fix: prevent worker process hanging with proper timer cleanup (#13)

fix: prevent worker process hanging with proper timer cleanup
    
Fixes 'A worker process has failed to exit gracefully' error by ensuring
all setTimeout timers are properly cleaned up.
    
## Root Cause:
    - waitBeforeContinue creates multiple polling timers via setTimeout
    - Promise.race resolves when any condition is met
    - Remaining timers from unresolved promises kept running
    - Jest worker processes couldn't exit due to active handles
    
## Solution:
    - Track all setTimeout timers in arrays
    - Clear all timers after Promise.race resolves
    - Add proper cleanup in both implementation and tests
    - Prevent resource leaks and hanging processes
    
## Changes:
    - waitBeforeContinue: Track and cleanup timers after Promise.race
    - Tests: Track test timers and clear in afterEach hooks
    - Eliminates worker process hanging warnings
    - Ensures proper resource management in production

Co-authored-by: Pooya Paridel <parpooya@amazon.com>

Author: ParidelPooya

packages/lambda-durable-functions-sdk-js/src/utils/wait-before-continue/wait-before-continue.test.ts

@@ -5,12 +5,20 @@ import { OperationStatus, Operation } from '@amzn/dex-internal-sdk';
 describe('waitBeforeContinue', () => {
   let mockContext: jest.Mocked<ExecutionContext>;
   let mockHasRunningOperations: jest.Mock;
+  let timers: NodeJS.Timeout[] = [];
 
   beforeEach(() => {
     mockContext = {
       getStepData: jest.fn(),
     } as any;
     mockHasRunningOperations = jest.fn();
+    timers = [];
+  });
+
+  afterEach(() => {
+    // Clean up any remaining timers
+    timers.forEach(timer => clearTimeout(timer));
+    timers = [];
   });
 
   test('should resolve when operations complete', async () => {
@@ -28,9 +36,10 @@ describe('waitBeforeContinue', () => {
     });
 
     // Complete operations after 50ms
-    setTimeout(() => {
+    const timer = setTimeout(() => {
       operationsRunning = false;
     }, 50);
+    timers.push(timer);
 
     const result = await resultPromise;
     expect(result.reason).toBe('operations');
@@ -68,9 +77,10 @@ describe('waitBeforeContinue', () => {
     });
 
     // Change status after 50ms
-    setTimeout(() => {
+    const timer = setTimeout(() => {
       stepStatus = OperationStatus.SUCCEEDED;
     }, 50);
+    timers.push(timer);
 
     const result = await resultPromise;
     expect(result.reason).toBe('status');

packages/lambda-durable-functions-sdk-js/src/utils/wait-before-continue/wait-before-continue.ts

@@ -54,13 +54,20 @@ export async function waitBeforeContinue(
   } = options;
 
   const promises: Promise<WaitBeforeContinueResult>[] = [];
+  const timers: NodeJS.Timeout[] = [];
+
+  // Cleanup function to clear all timers
+  const cleanup = () => {
+    timers.forEach(timer => clearTimeout(timer));
+  };
 
   // Timer promise - resolves when scheduled time is reached
   if (checkTimer && scheduledTimestamp) {
     const timerPromise = new Promise<WaitBeforeContinueResult>(resolve => {
       const timeLeft = Number(scheduledTimestamp) - Date.now();
       if (timeLeft > 0) {
-        setTimeout(() => resolve({ reason: 'timer', timerExpired: true }), timeLeft);
+        const timer = setTimeout(() => resolve({ reason: 'timer', timerExpired: true }), timeLeft);
+        timers.push(timer);
       } else {
         resolve({ reason: 'timer', timerExpired: true });
       }
@@ -75,7 +82,8 @@ export async function waitBeforeContinue(
         if (!hasRunningOperations()) {
           resolve({ reason: 'operations' });
         } else {
-          setTimeout(checkOperations, pollingInterval);
+          const timer = setTimeout(checkOperations, pollingInterval);
+          timers.push(timer);
         }
       };
       checkOperations();
@@ -92,7 +100,8 @@ export async function waitBeforeContinue(
         if (originalStatus !== currentStatus) {
           resolve({ reason: 'status' });
         } else {
-          setTimeout(checkStepStatus, pollingInterval);
+          const timer = setTimeout(checkStepStatus, pollingInterval);
+          timers.push(timer);
         }
       };
       checkStepStatus();
@@ -105,8 +114,9 @@ export async function waitBeforeContinue(
     return { reason: 'timeout' };
   }
 
-  // Wait for any condition to be met
+  // Wait for any condition to be met, then cleanup timers
   const result = await Promise.race(promises);
+  cleanup();
 
   // If timer expired, force checkpoint to get fresh data from API
   if (result.reason === 'timer' && result.timerExpired && checkpoint) {