Prevent skip removal logic from being run twice

Author: huntharo

index.js

@@ -21,42 +21,43 @@ export default async function pMap(
 		const errors = [];
 		const skippedIndexes = [];
 		let isRejected = false;
+		let isRejectedOrResolved = false;
 		let isIterableDone = false;
 		let resolvingCount = 0;
 		let currentIndex = 0;
-		let asyncIterator = false;
-		let iterator;
-
-		if (iterable[Symbol.iterator] === undefined) {
-			// We've got an async iterable
-			iterator = iterable[Symbol.asyncIterator]();
-			asyncIterator = true;
-		} else {
-			iterator = iterable[Symbol.iterator]();
-		}
+		const iterator = iterable[Symbol.iterator] === undefined ? iterable[Symbol.asyncIterator]() : iterable[Symbol.iterator]();
 
 		const reject = reason => {
 			isRejected = true;
+			isRejectedOrResolved = true;
 			reject_(reason);
 		};
 
 		const next = async () => {
-			if (isRejected) {
+			if (isRejectedOrResolved) {
 				return;
 			}
 
-			const nextItem = asyncIterator ? await iterator.next() : iterator.next();
+			const nextItem = await iterator.next();
 
 			const index = currentIndex;
 			currentIndex++;
 
+			// Note: iterator.next() can be called many times in parallel.
+			// This can cause multiple calls to this next() function to
+			// receive a `nextItem` with `done === true`.
+			// The shutdown logic that rejects/resolves must be protected
+			// so it runs only one time as the `skippedIndex` logic is
+			// non-idempotent.
 			if (nextItem.done) {
 				isIterableDone = true;
 
-				if (resolvingCount === 0) {
+				if (resolvingCount === 0 && !isRejectedOrResolved) {
 					if (!stopOnError && errors.length > 0) {
 						reject(new AggregateError(errors));
 					} else {
+						isRejectedOrResolved = true;
+
 						for (const skippedIndex of skippedIndexes) {
 							result.splice(skippedIndex, 1);
 						}
@@ -75,7 +76,7 @@ export default async function pMap(
 				try {
 					const element = await nextItem.value;
 
-					if (isRejected) {
+					if (isRejectedOrResolved) {
 						return;
 					}
 

test.js

@@ -157,7 +157,7 @@ test('pMapSkip', async t => {
 	], async value => value), [1, 2]);
 });
 
-test('do not run mapping after stop-on-error happened', async t => {
+test('all mappers should run when concurrency is infinite, even after stop-on-error happened', async t => {
 	const input = [1, async () => delay(300, {value: 2}), 3];
 	const mappedValues = [];
 	await t.throwsAsync(
@@ -271,7 +271,7 @@ test('asyncIterator - pMapSkip', async t => {
 	]), async value => value), [1, 2]);
 });
 
-test('asyncIterator - do not run mapping after stop-on-error happened', async t => {
+test('asyncIterator - all mappers should run when concurrency is infinite, even after stop-on-error happened', async t => {
 	const input = [1, async () => delay(300, {value: 2}), 3];
 	const mappedValues = [];
 	await t.throwsAsync(
@@ -283,13 +283,13 @@ test('asyncIterator - do not run mapping after stop-on-error happened', async t
 			mappedValues.push(value);
 			if (value === 1) {
 				await delay(100);
-				throw new Error('Oops!');
+				throw new Error(`Oops! ${value}`);
 			}
-		},
-		{concurrency: 1})
+		}),
+		{message: 'Oops! 1'}
 	);
 	await delay(500);
-	t.deepEqual(mappedValues, [1]);
+	t.deepEqual(mappedValues, [1, 3, 2]);
 });
 
 test('catches exception from source iterator - 1st item', async t => {
@@ -349,3 +349,22 @@ test('catches exception from source iterator - 2nd item after 1st item mapper th
 	t.is(input.index, 2);
 	t.deepEqual(mappedValues, [0]);
 });
+
+test('asyncIterator - get the correct exception after stop-on-error', async t => {
+	const input = [1, async () => delay(200, {value: 2}), async () => delay(300, {value: 3})];
+	const mappedValues = [];
+
+	const task = pMap(new AsyncTestData(input), async value => {
+		if (typeof value === 'function') {
+			value = await value();
+		}
+
+		mappedValues.push(value);
+		// Throw for each item - all should fail and we should get only the first
+		await delay(100);
+		throw new Error(`Oops! ${value}`);
+	});
+	await delay(500);
+	await t.throwsAsync(task, {message: 'Oops! 1'});
+	t.deepEqual(mappedValues, [1, 2, 3]);
+});