Merge pull request #52 from chang-chao/master

Initializes Reservoir reset setting  eagerly.

Author: chrisradek

aws-xray-recorder-sdk-core/src/main/java/com/amazonaws/xray/strategy/sampling/reservoir/Reservoir.java

@@ -11,7 +11,7 @@ public class Reservoir {
     private final int tracesPerSecond;
     private final MaxFunction maxFunction;
     private final AtomicInteger usage = new AtomicInteger(0);
-    private final AtomicLong nextReset = new AtomicLong(0);
+    private final AtomicLong nextReset;
 
     public Reservoir() {
         this(0);
@@ -21,6 +21,9 @@ public Reservoir(int tracesPerSecond) {
         this.tracesPerSecond = tracesPerSecond;
         this.maxFunction =
             tracesPerSecond < 10 ? new LessThan10(tracesPerSecond) : new AtLeast10(tracesPerSecond);
+
+        long now = System.nanoTime();
+        this.nextReset = new AtomicLong(now + NANOS_PER_SECOND);
     }
 
     public boolean take() {

aws-xray-recorder-sdk-core/src/test/java/com/amazonaws/xray/strategy/sampling/reservoir/ReservoirTest.java

@@ -36,6 +36,19 @@ public class ReservoirTest {
         assertFalse(reservoir.take());
     }
 
+    @Test public void samplesFairNegativeNanoTime() {
+        mockStatic(System.class);
+        when(System.nanoTime()).thenReturn(-2 * NANOS_PER_SECOND);
+        Reservoir reservoir = new Reservoir(10);
+
+        when(System.nanoTime()).thenReturn(-2 * NANOS_PER_SECOND + 1);
+        assertTrue(reservoir.take());
+        when(System.nanoTime()).thenReturn(-2 * NANOS_PER_SECOND + 2);
+        assertTrue(reservoir.take());
+        when(System.nanoTime()).thenReturn(-2 * NANOS_PER_SECOND + 2);
+        assertFalse(reservoir.take());
+    }
+
     @Test public void resetsAfterASecond() {
         mockStatic(System.class);