Make locks releasable more than once

Author: rix0rrr

packages/@aws-cdk/tmp-toolkit-helpers/src/api/rwlock.ts

@@ -39,9 +39,14 @@ export class RWLock {
 
     await writeFileAtomic(this.writerFile, this.pidString);
 
+    let released = false;
     return {
       release: async () => {
-        await deleteFile(this.writerFile);
+        // Releasing needs a flag, otherwise we might delete a file that some other lock has created in the mean time.
+        if (!released) {
+          await deleteFile(this.writerFile);
+          released = true;
+        }
       },
       convertToReaderLock: async () => {
         // Acquire the read lock before releasing the write lock. Slightly less
@@ -80,9 +85,15 @@ export class RWLock {
   private async doAcquireRead(): Promise<IReadLock> {
     const readerFile = this.readerFile();
     await writeFileAtomic(readerFile, this.pidString);
+
+    let released = false;
     return {
       release: async () => {
-        await deleteFile(readerFile);
+        // Releasing needs a flag, otherwise we might delete a file that some other lock has created in the mean time.
+        if (!released) {
+          await deleteFile(readerFile);
+          released = true;
+        }
       },
     };
   }
@@ -152,6 +163,9 @@ export class RWLock {
  * An acquired lock
  */
 export interface IReadLock {
+  /**
+   * Release the lock. Can be called more than once.
+   */
   release(): Promise<void>;
 }
 

packages/aws-cdk/test/api/rwlock.test.ts

@@ -1,4 +1,5 @@
 /* eslint-disable import/order */
+import { promises as fs } from 'node:fs';
 import * as os from 'os';
 import * as path from 'path';
 import { RWLock } from '../../lib/api/rwlock';
@@ -51,3 +52,33 @@ test('can convert writer to reader lock', async () => {
     await r.release();
   }
 });
+
+test('can release writer lock more than once, second invocation does nothing', async () => {
+  const unlink = jest.spyOn(fs, 'unlink');
+
+  // GIVEN
+  const lock = new RWLock(testDir());
+  const r = await lock.acquireWrite();
+
+  // WHEN
+  await r.release();
+  expect(unlink).toHaveBeenCalledTimes(1);
+
+  await r.release();
+  expect(unlink).toHaveBeenCalledTimes(1);
+});
+
+test('can release reader lock more than once, second invocation does nothing', async () => {
+  const unlink = jest.spyOn(fs, 'unlink');
+
+  // GIVEN
+  const lock = new RWLock(testDir());
+  const r = await lock.acquireRead();
+
+  // WHEN
+  await r.release();
+  expect(unlink).toHaveBeenCalledTimes(1);
+
+  await r.release();
+  expect(unlink).toHaveBeenCalledTimes(1);
+});