Make queue resilient to sync errors

Author: Michelle Tilley

lib/async-queue.js

@@ -8,8 +8,13 @@ class Task {
     });
   }
 
-  execute() {
-    return this.fn.call(undefined).then(this.resolve, this.reject);
+  async execute() {
+    try {
+      const value = await this.fn.call(undefined);
+      this.resolve(value);
+    } catch (err) {
+      this.reject(err);
+    }
   }
 
   runsInParallel() {
@@ -55,14 +60,9 @@ export default class AsyncQueue {
       this.nonParallelizableOperation = true;
     }
 
-    try {
-      await task.execute();
-    } catch (err) {
-      // nothing
-    } finally {
-      this.threadsInUse--;
-      this.nonParallelizableOperation = false;
-      this.processQueue();
-    }
+    await task.execute();
+    this.threadsInUse--;
+    this.nonParallelizableOperation = false;
+    this.processQueue();
   }
 }

test/async-queue.test.js

@@ -128,4 +128,21 @@ describe('AsyncQueue', function() {
     await assert.async.isTrue(tasks[4].started); // both can start since they are parallelizable
     assert.isTrue(tasks[5].started);
   });
+
+  it('continues to work when tasks throw synchronous errors', async function() {
+    const queue = new AsyncQueue({parallelism: 1});
+
+    const p1 = queue.push(() => {
+      throw new Error('error thrown from task 1');
+    });
+    const p2 = queue.push(() => {
+      return new Promise(res => res(2));
+    });
+
+    try {
+      await p1;
+      throw new Error('expected p1 to be rejectd');
+    } catch (err) {}
+    assert.equal(await p2, 2);
+  });
 });