From 01a03f2961f86cd08c6c90335101b0d10d141cad Mon Sep 17 00:00:00 2001
From: Oliver Eyton-Williams <ojeytonwilliams@gmail.com>
Date: Sat, 8 Jan 2022 07:12:16 +0100
Subject: [PATCH] fix: prevent timeout errors (#44714)

---
 .../Challenges/utils/worker-executor.js       | 79 +++++++++----------
 .../Challenges/utils/worker-executor.test.js  |  4 +-
 2 files changed, 41 insertions(+), 42 deletions(-)

diff --git a/client/src/templates/Challenges/utils/worker-executor.js b/client/src/templates/Challenges/utils/worker-executor.js
index 1c55302094..797a0e55cf 100644
--- a/client/src/templates/Challenges/utils/worker-executor.js
+++ b/client/src/templates/Challenges/utils/worker-executor.js
@@ -1,65 +1,59 @@
 class WorkerExecutor {
   constructor(
     workerName,
-    { location = '/js/', concurrency = 2, terminateWorker = false } = {}
+    { location = '/js/', maxWorkers = 2, terminateWorker = false } = {}
   ) {
-    this._workerName = workerName;
-    this._workers = [];
-    this._queue = [];
-    this._running = 0;
-    this._concurrency = concurrency;
+    this._workerPool = [];
+    this._taskQueue = [];
+    this._workersInUse = 0;
+    this._maxWorkers = maxWorkers;
     this._terminateWorker = terminateWorker;
-    this._location = location;
+    this._scriptURL = `${location}${workerName}.js`;
 
     this._getWorker = this._getWorker.bind(this);
   }
 
   async _getWorker() {
-    let worker;
-    if (this._workers.length) {
-      worker = this._workers.shift();
-    } else {
-      worker = await new Promise((resolve, reject) => {
-        const worker = new Worker(`${this._location}${this._workerName}.js`);
-        worker.onmessage = e => {
-          if (e.data && e.data.type && e.data.type === 'contentLoaded') {
-            resolve(worker);
-          }
-        };
-        worker.onerror = err => reject(err);
-      });
-    }
-    return worker;
+    return this._workerPool.length
+      ? this._workerPool.shift()
+      : this._createWorker();
   }
 
-  _pushTask(task) {
-    this._queue.push(task);
-    this._next();
+  _createWorker() {
+    return new Promise((resolve, reject) => {
+      const newWorker = new Worker(this._scriptURL);
+      newWorker.onmessage = e => {
+        if (e.data?.type === 'contentLoaded') {
+          resolve(newWorker);
+        }
+      };
+      newWorker.onerror = err => reject(err);
+    });
   }
 
   _handleTaskEnd(task) {
     return () => {
-      this._running--;
-      if (task._worker) {
-        const worker = task._worker;
+      this._workersInUse--;
+      const worker = task._worker;
+      if (worker) {
         if (this._terminateWorker) {
           worker.terminate();
         } else {
           worker.onmessage = null;
           worker.onerror = null;
-          this._workers.push(worker);
+          this._workerPool.push(worker);
         }
       }
-      this._next();
+      this._processQueue();
     };
   }
 
-  _next() {
-    while (this._running < this._concurrency && this._queue.length) {
-      const task = this._queue.shift();
+  _processQueue() {
+    while (this._workersInUse < this._maxWorkers && this._taskQueue.length) {
+      const task = this._taskQueue.shift();
       const handleTaskEnd = this._handleTaskEnd(task);
       task._execute(this._getWorker).done.then(handleTaskEnd, handleTaskEnd);
-      this._running++;
+      this._workersInUse++;
     }
   }
 
@@ -76,12 +70,15 @@ class WorkerExecutor {
           }, timeout);
 
           worker.onmessage = e => {
-            if (e.data && e.data.type) {
-              this.emit(e.data.type, e.data.data);
-              return;
-            }
             clearTimeout(timeoutId);
-            this.emit('done', e.data);
+            // data.type is undefined when the message has been processed
+            // successfully and defined when something else has happened (e.g.
+            // an error occurred)
+            if (e.data?.type) {
+              this.emit(e.data.type, e.data.data);
+            } else {
+              this.emit('done', e.data);
+            }
           };
 
           worker.onerror = e => {
@@ -102,11 +99,13 @@ class WorkerExecutor {
         .once('error', err => reject(err.message));
     });
 
-    this._pushTask(task);
+    this._taskQueue.push(task);
+    this._processQueue();
     return task;
   }
 }
 
+// Error and completion handling
 const eventify = self => {
   self._events = {};
 
diff --git a/client/src/templates/Challenges/utils/worker-executor.test.js b/client/src/templates/Challenges/utils/worker-executor.test.js
index c52daef6a6..c75fedeb8f 100644
--- a/client/src/templates/Challenges/utils/worker-executor.test.js
+++ b/client/src/templates/Challenges/utils/worker-executor.test.js
@@ -124,7 +124,7 @@ it('Worker executor should successfully execute 3 tasks, use 3 workers and termi
 // eslint-disable-next-line max-len
 it('Worker executor should successfully execute 3 tasks in parallel and use 3 workers', async () => {
   mockWorker();
-  const testWorker = createWorker('test', { concurrency: 3 });
+  const testWorker = createWorker('test', { maxWorkers: 3 });
 
   const task1 = testWorker.execute('test1');
   const task2 = testWorker.execute('test2');
@@ -139,7 +139,7 @@ it('Worker executor should successfully execute 3 tasks in parallel and use 3 wo
 // eslint-disable-next-line max-len
 it('Worker executor should successfully execute 3 tasks and use 1 worker', async () => {
   mockWorker();
-  const testWorker = createWorker('test', { concurrency: 1 });
+  const testWorker = createWorker('test', { maxWorkers: 1 });
 
   const task1 = testWorker.execute('test1');
   const task2 = testWorker.execute('test2');