chore: prevent spawning concurrent subprocesses

- Update the cache file’s `mtime` before spawning the subprocess.
- Add `isChecking` flag to prevent concurrent checks in the same process, including while testing.

Author: mathiasbynens

src/utils/check-for-updates.ts

@@ -16,10 +16,18 @@ import {VERSION} from '../version.js';
  * Notifies the user if an update is available.
  * @param message The message to display in the update notification.
  */
+let isChecking = false;
+
+/** @internal Reset flag for tests only. */
+export function resetUpdateCheckFlagForTesting() {
+  isChecking = false;
+}
+
 export async function checkForUpdates(message: string) {
-  if (process.env['CHROME_DEVTOOLS_MCP_NO_UPDATE_CHECKS']) {
+  if (isChecking || process.env['CHROME_DEVTOOLS_MCP_NO_UPDATE_CHECKS']) {
     return;
   }
+  isChecking = true;
 
   const cachePath = path.join(
     os.homedir(),
@@ -49,6 +57,20 @@ export async function checkForUpdates(message: string) {
     return;
   }
 
+  // Update mtime immediately to prevent multiple subprocesses.
+  try {
+    const parentDir = path.dirname(cachePath);
+    await fs.mkdir(parentDir, {recursive: true});
+    const nowTime = new Date();
+    if (stats) {
+      await fs.utimes(cachePath, nowTime, nowTime);
+    } else {
+      await fs.writeFile(cachePath, JSON.stringify({version: VERSION}));
+    }
+  } catch {
+    // Ignore errors.
+  }
+
   // In a separate process, check the latest available version number
   // and update the local snapshot accordingly.
   const scriptPath = path.join(

tests/check-for-updates.test.ts

@@ -9,16 +9,26 @@ import child_process from 'node:child_process';
 import type {Stats} from 'node:fs';
 import fs from 'node:fs/promises';
 import os from 'node:os';
-import {afterEach, describe, it} from 'node:test';
+import {afterEach, beforeEach, describe, it} from 'node:test';
 
 import sinon from 'sinon';
 
-import {checkForUpdates} from '../src/utils/check-for-updates.js';
+import {
+  checkForUpdates,
+  resetUpdateCheckFlagForTesting,
+} from '../src/utils/check-for-updates.js';
 import {VERSION} from '../src/version.js';
 
 describe('checkForUpdates', () => {
+  beforeEach(() => {
+    sinon.stub(fs, 'mkdir').resolves();
+    sinon.stub(fs, 'utimes').resolves();
+    sinon.stub(fs, 'writeFile').resolves();
+  });
+
   afterEach(() => {
     sinon.restore();
+    resetUpdateCheckFlagForTesting();
   });
 
   it('does nothing if CHROME_DEVTOOLS_MCP_NO_UPDATE_CHECKS is set', async () => {