared-memory method; it is a utility function called
** by VFS shared-memory methods.
*/
static void winShmPurge(sqlite3_vfs *pVfs, int deleteFlag){
  winShmNode **pp;
  winShmNode *p;
  BOOL bRc;
  Debug.Assert( winShmMutexHeld() );
  pp = winShmNodeList;
  while( (p = *pp)!=0 ){
    if( p->nRef==0 ){
      int i;
      if( p->mutex ) sqlite3_mutex_free(p->mutex);
      for(i=0; i<p->nRegion; i++){
        bRc = UnmapViewOfFile(p->aRegion[i].pMap);
        OSTRACE(("SHM-PURGE pid-%d unmap region=%d %s\n",
                 (int)GetCurrentProcessId(), i,
                 bRc ? "ok" : "failed"));
        bRc = CloseHandle(p->aRegion[i].hMap);
        OSTRACE(("SHM-PURGE pid-%d close region=%d %s\n",
                 (int)GetCurrentProcessId(), i,
                 bRc ? "ok" : "failed"));
      }
      if( p->hFile.h != INVALID_HANDLE_VALUE ){
        SimulateIOErrorBenign(1);
        winClose((sqlite3_file )&p->hFile);
        SimulateIOErrorBenign(0);
      }
      if( deleteFlag ){
        SimulateIOErrorBenign(1);
        winDelete(pVfs, p->zFilename, 0);
        SimulateIOErrorBenign(0);
      }
      *pp = p->pNext;
      sqlite3_free(p->aRegion);
      sqlite3_free(p);
    }else{
      pp = p->pNext;
    }
  }
}

/*
** Open the shared-memory area associated with database file pDbFd.
**
** When opening a new shared-memory file, if no other instances of that
** file are currently open, in this process or in other processes, then
** the file must be truncated to zero length or have its header cleared.
*/
static int winOpenSharedMemory(winFile *pDbFd){
  struct winShm *p;                  /* The connection to be opened */
  struct winShmNode *pShmNode = 0;   /* The underlying mmapped file */
  int rc;                            /* Result code */
  struct winShmNode *pNew;           /* Newly allocated winShmNode */
  int nName;                         /* Size of zName in bytes */

  Debug.Assert( pDbFd->pShm==null );    /* Not previously opened */

  /* Allocate space for the new sqlite3_shm object.  Also speculatively
  ** allocate space for a new winShmNode and filename.
  */
  p = sqlite3_malloc( sizeof(*p) );
  if( p==0 ) return SQLITE_NOMEM;
  memset(p, 0, sizeof(*p));
  nName = sqlite3Strlen30(pDbFd->zPath);
  pNew = sqlite3_malloc( sizeof(*pShmNode) + nName + 15 );
  if( pNew==0 ){
    sqlite3_free(p);
    return SQLITE_NOMEM;
  }
  memset(pNew, 0, sizeof(*pNew));
  pNew->zFilename = (char)&pNew[1];
  sqlite3_snprintf(nName+15, pNew->zFilename, "%s-shm", pDbFd->zPath);
  sqlite3FileSuffix3(pDbFd->zPath, pNew->zFilename); 

  /* Look to see if there is an existing winShmNode that can be used.
  ** If no matching winShmNode currently exists, create a new one.
  */
  winShmEnterMutex();
  for(pShmNode = winShmNodeList; pShmNode; pShmNode=pShmNode->pNext){
    /* TBD need to come up with better match here.  Perhaps
    ** use FILE_ID_BOTH_DIR_INFO Structure.
    */
    if( sqlite3StrICmp(pShmNode->zFilename, pNew->zFilename)==0 ) break;
  }
  if( pShmNode ){
    sqlite3_free(pNew);
  }else{
    pShmNode = pNew;
    pNew = 0;
    ((winFile)(&pShmNode->hFile))->h = INVALID_HANDLE_VALUE;
    pShmNode->pNext = winShmNodeList;
    winShmNodeList = pShmNode;

    pShmNode->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pShmNode->mutex==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }

    rc = winOpen(pDbFd->pVfs,
                 pShmNode->zFilename,             /* Name of the file (UTF-8) */
                 (sqlite3_file)&pShmNode->hFile,  /* File handle here */
                 SQLITE_OPEN_WAL | SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE, /* Mode flags */
                 0);
    if( SQLITE_OK!=rc ){
      rc = SQLITE_CANTOPEN_BKPT;
      goto shm_open_err;
    }

    /* Check to see if another process is holding the dead-man switch.
    ** If not, truncate the file to zero length. 
    */
    if( winShmSystemLock(pShmNode, _SHM_WRLCK, WIN_SHM_DMS, 1)==SQLITE_OK ){
      rc = winTruncate((sqlite3_file )&pShmNode->hFile, 0);
      if( rc!=SQLITE_OK ){
        rc = winLogError(SQLITE_IOERR_SHMOPEN, "winOpenShm", pDbFd->zPath);
      }
    }
    if( rc==SQLITE_OK ){
      winShmSystemLock(pShmNode, _SHM_UNLCK, WIN_SHM_DMS, 1);
      rc = winShmSystemLock(pShmNode, _SHM_RDLCK, WIN_SHM_DMS, 1);
    }
    if( rc ) goto shm_open_err;
  }

  /* Make the new connection a child of the winShmNode */
  p->pShmNode = pShmNode;
#if SQLITE_DEBUG
  p->id = pShmNode->nextShmId++;
#endif
  pShmNode->nRef++;
  pDbFd->pShm = p;
  winShmLeaveMutex();

  /* The reference count on pShmNode has already been incremented under
  ** the cover of the winShmEnterMutex() mutex and the pointer from the
  ** new (struct winShm) object to the pShmNode has been set. All that is
  ** left to do is to link the new object into the linked list starting
  ** at pShmNode->pFirst. This must be done while holding the pShmNode->mutex 
  ** mutex.
  */
  sqlite3_mutex_enter(pShmNode->mutex);
  p->pNext = pShmNode->pFirst;
  pShmNode->pFirst = p;
  sqlite3_mutex_leave(pShmNode->mutex);
  return SQLITE_OK;

  /* Jump here on any error */
shm_open_err:
  winShmSystemLock(pShmNode, _SHM_UNLCK, WIN_SHM_DMS, 1);
  winShmPurge(pDbFd->pVfs, 0);      /* This call frees pShmNode if required */
  sqlite3_free(p);
  sqlite3_free(pNew);
  winShmLeaveMutex();
  return rc;
}

/*
** Close a connection to shared-memory.  Delete the underlying 
** storage if deleteFlag is true.
*/
static int winShmUnmap(
  sqlite3_file *fd,          /* Database holding shared memory */
  int deleteFlag             /* Delete after closing if true */
){
  winFile *pDbFd;       /* Database holding shared-memory */
  winShm *p;            /* The connection to be closed */
  winShmNode *pShmNode; /* The underlying shared-memory file */
  winShm **pp;          /* For looping over sibling connections */

  pDbFd = (winFile)fd;
  p = pDbFd->pShm;
  if( p==0 ) return SQLITE_OK;
  pShmNode = p->pShmNode;

  /* Remove connection p from the set of connections associated
  ** with pShmNode */
  sqlite3_mutex_enter(pShmNode->mutex);
  for(pp=&pShmNode->pFirst; (*pp)!=p; pp = (*pp)->pNext){}
  *pp = p->pNext;

  /* Free the connection p */
  sqlite3_free(p);
  pDbFd->pShm = 0;
  sqlite3_mutex_leave(pShmNode->mutex);

  /* If pShmNode->nRef has reached 0, then close the underlying
  ** shared-memory file, too */
  winShmEnterMutex();
  Debug.Assert( pShmNode->nRef>0 );
  pShmNode->nRef--;
  if( pShmNode->nRef==0 ){
    winShmPurge(pDbFd->pVfs, deleteFlag);
  }
  winShmLeaveMutex();

  return SQLITE_OK;
}

/*
** Change the lock state for a shared-memory segment.
*/
static int winShmLock(
  sqlite3_file *fd,          /* Database file holding the shared memory */
  int ofst,                  /* First lock to acquire or release */
  int n,                     /* Number of locks to acquire or release */
  int flags                  /* What to do with the lock */
){
  winFile *pDbFd = (winFile)fd;        /* Connection holding shared memory */
  winShm *p = pDbFd->pShm;              /* The shared memory being locked */
  winShm *pX;                           /* For looping over all siblings */
  winShmNode *pShmNode = p->pShmNode;
  int rc = SQLITE_OK;                   /* Result code */
  u16 mask;                             /* Mask of locks to take or release */

  Debug.Assert( ofst>=0 && ofst+n<=SQLITE_SHM_NLOCK );
  Debug.Assert( n>=1 );
  Debug.Assert( flags==(SQLITE_SHM_LOCK | SQLITE_SHM_SHARED)
       || flags==(SQLITE_SHM_LOCK | SQLITE_SHM_EXCLUSIVE)
       || flags==(SQLITE_SHM_UNLOCK | SQLITE_SHM_SHARED)
       || flags==(SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE) );
  Debug.Assert( n==1 || (flags & SQLITE_SHM_EXCLUSIVE)!=0 );

  mask = (u16)((1U<<(ofst+n)) - (1U<<ofst));
  Debug.Assert( n>1 || mask==(1<<ofst) );
  sqlite3_mutex_enter(pShmNode->mutex);
  if( flags & SQLITE_SHM_UNLOCK ){
    u16 allMask = 0; /* Mask of locks held by siblings */

    /* See if any siblings hold this same lock */
    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
      if( pX==p ) continue;
      Debug.Assert( (pX->exclMask & (p->exclMask|p->sharedMask))==0 );
      allMask |= pX->sharedMask;
    }

    /* Unlock the system-level locks */
    if( (mask & allMask)==0 ){
      rc = winShmSystemLock(pShmNode, _SHM_UNLCK, ofst+WIN_SHM_BASE, n);
    }else{
      rc = SQLITE_OK;
    }

    /* Undo the local locks */
    if( rc==SQLITE_OK ){
      p->exclMask &= ~mask;
      p->sharedMask &= ~mask;
    } 
  }else if( flags & SQLITE_SHM_SHARED ){
    u16 allShared = 0;  /* Union of locks held by connections other than "p" */

    /* Find out which shared locks are already held by sibling connections.
    ** If any sibling already holds an exclusive lock, go ahead and return
    ** SQLITE_BUSY.
    */
    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
      if( (pX->exclMask & mask)!=0 ){
        rc = SQLITE_BUSY;
        break;
      }
      allShared |= pX->sharedMask;
    }

    /* Get shared locks at the system level, if necessary */
    if( rc==SQLITE_OK ){
      if( (allShared & mask)==0 ){
        rc = winShmSystemLock(pShmNode, _SHM_RDLCK, ofst+WIN_SHM_BASE, n);
      }else{
        rc = SQLITE_OK;
      }
    }

    /* Get the local shared locks */
    if( rc==SQLITE_OK ){
      p->sharedMask |= mask;
    }
  }else{
    /* Make sure no sibling connections hold locks that will block this
    ** lock.  If any do, return SQLITE_BUSY right away.
    */
    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
      if( (pX->exclMask & mask)!=0 || (pX->sharedMask & mask)!=0 ){
        rc = SQLITE_BUSY;
        break;
      }
    }
  
    /* Get the exclusive locks at the system level.  Then if successful
    ** also mark the local connection as being locked.
    */
    if( rc==SQLITE_OK ){
      rc = winShmSystemLock(pShmNode, _SHM_WRLCK, ofst+WIN_SHM_BASE, n);
      if( rc==SQLITE_OK ){
        Debug.Assert( (p->sharedMask & mask)==0 );
        p->exclMask |= mask;
      }
    }
  }
  sqlite3_mutex_leave(pShmNode->mutex);
  OSTRACE(("SHM-LOCK shmid-%d, pid-%d got %03x,%03x %s\n",
           p->id, (int)GetCurrentProcessId(), p->sharedMask, p->exclMask,
           rc ? "failed" : "ok"));
  return rc;
}

/*
** Implement a memory barrier or memory fence on shared memory.  
**
** All loads and stores begun before the barrier must complete before
** any load or store begun after the barrier.
*/
static void winShmBarrier(
  sqlite3_file *fd          /* Database holding the shared memory */
){
  UNUSED_PARAMETER(fd);
  /* MemoryBarrier(); // does not work -- do not know why not */
  winShmEnterMutex();
  winShmLeaveMutex();
}

/*
** This function is called to obtain a pointer to region iRegion of the 
** shared-memory associated with the database file fd. Shared-memory regions 
** are numbered starting from zero. Each shared-memory region is szRegion 
** bytes in size.
**
** If an error occurs, an error code is returned and *pp is set to NULL.
**
** Otherwise, if the isWrite parameter is 0 and the requested shared-memory
** region has not been allocated (by any client, including one running in a
** separate process), then *pp is set to NULL and SQLITE_OK returned. If 
** isWrite is non-zero and the requested shared-memory region has not yet 
** been allocated, it is allocated by this function.
**
** If the shared-memory region has already been allocated or is allocated by
** this call as described above, then it is mapped into this processes 
** address space (if it is not already), *pp is set to point to the mapped 
** memory and SQLITE_OK returned.
*/
static int winShmMap(
  sqlite3_file *fd,               /* Handle open on database file */
  int iRegion,                    /* Region to retrieve */
  int szRegion,                   /* Size of regions */
  int isWrite,                    /* True to extend file if necessary */
  void volatile **pp              /* OUT: Mapped memory */
){
  winFile *pDbFd = (winFile)fd;
  winShm *p = pDbFd->pShm;
  winShmNode *pShmNode;
  int rc = SQLITE_OK;

  if( null==p ){
    rc = winOpenSharedMemory(pDbFd);
    if( rc!=SQLITE_OK ) return rc;
    p = pDbFd->pShm;
  }
  pShmNode = p->pShmNode;

  sqlite3_mutex_enter(pShmNode->mutex);
  Debug.Assert( szRegion==pShmNode->szRegion || pShmNode->nRegion==0 );

  if( pShmNode->nRegion<=iRegion ){
    struct ShmRegion *apNew;           /* New aRegion[] array */
    int nByte = (iRegion+1)*szRegion;  /* Minimum required file size */
    sqlite3_int64 sz;                  /* Current size of wal-index file */

    pShmNode->szRegion = szRegion;

    /* The requested region is not mapped into this processes address space.
    ** Check to see if it has been allocated (i.e. if the wal-index file is
    ** large enough to contain the requested region).
    */
    rc = winFileSize((sqlite3_file )&pShmNode->hFile, &sz);
    if( rc!=SQLITE_OK ){
      rc = winLogError(SQLITE_IOERR_SHMSIZE, "winShmMap1", pDbFd->zPath);
      goto shmpage_out;
    }

    if( sz<nByte ){
      /* The requested memory region does not exist. If isWrite is set to
      ** zero, exit early. *pp will be set to NULL and SQLITE_OK returned.
      **
      ** Alternatively, if isWrite is non-zero, use ftruncate() to allocate
      ** the requested memory region.
      */
      if( null==isWrite ) goto shmpage_out;
      rc = winTruncate((sqlite3_file )&pShmNode->hFile, nByte);
      if( rc!=SQLITE_OK ){
        rc = winLogError(SQLITE_IOERR_SHMSIZE, "winShmMap2", pDbFd->zPath);
        goto shmpage_out;
      }
    }

    /* Map the requested memory region into this processes address space. */
    apNew = (struct ShmRegion )sqlite3_realloc(
        pShmNode->aRegion, (iRegion+1)*sizeof(apNew[0])
    );
    if( null==apNew ){
      rc = SQLITE_IOERR_NOMEM;
      goto shmpage_out;
    }
    pShmNode->aRegion = apNew;

    while( pShmNode->nRegion<=iRegion ){
      HANDLE hMap;                /* file-mapping handle */
      void *pMap = 0;             /* Mapped memory region */
     
      hMap = CreateFileMapping(pShmNode->hFile.h, 
          NULL, PAGE_READWRITE, 0, nByte, NULL
      );
      OSTRACE(("SHM-MAP pid-%d create region=%d nbyte=%d %s\n",
               (int)GetCurrentProcessId(), pShmNode->nRegion, nByte,
               hMap ? "ok" : "failed"));
      if( hMap ){
        int iOffset = pShmNode->nRegion*szRegion;
        int iOffsetShift = iOffset % winSysInfo.dwAllocationGranularity;
        pMap = MapViewOfFile(hMap, FILE_MAP_WRITE | FILE_MAP_READ,
            0, iOffset - iOffsetShift, szRegion + iOffsetShift
        );
        OSTRACE(("SHM-MAP pid-%d map region=%d offset=%d size=%d %s\n",
                 (int)GetCurrentProcessId(), pShmNode->nRegion, iOffset, szRegion,
                 pMap ? "ok" : "failed"));
      }
      if( null==pMap ){
        pShmNode->lastErrno = GetLastError();
        rc = winLogError(SQLITE_IOERR_SHMMAP, "winShmMap3", pDbFd->zPath);
        if( hMap ) CloseHandle(hMap);
        goto shmpage_out;
      }

      pShmNode->aRegion[pShmNode->nRegion].pMap = pMap;
      pShmNode->aRegion[pShmNode->nRegion].hMap = hMap;
      pShmNode->nRegion++;
    }
  }

shmpage_out:
  if( pShmNode->nRegion>iRegion ){
    int iOffset = iRegion*szRegion;
    int iOffsetShift = iOffset % winSysInfo.dwAllocationGranularity;
    char *p = (char )pShmNode->aRegion[iRegion].pMap;
    *pp = (void )&p[iOffsetShift];
  }else{
    *pp = 0;
  }
  sqlite3_mutex_leave(pShmNode->mutex);
  return rc;
}

#else
    //# define winShmMap     0
    static int winShmMap(
    sqlite3_file fd,                /* Handle open on database file */
    int iRegion,                    /* Region to retrieve */
    int szRegion,                   /* Size of regions */
    int isWrite,                    /* True to extend file if necessary */
    out object pp                   /* OUT: Mapped memory */
    )
    {
      pp = null;
      return 0;
    }

    //# define winShmLock    0
    static int winShmLock(
    sqlite3_file fd,           /* Database file holding the shared memory */
    int ofst,                  /* First lock to acquire or release */
    int n,                     /* Number of locks to acquire or release */
    int flags                  /* What to do with the lock */
    )
    {
      return 0;
    }

    //# define winShmBarrier 0
    static void winShmBarrier(
    sqlite3_file fd          /* Database holding the shared memory */
    )
    {
    }

    //# define winShmUnmap   0
    static int winShmUnmap(
    sqlite3_file fd,           /* Database holding shared memory */
    int deleteFlag             /* Delete after closing if true */
    )
    {
      return 0;
    }

#endif //* #if !SQLITE_OMIT_WAL */

    /*
** Here ends the implementation of all sqlite3_file methods.
**
********************** End sqlite3_file Methods *******************************
******************************************************************************/

    /*
    ** This vector defines all the methods that can operate on an
    ** sqlite3_file for win32.
    */
    static sqlite3_io_methods winIoMethod = new sqlite3_io_methods(
    2,                                                  /* iVersion */
    (dxClose)winClose,                                  /* xClose */
    (dxRead)winRead,                                    /* xRead */
    (dxWrite)winWrite,                                  /* xWrite */
    (dxTruncate)winTruncate,                            /* xTruncate */
    (dxSync)winSync,                                    /* xSync */
    (dxFileSize)winFileSize,                            /* xFileSize */
    (dxLock)winLock,                                    /* xLock */
    (dxUnlock)winUnlock,                                /* xUnlock */
    (dxCheckReservedLock)winCheckReservedLock,          /* xCheckReservedLock */
    (dxFileControl)winFileControl,                      /* xFileControl */
    (dxSectorSize)winSectorSize,                        /* xSectorSize */
    (dxDeviceCharacteristics)winDeviceCharacteristics,  /* xDeviceCharacteristics */
    (dxShmMap)winShmMap,                                /* xShmMap */
    (dxShmLock)winShmLock,                              /* xShmLock */
    (dxShmBarrier)winShmBarrier,                        /* xShmBarrier */
    (dxShmUnmap)winShmUnmap                             /* xShmUnmap */
    );

    /****************************************************************************
    **************************** sqlite3_vfs methods ****************************
    **
    ** This division contains the implementation of methods on the
    ** sqlite3_vfs object.
    */

    /*
    ** Convert a UTF-8 filename into whatever form the underlying
    ** operating system wants filenames in.  Space to hold the result
    ** is obtained from malloc and must be freed by the calling
    ** function.
    */
    static string convertUtf8Filename( string zFilename )
    {
      return zFilename;
      // string zConverted = "";
      //if (isNT())
      //{
      //  zConverted = utf8ToUnicode(zFilename);
      /* isNT() is 1 if SQLITE_OS_WINCE==1, so this else is never executed.
      */
#if !SQLITE_OS_WINCE
      //}
      //else
      //{
      //  zConverted = sqlite3_win32_utf8_to_mbcs(zFilename);
#endif
      //}
      /* caller will handle out of memory */
      //return zConverted;
    }

    /*
    ** Create a temporary file name in zBuf.  zBuf must be big enough to
    ** hold at pVfs.mxPathname characters.
    */
    static int getTempname( int nBuf, StringBuilder zBuf )
    {
      const string zChars = "abcdefghijklmnopqrstuvwxyz0123456789";
      //static char zChars[] =
      //  "abcdefghijklmnopqrstuvwxyz"
      //  "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
      //  "0123456789";
      //size_t i, j;
      //char zTempPath[MAX_PATH+1];

      /* It's odd to simulate an io-error here, but really this is just
      ** using the io-error infrastructure to test that SQLite handles this
      ** function failing. 
      */
#if SQLITE_TEST
      if ( SimulateIOError() )
        return SQLITE_IOERR;
#endif

      //if( sqlite3_temp_directory ){
      //  sqlite3_snprintf(MAX_PATH-30, zTempPath, "%s", sqlite3_temp_directory);
      //}else if( isNT() ){
      //  string zMulti;
      //  WCHAR zWidePath[MAX_PATH];
      //  GetTempPathW(MAX_PATH-30, zWidePath);
      //  zMulti = unicodeToUtf8(zWidePath);
      //  if( zMulti ){
      //    sqlite3_snprintf(MAX_PATH-30, zTempPath, "%s", zMulti);
      //    free(zMulti);
      //  }else{
      //    return SQLITE_NOMEM;
      //  }
      /* isNT() is 1 if SQLITE_OS_WINCE==1, so this else is never executed.
      ** Since the ASCII version of these Windows API do not exist for WINCE,
      ** it's important to not reference them for WINCE builds.
      */
#if !SQLITE_OS_WINCE
      //}else{
      //  string zUtf8;
      //  char zMbcsPath[MAX_PATH];
      //  GetTempPathA(MAX_PATH-30, zMbcsPath);
      //  zUtf8 = sqlite3_win32_mbcs_to_utf8(zMbcsPath);
      //  if( zUtf8 ){
      //    sqlite3_snprintf(MAX_PATH-30, zTempPath, "%s", zUtf8);
      //    free(zUtf8);
      //  }else{
      //    return SQLITE_NOMEM;
      //  }
#endif
      //}

      /* Check that the output buffer is large enough for the temporary file 
      ** name. If it is not, return SQLITE_ERROR.
      */
      //if( (sqlite3Strlen30(zTempPath) + sqlite3Strlen30(SQLITE_TEMP_FILE_PREFIX) + 17) >= nBuf ){
      //  return SQLITE_ERROR;
      //}

      StringBuilder zRandom = new StringBuilder( 20 );
      i64 iRandom = 0;
      for ( int i = 0; i < 15; i++ )
      {
        sqlite3_randomness( 1, ref iRandom );
        zRandom.Append( (char)zChars[(int)( iRandom % ( zChars.Length - 1 ) )] );
      }
      //  zBuf[j] = 0;
#if SQLITE_WINRT
      zBuf.Append( Path.Combine(ApplicationData.Current.LocalFolder.Path, SQLITE_TEMP_FILE_PREFIX + zRandom.ToString()) );
#else
      zBuf.Append( Path.GetTempPath() + SQLITE_TEMP_FILE_PREFIX + zRandom.ToString() );
#endif
      //for(i=sqlite3Strlen30(zTempPath); i>0 && zTempPath[i-1]=='\\'; i--){}
      //zTempPath[i] = 0;
      //sqlite3_snprintf(nBuf-17, zBuf,
      //                 "%s\\"SQLITE_TEMP_FILE_PREFIX, zTempPath);
      //j = sqlite3Strlen30(zBuf);
      //sqlite3_randomness(15, zBuf[j]);
      //for(i=0; i<15; i++, j++){
      //  zBuf[j] = (char)zChars[ ((unsigned char)zBuf[j])%(sizeof(zChars)-1) ];
      //}
      //zBuf[j] = 0;

#if SQLITE_DEBUG
      OSTRACE( "TEMP FILENAME: %s\n", zBuf.ToString() );
#endif
      return SQLITE_OK;
    }

    /*
    ** Open a file.
    */
    static int winOpen(
    sqlite3_vfs pVfs,       /* Not used */
    string zName,           /* Name of the file (UTF-8) */
    sqlite3_file pFile, /* Write the SQLite file handle here */
    int flags,              /* Open mode flags */
    out int pOutFlags       /* Status return flags */
    )
    {
      //HANDLE h;
#if SQLITE_WINRT
        IRandomAccessStream fs = null;
      DWORD dwDesiredAccess = 0;
#else
      FileStream fs = null;
      FileAccess dwDesiredAccess;
      FileShare dwShareMode;
      FileMode dwCreationDisposition;
#endif
#if !(SQLITE_SILVERLIGHT || WINDOWS_MOBILE || SQLITE_WINRT)
      FileOptions dwFlagsAndAttributes;
#endif
#if SQLITE_OS_WINCE
int isTemp = 0;
#endif
      //winFile* pFile = (winFile)id;
      string zConverted;                 /* Filename in OS encoding */
      string zUtf8Name = zName;    /* Filename in UTF-8 encoding */
      pOutFlags = 0;

      /* If argument zPath is a NULL pointer, this function is required to open
      ** a temporary file. Use this buffer to store the file name in.
      */
      StringBuilder zTmpname = new StringBuilder( MAX_PATH + 1 );        /* Buffer used to create temp filename */

      int rc = SQLITE_OK;            /* Function Return Code */
      int eType = (int)( flags & 0xFFFFFF00 );  /* Type of file to open */
      bool isExclusive = ( flags & SQLITE_OPEN_EXCLUSIVE ) != 0;
      bool isDelete = ( flags & SQLITE_OPEN_DELETEONCLOSE ) != 0;
      bool isCreate = ( flags & SQLITE_OPEN_CREATE ) != 0;
      bool isReadonly = ( flags & SQLITE_OPEN_READONLY ) != 0;
      bool isReadWrite = ( flags & SQLITE_OPEN_READWRITE ) != 0;
      bool isOpenJournal = ( isCreate && (
      eType == SQLITE_OPEN_MASTER_JOURNAL
      || eType == SQLITE_OPEN_MAIN_JOURNAL
      || eType == SQLITE_OPEN_WAL
      ) );

      /* Check the following statements are true:
**
**   (a) Exactly one of the READWRITE and READONLY flags must be set, and
**   (b) if CREATE is set, then READWRITE must also be set, and
**   (c) if EXCLUSIVE is set, then CREATE must also be set.
**   (d) if DELETEONCLOSE is set, then CREATE must also be set.
*/
      Debug.Assert( ( isReadonly == false || isReadWrite == false ) && ( isReadWrite || isReadonly ) );
      Debug.Assert( isCreate == false || isReadWrite );
      Debug.Assert( isExclusive == false || isCreate );
      Debug.Assert( isDelete == false || isCreate );

      /* The main DB, main journal, WAL file and master journal are never
      ** automatically deleted. Nor are they ever temporary files.  */
      //Debug.Assert( ( !isDelete && !String.IsNullOrEmpty(zName) ) || eType != SQLITE_OPEN_MAIN_DB );
      Debug.Assert( ( !isDelete && !String.IsNullOrEmpty( zName ) ) || eType != SQLITE_OPEN_MAIN_JOURNAL );
      Debug.Assert( ( !isDelete && !String.IsNullOrEmpty( zName ) ) || eType != SQLITE_OPEN_MASTER_JOURNAL );
      Debug.Assert( ( !isDelete && !String.IsNullOrEmpty( zName ) ) || eType != SQLITE_OPEN_WAL );

      /* Assert that the upper layer has set one of the "file-type" flags. */
      Debug.Assert( eType == SQLITE_OPEN_MAIN_DB || eType == SQLITE_OPEN_TEMP_DB
      || eType == SQLITE_OPEN_MAIN_JOURNAL || eType == SQLITE_OPEN_TEMP_JOURNAL
      || eType == SQLITE_OPEN_SUBJOURNAL || eType == SQLITE_OPEN_MASTER_JOURNAL
      || eType == SQLITE_OPEN_TRANSIENT_DB || eType == SQLITE_OPEN_WAL
      );

      //assert( id!=0 );
      UNUSED_PARAMETER( pVfs );

      pFile.fs = null;//.h = INVALID_HANDLE_VALUE;

      /* If the second argument to this function is NULL, generate a
      ** temporary file name to use
      */
      if ( String.IsNullOrEmpty( zUtf8Name ) )
      {
        Debug.Assert( isDelete && !isOpenJournal );
        rc = getTempname( MAX_PATH + 1, zTmpname );
        if ( rc != SQLITE_OK )
        {
          return rc;
        }
        zUtf8Name = zTmpname.ToString();
      }

      // /* Convert the filename to the system encoding. */
      zConverted = zUtf8Name;// convertUtf8Filename( zUtf8Name );
      //if ( zConverted.StartsWith( "/", StringComparison.Ordinal ) && !zConverted.StartsWith( "//", StringComparison.Ordinal ) )
      //  zConverted = zConverted.Substring( 1 );
      //if ( String.IsNullOrEmpty( zConverted ) )
      //{
      //  return SQLITE_NOMEM;
      //}
#if !SQLITE_WINRT
      if ( isReadWrite )
      {
        dwDesiredAccess = FileAccess.Read | FileAccess.Write; // GENERIC_READ | GENERIC_WRITE;
      }
      else
      {
        dwDesiredAccess = FileAccess.Read; // GENERIC_READ;
      }

      /* SQLITE_OPEN_EXCLUSIVE is used to make sure that a new file is
      ** created. SQLite doesn't use it to indicate "exclusive access"
      ** as it is usually understood.
      */
      if ( isExclusive )
      {
        /* Creates a new file, only if it does not already exist. */
        /* If the file exists, it fails. */
        dwCreationDisposition = FileMode.CreateNew;// CREATE_NEW;
      }
      else if ( isCreate )
      {
        /* Open existing file, or create if it doesn't exist */
        dwCreationDisposition = FileMode.OpenOrCreate;// OPEN_ALWAYS;
      }
      else
      {
        /* Opens a file, only if it exists. */
        dwCreationDisposition = FileMode.Open;//OPEN_EXISTING;
      }

      dwShareMode = FileShare.Read | FileShare.Write;// FILE_SHARE_READ | FILE_SHARE_WRITE;
#endif
      if ( isDelete )
      {
#if SQLITE_OS_WINCE
dwFlagsAndAttributes = FILE_ATTRIBUTE_HIDDEN;
isTemp = 1;
#else
#if !(SQLITE_SILVERLIGHT || WINDOWS_MOBILE || SQLITE_WINRT)
        dwFlagsAndAttributes = FileOptions.DeleteOnClose; // FILE_ATTRIBUTE_TEMPORARY
        //| FILE_ATTRIBUTE_HIDDEN
        //| FILE_FLAG_DELETE_ON_CLOSE;
#endif
#endif
      }
      else
      {
#if !(SQLITE_SILVERLIGHT || WINDOWS_MOBILE || SQLITE_WINRT)
        dwFlagsAndAttributes = FileOptions.None; // FILE_ATTRIBUTE_NORMAL;
#endif
      }
      /* Reports from the internet are that performance is always
      ** better if FILE_FLAG_RANDOM_ACCESS is used.  Ticket #2699. */
#if SQLITE_OS_WINCE
dwFlagsAndAttributes |= FileOptions.RandomAccess; // FILE_FLAG_RANDOM_ACCESS;
#endif

      if ( isNT() )
      {
        //h = CreateFileW((WCHAR)zConverted,
        //   dwDesiredAccess,
        //   dwShareMode,
        //   NULL,
        //   dwCreationDisposition,
        //   dwFlagsAndAttributes,
        //   NULL
        //);

        //
        // retry opening the file a few times; this is because of a racing condition between a delete and open call to the FS
        //
        int retries = 3;
        while ( ( fs == null ) && ( retries > 0 ) )
          try
          {
            retries--;
#if SQLITE_WINRT

            Task<StorageFile> fileTask = null;
            if(isExclusive)
            {
                if(HelperMethods.FileExists(zConverted))
                {
                    // Error
                    throw new IOException("file already exists");
                }
                else
                {
                    Task<StorageFolder> folderTask = StorageFolder.GetFolderFromPathAsync(Path.GetDirectoryName(zConverted)).AsTask<StorageFolder>();
                    folderTask.Wait();
                    fileTask = folderTask.Result.CreateFileAsync(Path.GetFileName(zConverted)).AsTask<StorageFile>();
                }
            }
            else if (isCreate)
            {
                if (HelperMethods.FileExists(zConverted))
                {
                    fileTask = StorageFile.GetFileFromPathAsync(zConverted).AsTask<StorageFile>();
                }
                else
                {
                    Task<StorageFolder> folderTask = StorageFolder.GetFolderFromPathAsync(Path.GetDirectoryName(zConverted)).AsTask<StorageFolder>();
                    folderTask.Wait();
                    fileTask = folderTask.Result.CreateFileAsync(Path.GetFileName(zConverted)).AsTask<StorageFile>();
                }
            }
            else
            {
                fileTask = StorageFile.GetFileFromPathAsync(zConverted).AsTask<StorageFile>();
            }
            fileTask.Wait();
            Task<IRandomAccessStream> streamTask = fileTask.Result.OpenAsync(FileAccessMode.ReadWrite).AsTask<IRandomAccessStream>();
            streamTask.Wait();
            fs = streamTask.Result;
#elif WINDOWS_PHONE || SQLITE_SILVERLIGHT  
 fs = new IsolatedStorageFileStream(zConverted, dwCreationDisposition, dwDesiredAccess, dwShareMode, IsolatedStorageFile.GetUserStoreForApplication());
#elif !(SQLITE_SILVERLIGHT || WINDOWS_MOBILE)
            fs = new FileStream( zConverted, dwCreationDisposition, dwDesiredAccess, dwShareMode, 4096, dwFlagsAndAttributes );
#else
            fs = new FileStream( zConverted, dwCreationDisposition, dwDesiredAccess, dwShareMode, 4096);
#endif

#if SQLITE_DEBUG
#if WINDOWS_PHONE || SQLITE_SILVERLIGHT
            OSTRACE( "OPEN %d (%s)\n", fs.GetHashCode(), zName );
#else
            OSTRACE("OPEN %d (%s)\n", fs.GetHashCode(), fs.Name);
#endif
#endif
          }
          catch ( Exception e )
          {
#if SQLITE_WINRT
              System.Threading.Tasks.Task.Delay(100).Wait();

#else
              Thread.Sleep(100);
#endif
          }

        /* isNT() is 1 if SQLITE_OS_WINCE==1, so this else is never executed.
        ** Since the ASCII version of these Windows API do not exist for WINCE,
        ** it's important to not reference them for WINCE builds.
        */
#if !SQLITE_OS_WINCE
      }
      else
      {
        Debugger.Break(); // Not NT
        //h = CreateFileA((char)zConverted,
        //   dwDesiredAccess,
        //   dwShareMode,
        //   NULL,
        //   dwCreationDisposition,
        //   dwFlagsAndAttributes,
        //   NULL
        //);
#endif
      }

      OSTRACE( "OPEN %d %s 0x%lx %s\n",
      pFile.GetHashCode(), zName, dwDesiredAccess,
      fs == null ? "failed" : "ok" );
      if ( fs == null
      ||
#if !(SQLITE_SILVERLIGHT || WINDOWS_MOBILE || SQLITE_WINRT)
 fs.SafeFileHandle.IsInvalid
#else
 !fs.CanRead
#endif
 ) //(h == INVALID_HANDLE_VALUE)
      {
#if SQLITE_SILVERLIGHT || SQLITE_WINRT
          pFile.lastErrno = 1;
#else
        //      pFile.lastErrno = GetLastError();
        pFile.lastErrno = (u32)HelperMethods.GetLastError();
#endif
      winLogError(SQLITE_CANTOPEN, "winOpen", zUtf8Name);
        //        free(zConverted);
        if ( isReadWrite )
        {
          return winOpen( pVfs, zName, pFile,
          ( ( flags | SQLITE_OPEN_READONLY ) & ~( SQLITE_OPEN_CREATE | SQLITE_OPEN_READWRITE ) ), out pOutFlags );
        }
        else
        {
          return SQLITE_CANTOPEN_BKPT();
        }
      }

      //if ( pOutFlags )
      //{
      if ( isReadWrite )
      {
        pOutFlags = SQLITE_OPEN_READWRITE;
      }
      else
      {
        pOutFlags = SQLITE_OPEN_READONLY;
      }
      //}

      pFile.Clear(); // memset(pFile, 0, sizeof(*pFile));
      pFile.pMethods = winIoMethod;
      pFile.fs = fs;
      pFile.lastErrno = NO_ERROR;
      pFile.pVfs = pVfs;
      pFile.pShm = null;
      pFile.zPath = zName;
      pFile.sectorSize = (ulong)getSectorSize( pVfs, zUtf8Name );
#if SQLITE_OS_WINCE
if( isReadWrite && eType==SQLITE_OPEN_MAIN_DB
&& !winceCreateLock(zName, pFile)
){
CloseHandle(h);
free(zConverted);
return SQLITE_CANTOPEN_BKPT;
}
if( isTemp ){
pFile.zDeleteOnClose = zConverted;
}else
#endif
      {
        // free(zConverted);
      }

#if SQLITE_TEST
      OpenCounter( +1 );
#endif
      return rc;
    }

    /*
    ** Delete the named file.
    **
    ** Note that windows does not allow a file to be deleted if some other
    ** process has it open.  Sometimes a virus scanner or indexing program
    ** will open a journal file shortly after it is created in order to do
    ** whatever it does.  While this other process is holding the
    ** file open, we will be unable to delete it.  To work around this
    ** problem, we delay 100 milliseconds and try to delete again.  Up
    ** to MX_DELETION_ATTEMPTs deletion attempts are run before giving
    ** up and returning an error.
    */
    static int MX_DELETION_ATTEMPTS = 5;
    static int winDelete(
    sqlite3_vfs pVfs,         /* Not used on win32 */
    string zFilename,         /* Name of file to delete */
    int syncDir               /* Not used on win32 */
    )
    {
      int cnt = 0;
      int rc = SQLITE_ERROR;
      int error;
      string zConverted;
      UNUSED_PARAMETER( pVfs );
      UNUSED_PARAMETER( syncDir );

#if SQLITE_TEST
      if ( SimulateIOError() )
        return SQLITE_IOERR_DELETE;
#endif
      zConverted = convertUtf8Filename( zFilename );
      //if ( zConverted == null || zConverted == "" )
      //{
      //  return SQLITE_NOMEM;
      //}
      if ( isNT() )
      {
        do
        //  DeleteFileW(zConverted);
        //}while(   (   ((rc = GetFileAttributesW(zConverted)) != INVALID_FILE_ATTRIBUTES)
        //           || ((error = GetLastError()) == ERROR_ACCESS_DENIED))
        //       && (++cnt < MX_DELETION_ATTEMPTS)
        //       && (Sleep(100), 1) );
        {
#if SQLITE_WINRT
            if(!HelperMethods.FileExists(zFilename))
#elif WINDOWS_PHONE
           if ( !System.IO.IsolatedStorage.IsolatedStorageFile.GetUserStoreForApplication().FileExists( zFilename ) )
#else
          if ( !File.Exists( zFilename ) )
#endif
          {
            rc = SQLITE_IOERR;
            break;
          }
          try
          {
#if SQLITE_WINRT
              Task<StorageFile> fileTask = StorageFile.GetFileFromPathAsync(zConverted).AsTask<StorageFile>();
              fileTask.Wait();
              fileTask.Result.DeleteAsync().AsTask().Wait();
#elif WINDOWS_PHONE
              System.IO.IsolatedStorage.IsolatedStorageFile.GetUserStoreForApplication().DeleteFile(zFilename);
#elif SQLITE_SILVERLIGHT
              IsolatedStorageFile.GetUserStoreForApplication().DeleteFile(zFilename);
#else
            File.Delete( zConverted );
#endif
            rc = SQLITE_OK;
          }
          catch ( IOException e )
          {
            rc = SQLITE_IOERR;
#if SQLITE_WINRT
            System.Threading.Tasks.Task.Delay(100).Wait();

#else
            Thread.Sleep(100);
#endif
          }
        } while ( rc != SQLITE_OK && ++cnt < MX_DELETION_ATTEMPTS );
        /* isNT() is 1 if SQLITE_OS_WINCE==1, so this else is never executed.
        ** Since the ASCII version of these Windows API do not exist for WINCE,
        ** it's important to not reference them for WINCE builds.
        */
#if !SQLITE_OS_WINCE && !SQLITE_WINRT
      }
      else
      {
        do
        {
          //DeleteFileA( zConverted );
          //}while(   (   ((rc = GetFileAttributesA(zConverted)) != INVALID_FILE_ATTRIBUTES)
          //           || ((error = GetLastError()) == ERROR_ACCESS_DENIED))
          //       && (cnt++ < MX_DELETION_ATTEMPTS)
          //       && (Sleep(100), 1) );
          if ( !File.Exists( zFilename ) )
          {
            rc = SQLITE_IOERR;
            break;
          }
          try
          {
            File.Delete( zConverted );
            rc = SQLITE_OK;
          }
          catch ( IOException e )
          {
            rc = SQLITE_IOERR;
            Thread.Sleep( 100 );
          }
        } while ( rc != SQLITE_OK && cnt++ < MX_DELETION_ATTEMPTS );
#endif
      }
      //free(zConverted);
#if SQLITE_DEBUG
      OSTRACE( "DELETE \"%s\"\n", zFilename );
#endif
      if ( rc == SQLITE_OK )
        return rc;

      error = HelperMethods.GetLastError();

      return ( ( rc == INVALID_FILE_ATTRIBUTES )
        && ( error == ERROR_FILE_NOT_FOUND ) ) ? SQLITE_OK :
      winLogError(SQLITE_IOERR_DELETE, "winDelete", zFilename);
    }

    /*
    ** Check the existence and status of a file.
    */
    static int winAccess(
    sqlite3_vfs pVfs,       /* Not used on win32 */
    string zFilename,       /* Name of file to check */
    int flags,              /* Type of test to make on this file */
    out int pResOut         /* OUT: Result */
    )
    {
      FileAttributes attr = 0; // DWORD attr;
      int rc = 0;
      //  void *zConverted;
      UNUSED_PARAMETER( pVfs );

#if SQLITE_TEST
      if ( SimulateIOError() )
      {
        pResOut = -1;
        return SQLITE_IOERR_ACCESS;
      }
#endif
      //zConverted = convertUtf8Filename(zFilename);
      //  if( zConverted==0 ){
      //    return SQLITE_NOMEM;
      //  }
      //if ( isNT() )
      //{
      //
      // Do a quick test to prevent the try/catch block
      if ( flags == SQLITE_ACCESS_EXISTS )
      {
#if SQLITE_WINRT
          pResOut = HelperMethods.FileExists(zFilename) ? 1 : 0;
#elif WINDOWS_PHONE
          pResOut = System.IO.IsolatedStorage.IsolatedStorageFile.GetUserStoreForApplication().FileExists(zFilename) ? 1 : 0;
#elif SQLITE_SILVERLIGHT
          pResOut = IsolatedStorageFile.GetUserStoreForApplication().FileExists(zFilename) ? 1 : 0;
#else
        pResOut = File.Exists( zFilename ) ? 1 : 0;
#endif
        return SQLITE_OK;
      }
      //
      try
      {
          //WIN32_FILE_ATTRIBUTE_DATA sAttrData;
          //memset(&sAttrData, 0, sizeof(sAttrData));
          //if( GetFileAttributesExW((WCHAR)zConverted,
          //                         GetFileExInfoStandard, 
          //                         &sAttrData) ){
          //  /* For an SQLITE_ACCESS_EXISTS query, treat a zero-length file
          //  ** as if it does not exist.
          //  */
          //  if(    flags==SQLITE_ACCESS_EXISTS
          //      && sAttrData.nFileSizeHigh==0 
          //      && sAttrData.nFileSizeLow==0 ){
          //    attr = INVALID_FILE_ATTRIBUTES;
          //  }else{
          //    attr = sAttrData.dwFileAttributes;
          //  }
          //}else{
          //  if( GetLastError()!=ERROR_FILE_NOT_FOUND ){
          //    winLogError(SQLITE_IOERR_ACCESS, "winAccess", zFilename);
          //    free(zConverted);
          //    return SQLITE_IOERR_ACCESS;
          //  }else{
          //    attr = INVALID_FILE_ATTRIBUTES;
          //  }
          //}
#if SQLITE_WINRT
          attr = FileAttributes.Normal;
      }
#else
#if WINDOWS_MOBILE
        if (new DirectoryInfo(zFilename).Exists)
#elif SQLITE_WINRT
        if (HelperMethods.DirectoryExists(zFilename))
#elif WINDOWS_PHONE || SQLITE_SILVERLIGHT
        if (System.IO.IsolatedStorage.IsolatedStorageFile.GetUserStoreForApplication().DirectoryExists(zFilename))
#else
        if (Directory.Exists( zFilename ))
#endif
        {
          try
          {
            var tempName = new StringBuilder();
            getTempname(MAX_PATH + 1, tempName);
            string name = Path.Combine(zFilename, Path.GetFileNameWithoutExtension(tempName.ToString()));

#if SQLITE_WINRT
            Task<StorageFolder> fileTask = StorageFolder.GetFolderFromPathAsync(path).AsTask<StorageFolder>();
            fileTask.Wait();
            attr = fileTask.Attributes;
#elif WINDOWS_PHONE || SQLITE_SILVERLIGHT
            var stream = IsolatedStorageFile.GetUserStoreForApplication().CreateFile(name);
            stream.Close();
            IsolatedStorageFile.GetUserStoreForApplication().DeleteFile(name);
#else
            FileStream fs = File.Create( name );
            fs.Close();
            File.Delete( name );
#endif
            attr = FileAttributes.Normal;
          }
          catch ( IOException e )
          {
            attr = FileAttributes.ReadOnly;
          }
        }
      }
      /* isNT() is 1 if SQLITE_OS_WINCE==1, so this else is never executed.
      ** Since the ASCII version of these Windows API do not exist for WINCE,
      ** it's important to not reference them for WINCE builds.
      */
#if !SQLITE_OS_WINCE
      //}
      //else
      //{
      //  attr = GetFileAttributesA( (char)zConverted );
#endif
#endif
      //}
      catch ( IOException e )
      {
        winLogError(SQLITE_IOERR_ACCESS, "winAccess", zFilename);
      }
      //  free(zConverted);
      switch ( flags )
      {
        case SQLITE_ACCESS_READ:
        case SQLITE_ACCESS_EXISTS:
#if SQLITE_WINRT  
          rc = attr == FileAttributes.Normal ? 1 : 0;// != INVALID_FILE_ATTRIBUTES;
#else
          rc = attr != 0 ? 1 : 0;// != INVALID_FILE_ATTRIBUTES;
#endif
          break;
        case SQLITE_ACCESS_READWRITE:
#if SQLITE_WINRT  
          rc = attr != FileAttributes.Normal ? 0 : (int)( attr & FileAttributes.ReadOnly ) != 0 ? 0 : 1; //FILE_ATTRIBUTE_READONLY ) == 0;
#else
          rc = attr == 0 ? 0 : (int)( attr & FileAttributes.ReadOnly ) != 0 ? 0 : 1; //FILE_ATTRIBUTE_READONLY ) == 0;
#endif
          break;
        default:
          Debug.Assert( "" == "Invalid flags argument" );
          rc = 0;
          break;
      }
      pResOut = rc;
      return SQLITE_OK;
    }

    /*
    ** Turn a relative pathname into a full pathname.  Write the full
    ** pathname into zOut[].  zOut[] will be at least pVfs.mxPathname
    ** bytes in size.
    */
    static int winFullPathname(
    sqlite3_vfs pVfs,             /* Pointer to vfs object */
    string zRelative,             /* Possibly relative input path */
    int nFull,                    /* Size of output buffer in bytes */
    StringBuilder zFull           /* Output buffer */
    )
    {

#if __CYGWIN__
SimulateIOError( return SQLITE_ERROR );
UNUSED_PARAMETER(nFull);
cygwin_conv_to_full_win32_path(zRelative, zFull);
return SQLITE_OK;
#endif

#if SQLITE_OS_WINCE
SimulateIOError( return SQLITE_ERROR );
UNUSED_PARAMETER(nFull);
/* WinCE has no concept of a relative pathname, or so I am told. */
sqlite3_snprintf(pVfs.mxPathname, zFull, "%s", zRelative);
return SQLITE_OK;
#endif

#if !SQLITE_OS_WINCE && !__CYGWIN__
      int nByte;
      //string  zConverted;
      string zOut = null;

      /* If this path name begins with "/X:", where "X" is any alphabetic
      ** character, discard the initial "/" from the pathname.
      */
      if( zRelative.Length >= 3 && zRelative[0]=='/' && Char.IsLetter(zRelative[1]) && zRelative[2]==':' ){
        zRelative = zRelative.Substring(1);
      }

      /* It's odd to simulate an io-error here, but really this is just
      ** using the io-error infrastructure to test that SQLite handles this
      ** function failing. This function could fail if, for example, the
      ** current working directory has been unlinked.
      */
#if SQLITE_TEST
      if ( SimulateIOError() )
        return SQLITE_ERROR;
#endif
      UNUSED_PARAMETER( nFull );
      //convertUtf8Filename(zRelative));
      if ( isNT() )
      {
        //string zTemp;
        //nByte = GetFullPathNameW( zConverted, 0, 0, 0) + 3;
        //zTemp = malloc( nByte*sizeof(zTemp[0]) );
        //if( zTemp==0 ){
        //  free(zConverted);
        //  return SQLITE_NOMEM;
        //}
        //zTemp = GetFullPathNameW(zConverted, nByte, zTemp, 0);
        // will happen on exit; was   free(zConverted);
        try
        {
#if WINDOWS_PHONE || SQLITE_SILVERLIGHT  || SQLITE_WINRT
            zOut = zRelative;
#else
          if (Environment.OSVersion.Platform == PlatformID.Unix
            && zRelative.Length > 2 && zRelative[0] == '~' && (zRelative[1] == '/' || zRelative[1] == '\\'))
          {
            string home = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
            zOut = Path.GetFullPath(home + zRelative.Substring(1));
          }
          else
          {
            zOut = Path.GetFullPath( zRelative ); // was unicodeToUtf8(zTemp);
          }
#endif
        }
        catch ( Exception  e )
        {
          zOut = zRelative;
        }
        // will happen on exit; was   free(zTemp);
        /* isNT() is 1 if SQLITE_OS_WINCE==1, so this else is never executed.
        ** Since the ASCII version of these Windows API do not exist for WINCE,
        ** it's important to not reference them for WINCE builds.
        */
#if !SQLITE_OS_WINCE
      }
      else
      {
        Debugger.Break(); // -- Not Running under NT
        //string zTemp;
        //nByte = GetFullPathNameA(zConverted, 0, 0, 0) + 3;
        //zTemp = malloc( nByte*sizeof(zTemp[0]) );
        //if( zTemp==0 ){
        //  free(zConverted);
        //  return SQLITE_NOMEM;
        //}
        //GetFullPathNameA( zConverted, nByte, zTemp, 0);
        // free(zConverted);
        //zOut = sqlite3_win32_mbcs_to_utf8(zTemp);
        // free(zTemp);
#endif
      }
      if ( zOut != null )
      {
        // sqlite3_snprintf(pVfs.mxPathname, zFull, "%s", zOut);
        if ( zFull.Length > pVfs.mxPathname )
          zFull.Length = pVfs.mxPathname;
        zFull.Append( zOut );

        // will happen on exit; was   free(zOut);
        return SQLITE_OK;
      }
      else
      {
        return SQLITE_NOMEM;
      }
#endif
    }


    /*
    ** Get the sector size of the device used to store
    ** file.
    */
    static int getSectorSize(
    sqlite3_vfs pVfs,
    string zRelative     /* UTF-8 file name */
    )
    {
#if FALSE
int bytesPerSector = SQLITE_DEFAULT_SECTOR_SIZE;
/* GetDiskFreeSpace is not supported under WINCE */
#if SQLITE_OS_WINCE
UNUSED_PARAMETER(pVfs);
UNUSED_PARAMETER(zRelative);
#else
StringBuilder zFullpath = new StringBuilder( MAX_PATH + 1 );
int rc;
//bool dwRet = false;
//int dwDummy = 0;

/*
** We need to get the full path name of the file
** to get the drive letter to look up the sector
** size.
*/
SimulateIOErrorBenign(1);
rc = winFullPathname( pVfs, zRelative, MAX_PATH, zFullpath );
#if SQLITE_TEST
SimulateIOError( return SQLITE_ERROR )
#endif
if ( rc == SQLITE_OK )
{
StringBuilder zConverted = new StringBuilder( convertUtf8Filename( zFullpath.ToString() ) );
if ( zConverted.Length != 0 )
{
if ( isNT() )
{
/* trim path to just drive reference */
//for ( ; *p ; p++ )
//{
//  if ( *p == '\\' )
//  {
//    *p = '\0';
//    break;
//  }
//}
int i;
for ( i = 0 ; i < zConverted.Length && i < MAX_PATH ; i++ )
{
if ( zConverted[i] == '\\' )
{
i++;
break;
}
}
zConverted.Length = i;
//dwRet = GetDiskFreeSpace( zConverted,
//     ref dwDummy,
//     ref bytesPerSector,
//     ref dwDummy,
//     ref dwDummy );
//}else{
//  /* trim path to just drive reference */
//   char *p = (char )zConverted;
//  for ( ; *p ; p++ )
//  {
//    if ( *p == '\\' )
//    {
//      *p = '\0';
//      break;
//    }
//  }
//        dwRet = GetDiskFreeSpaceA((char)zConverted,
//                                  dwDummy,
//                                  ref bytesPerSector,
//                                  dwDummy,
//                                  dwDummy );
}
//free(zConverted);
}
//  if ( !dwRet )
//  {
//    bytesPerSector = SQLITE_DEFAULT_SECTOR_SIZE;
//  }
//}
//#endif
bytesPerSector = GetbytesPerSector( zConverted );
}
#endif
return bytesPerSector == 0 ? SQLITE_DEFAULT_SECTOR_SIZE : bytesPerSector;
#endif
      return SQLITE_DEFAULT_SECTOR_SIZE;
    }

#if !SQLITE_OMIT_LOAD_EXTENSION
    /*
** Interfaces for opening a shared library, finding entry points
** within the shared library, and closing the shared library.
*/
    /*
    ** Interfaces for opening a shared library, finding entry points
    ** within the shared library, and closing the shared library.
    */
    //static void winDlOpen(sqlite3_vfs pVfs, string zFilename){
    //  HANDLE h;
    //  void *zConverted = convertUtf8Filename(zFilename);
    //  UNUSED_PARAMETER(pVfs);
    //  if( zConverted==0 ){
    //    return 0;
    //  }
    //  if( isNT() ){
    //    h = LoadLibraryW((WCHAR)zConverted);
    /* isNT() is 1 if SQLITE_OS_WINCE==1, so this else is never executed.
    ** Since the ASCII version of these Windows API do not exist for WINCE,
    ** it's important to not reference them for WINCE builds.
    */
#if !SQLITE_OS_WINCE
    //  }else{
    //    h = LoadLibraryA((char)zConverted);
#endif
    //  }
    //  free(zConverted);
    //  return (void)h;
    //}
    //static void winDlError(sqlite3_vfs pVfs, int nBuf, string zBufOut){
    //  UNUSED_PARAMETER(pVfs);
    //  getLastErrorMsg(nBuf, zBufOut);
    //}
    //    static object winDlSym(sqlite3_vfs pVfs, HANDLE pHandle, String zSymbol){
    //  UNUSED_PARAMETER(pVfs);
    //#if SQLITE_OS_WINCE
    //      /* The GetProcAddressA() routine is only available on wince. */
    //      return GetProcAddressA((HANDLE)pHandle, zSymbol);
    //#else
    //     /* All other windows platforms expect GetProcAddress() to take
    //      ** an Ansi string regardless of the _UNICODE setting */
    //      return GetProcAddress((HANDLE)pHandle, zSymbol);
    //#endif
    //   }
    //    static void winDlClose( sqlite3_vfs pVfs, HANDLE pHandle )
    //   {
    //  UNUSED_PARAMETER(pVfs);
    //     FreeLibrary((HANDLE)pHandle);
    //   }
    //TODO -- Fix This
    static HANDLE winDlOpen( sqlite3_vfs vfs, string zFilename )
    {
      return new HANDLE();
    }
    static int winDlError( sqlite3_vfs vfs, int nByte, string zErrMsg )
    {
      return 0;
    }
    static HANDLE winDlSym( sqlite3_vfs vfs, HANDLE data, string zSymbol )
    {
      return new HANDLE();
    }
    static int winDlClose( sqlite3_vfs vfs, HANDLE data )
    {
      return 0;
    }
#else // * if SQLITE_OMIT_LOAD_EXTENSION is defined: */
static object winDlOpen(ref sqlite3_vfs vfs, string zFilename) { return null; }
static int winDlError(ref sqlite3_vfs vfs, int nByte, ref string zErrMsg) { return 0; }
static object winDlSym(ref sqlite3_vfs vfs, object data, string zSymbol) { return null; }
static int winDlClose(ref sqlite3_vfs vfs, object data) { return 0; }
#endif


    /*
** Write up to nBuf bytes of randomness into zBuf.
*/

    //[StructLayout( LayoutKind.Explicit, Size = 16, CharSet = CharSet.Ansi )]
    //public class _SYSTEMTIME
    //{
    //  [FieldOffset( 0 )]
    //  public u32 byte_0_3;
    //  [FieldOffset( 4 )]
    //  public u32 byte_4_7;
    //  [FieldOffset( 8 )]
    //  public u32 byte_8_11;
    //  [FieldOffset( 12 )]
    //  public u32 byte_12_15;
    //}
    //[DllImport( "Kernel32.dll" )]
    //private static extern bool QueryPerformanceCounter( out long lpPerformanceCount );

    static int winRandomness( sqlite3_vfs pVfs, int nBuf, byte[] zBuf )
    {
      int n = 0;
      UNUSED_PARAMETER( pVfs );
#if (SQLITE_TEST)
      n = nBuf;
      Array.Clear( zBuf, 0, n );// memset( zBuf, 0, nBuf );
#else
byte[] sBuf = BitConverter.GetBytes(System.DateTime.Now.Ticks);
zBuf[0] = sBuf[0];
zBuf[1] = sBuf[1];
zBuf[2] = sBuf[2];
zBuf[3] = sBuf[3];
;// memcpy(&zBuf[n], x, sizeof(x))
n += 16;// sizeof(x);
if ( sizeof( DWORD ) <= nBuf - n )
{
//DWORD pid = GetCurrentProcessId();
u32 processId;
#if !(SQLITE_SILVERLIGHT || SQLITE_WINRT)
processId = (u32)Process.GetCurrentProcess().Id; 
#else
processId = 28376023;
#endif
put32bits( zBuf, n, processId);//(memcpy(&zBuf[n], pid, sizeof(pid));
n += 4;// sizeof(pid);
}
if ( sizeof( DWORD ) <= nBuf - n )
{
//DWORD cnt = GetTickCount();
System.DateTime dt = new System.DateTime();
put32bits( zBuf, n, (u32)dt.Ticks );// memcpy(&zBuf[n], cnt, sizeof(cnt));
n += 4;// cnt.Length;
}
if ( sizeof( long ) <= nBuf - n )
{
long i;
i = System.DateTime.UtcNow.Millisecond;// QueryPerformanceCounter(out i);
put32bits( zBuf, n, (u32)( i & 0xFFFFFFFF ) );//memcpy(&zBuf[n], i, sizeof(i));
put32bits( zBuf, n, (u32)( i >> 32 ) );
n += sizeof( long );
}
#endif
      return n;
    }


    /*
    ** Sleep for a little while.  Return the amount of time slept.
    */
    static int winSleep( sqlite3_vfs pVfs, int microsec )
    {
#if SQLITE_WINRT
        System.Threading.Tasks.Task.Delay(((microsec + 999) / 1000)).Wait();

#else
      Thread.Sleep(((microsec + 999) / 1000));
#endif
      UNUSED_PARAMETER( pVfs );
      return ( ( microsec + 999 ) / 1000 ) * 1000;
    }

    /*
    ** The following variable, if set to a non-zero value, is interpreted as
    ** the number of seconds since 1970 and is used to set the result of
    ** sqlite3OsCurrentTime() during testing.
    */
#if SQLITE_TEST
#if !TCLSH
    static int sqlite3_current_time = 0;//  /* Fake system time in seconds since 1970. */
#else
    static tcl.lang.Var.SQLITE3_GETSET sqlite3_current_time = new tcl.lang.Var.SQLITE3_GETSET( "sqlite3_current_time" );
#endif
#endif

    /*
** Find the current time (in Universal Coordinated Time).  Write into *piNow
** the current time and date as a Julian Day number times 86_400_000.  In
** other words, write into *piNow the number of milliseconds since the Julian
** epoch of noon in Greenwich on November 24, 4714 B.C according to the
** proleptic Gregorian calendar.
**
** On success, return 0.  Return 1 if the time and date cannot be found.
*/
    static int winCurrentTimeInt64( sqlite3_vfs pVfs, ref sqlite3_int64 piNow )
    {
      /* FILETIME structure is a 64-bit value representing the number of
      100-nanosecond intervals since January 1, 1601 (= JD 2305813.5).
      */
      //var ft = new FILETIME();
#if SQLITE_WINRT
        const sqlite3_int64 winRtEpoc = 17214255 * (sqlite3_int64)8640000;
#else
        const sqlite3_int64 winFiletimeEpoch = 23058135 * (sqlite3_int64)8640000;
#endif
#if SQLITE_TEST
      const sqlite3_int64 unixEpoch = 24405875 * (sqlite3_int64)8640000;
#endif

      ///* 2^32 - to avoid use of LL and warnings in gcc */
      //const sqlite3_int64 max32BitValue =
      //(sqlite3_int64)2000000000 + (sqlite3_int64)2000000000 + (sqlite3_int64)294967296;

      //#if SQLITE_OS_WINCE
      //SYSTEMTIME time;
      //GetSystemTime(&time);
      ///* if SystemTimeToFileTime() fails, it returns zero. */
      //if (!SystemTimeToFileTime(&time,&ft)){
      //return 1;
      //}
      //#else
      //      GetSystemTimeAsFileTime( ref ft );
      //      ft = System.DateTime.UtcNow.ToFileTime();
      //#endif
      //sqlite3_int64 ft = System.DateTime.UtcNow.ToFileTime();
      //piNow = winFiletimeEpoch + ft;
      //((((sqlite3_int64)ft.dwHighDateTime)*max32BitValue) + 
      //   (sqlite3_int64)ft.dwLowDateTime)/(sqlite3_int64)10000;
#if SQLITE_WINRT
    piNow = winRtEpoc + System.DateTime.UtcNow.Ticks / (sqlite3_int64)10000;
#else
      piNow = winFiletimeEpoch + System.DateTime.UtcNow.ToFileTimeUtc() / (sqlite3_int64)10000;
#endif
#if SQLITE_TEST
#if !TCLSH
      if ( ( sqlite3_current_time) != 0 )
      {
        piNow = 1000 * (sqlite3_int64)sqlite3_current_time + unixEpoch;
      }
#else
      if ( ( sqlite3_current_time.iValue ) != 0 )
      {
        piNow = 1000 * (sqlite3_int64)sqlite3_current_time.iValue + unixEpoch;
      }
#endif
#endif
        UNUSED_PARAMETER( pVfs );
      return 0;
    }


    /*
    ** Find the current time (in Universal Coordinated Time).  Write the
    ** current time and date as a Julian Day number into *prNow and
    ** return 0.  Return 1 if the time and date cannot be found.
    */
    static int winCurrentTime( sqlite3_vfs pVfs, ref double prNow )
    {
      int rc;
      sqlite3_int64 i = 0;
      rc = winCurrentTimeInt64( pVfs, ref i );
      if ( 0 == rc )
      {
        prNow = i / 86400000.0;
      }
      return rc;
    }

    /*
    ** The idea is that this function works like a combination of
    ** GetLastError() and FormatMessage() on windows (or errno and
    ** strerror_r() on unix). After an error is returned by an OS
    ** function, SQLite calls this function with zBuf pointing to
    ** a buffer of nBuf bytes. The OS layer should populate the
    ** buffer with a nul-terminated UTF-8 encoded error message
    ** describing the last IO error to have occurred within the calling
    ** thread.
    **
    ** If the error message is too large for the supplied buffer,
    ** it should be truncated. The return value of xGetLastError
    ** is zero if the error message fits in the buffer, or non-zero
    ** otherwise (if the message was truncated). If non-zero is returned,
    ** then it is not necessary to include the nul-terminator character
    ** in the output buffer.
    **
    ** Not supplying an error message will have no adverse effect
    ** on SQLite. It is fine to have an implementation that never
    ** returns an error message:
    **
    **   int xGetLastError(sqlite3_vfs pVfs, int nBuf, string zBuf){
    **     Debug.Assert(zBuf[0]=='\0');
    **     return 0;
    **   }
    **
    ** However if an error message is supplied, it will be incorporated
    ** by sqlite into the error message available to the user using
    ** sqlite3_errmsg(), possibly making IO errors easier to debug.
    */
    static int winGetLastError( sqlite3_vfs pVfs, int nBuf, ref string zBuf )
    {
      UNUSED_PARAMETER( pVfs );
      return getLastErrorMsg( nBuf, ref zBuf );
    }

    static sqlite3_vfs winVfs = new sqlite3_vfs(
    3,                              /* iVersion */
    -1, //sqlite3_file.Length,      /* szOsFile */
    MAX_PATH,                       /* mxPathname */
    null,                           /* pNext */
    "win32",                        /* zName */
    0,                              /* pAppData */

    (dxOpen)winOpen,                /* xOpen */
    (dxDelete)winDelete,            /* xDelete */
    (dxAccess)winAccess,            /* xAccess */
    (dxFullPathname)winFullPathname,/* xFullPathname */
    (dxDlOpen)winDlOpen,            /* xDlOpen */
    (dxDlError)winDlError,          /* xDlError */
    (dxDlSym)winDlSym,              /* xDlSym */
    (dxDlClose)winDlClose,          /* xDlClose */
    (dxRandomness)winRandomness,    /* xRandomness */
    (dxSleep)winSleep,              /* xSleep */
    (dxCurrentTime)winCurrentTime,  /* xCurrentTime */
    (dxGetLastError)winGetLastError,/* xGetLastError */
    (dxCurrentTimeInt64)winCurrentTimeInt64, /* xCurrentTimeInt64 */
    null,                           /* xSetSystemCall */
    null,                           /* xGetSystemCall */
    null                            /* xNextSystemCall */
    );

    /*
    ** Initialize and deinitialize the operating system interface.
    */
    static int sqlite3_os_init()
    {
#if !SQLITE_OMIT_WAL
/* get memory map allocation granularity */
memset(&winSysInfo, 0, sizeof(SYSTEM_INFO));
GetSystemInfo(&winSysInfo);
Debug.Assert(winSysInfo.dwAllocationGranularity > 0);
#endif

      sqlite3_vfs_register( winVfs, 1 );
      return SQLITE_OK;
    }

    static int sqlite3_os_end()
    {
      return SQLITE_OK;
    }

#endif // * SQLITE_OS_WIN */
    //
    //          Windows DLL definitions
    //

    const int NO_ERROR = 0;
    /// <summary>
    /// Basic locking strategy for Console/Winform applications
    /// </summary>
    private class LockingStrategy
    {
#if !(SQLITE_SILVERLIGHT || WINDOWS_MOBILE || SQLITE_WINRT)
      [DllImport( "kernel32.dll" )]
      static extern bool LockFileEx( IntPtr hFile, uint dwFlags, uint dwReserved,
      uint nNumberOfBytesToLockLow, uint nNumberOfBytesToLockHigh,
      [In] ref System.Threading.NativeOverlapped lpOverlapped );

      const int LOCKFILE_FAIL_IMMEDIATELY = 1;
#endif

      private int LockUnix( sqlite3_file pFile, long offset, long length, bool locking, bool shared = false)
      {
        int fd = pFile.fs.Handle.ToInt32();
        Mono.Unix.Native.Flock flock = new() {
            l_whence = Mono.Unix.Native.SeekFlags.SEEK_SET,
            l_start = offset,
            l_len = length,
            l_type = !locking ? Mono.Unix.Native.LockType.F_UNLCK
                     : shared ? Mono.Unix.Native.LockType.F_RDLCK
                     : Mono.Unix.Native.LockType.F_WRLCK,
        };

        int result = Mono.Unix.Native.Syscall.fcntl(fd, Mono.Unix.Native.FcntlCommand.F_SETLK, ref flock);
        return result != -1 ? 1 : 0;
      }

      public virtual void LockFile( sqlite3_file pFile, long offset, long length )
      {
        if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX) || RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
        {
          LockUnix( pFile, offset, length, locking: true );
        }
        else
        {
          pFile.fs.Lock( offset, length );
        }
      }

      public virtual int SharedLockFile( sqlite3_file pFile, long offset, long length )
      {
#if !(SQLITE_SILVERLIGHT || WINDOWS_MOBILE || SQLITE_WINRT)
        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
        {
          Debug.Assert( length == SHARED_SIZE );
          Debug.Assert( offset == SHARED_FIRST );
          NativeOverlapped ovlp = new NativeOverlapped();
          ovlp.OffsetLow = (int)offset;
          ovlp.OffsetHigh = 0;
          ovlp.EventHandle = IntPtr.Zero;

          return LockFileEx( pFile.fs.Handle, LOCKFILE_FAIL_IMMEDIATELY, 0, (uint)length, 0, ref ovlp ) ? 1 : 0;
        }
        else
        {
          return LockUnix( pFile, offset, length, locking: true, shared: true );
        }
#else
            return 1;
#endif
      }

      public virtual void UnlockFile( sqlite3_file pFile, long offset, long length )
      {
#if !(SQLITE_SILVERLIGHT || WINDOWS_MOBILE || SQLITE_WINRT)
        if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX) || RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
        {
          LockUnix( pFile, offset, length, locking: false );
        }
        else
        {
          pFile.fs.Unlock( offset, length );
        }
#endif
      }
    }

    /// <summary>
    /// Locking strategy for Medium Trust. It uses the same trick used in the native code for WIN_CE
    /// which doesn't support LockFileEx as well.
    /// </summary>
    private class MediumTrustLockingStrategy : LockingStrategy
    {
      public override int SharedLockFile( sqlite3_file pFile, long offset, long length )
        {
#if !(SQLITE_SILVERLIGHT || WINDOWS_MOBILE || SQLITE_WINRT)
        Debug.Assert( length == SHARED_SIZE );
        Debug.Assert( offset == SHARED_FIRST );
        try
        {
          if (!RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
          {
            pFile.fs.Lock( offset + pFile.sharedLockByte, 1 );
          }
        }
        catch ( IOException )
        {
          return 0;
        }
#endif
            return 1;
      }
    }
  }
  internal static class HelperMethods
  {
      public static bool IsRunningMediumTrust() {
          // placeholder method
          // this is where it needs to check if it's running in an ASP.Net MediumTrust or lower environment
          // in order to pick the appropriate locking strategy
          return false;
      }

#if SQLITE_WINRT
    public static bool FileExists(string path)
    {
        bool exists = true;
        try
        {
            Task<StorageFile> fileTask = StorageFile.GetFileFromPathAsync(path).AsTask<StorageFile>();
            fileTask.Wait();
        }
        catch (Exception e)
        {
            AggregateException ae = e as AggregateException;
            if (ae != null && ae.InnerException is FileNotFoundException)
                exists = false;
        }
        return exists;
    }
#endif

    public static int GetLastError()
    {
      return Marshal.GetLastWin32Error();
    }
  }
}