1 files changed, 36 insertions, 14 deletions
diff --git a/std/async/pool.ts b/std/async/pool.ts
index 8aeb2671d..0b87f24ac 100644
--- a/std/async/pool.ts
+++ b/std/async/pool.ts
@@ -4,8 +4,13 @@
  * pooledMap transforms values from an (async) iterable into another async
  * iterable. The transforms are done concurrently, with a max concurrency
  * defined by the poolLimit.
- * 
- * @param poolLimit The maximum count of items being processed concurrently. 
+ *
+ * If an error is thrown from `iterableFn`, no new transformations will begin.
+ * All currently executing transformations are allowed to finish and still
+ * yielded on success. After that, the rejections among them are gathered and
+ * thrown by the iterator in an `AggregateError`.
+ *
+ * @param poolLimit The maximum count of items being processed concurrently.
  * @param array The input array for mapping.
  * @param iteratorFn The function to call for every item of the array.
  */
@@ -27,20 +32,37 @@ export function pooledMap<T, R>(
   (async (): Promise<void> => {
     const writer = res.writable.getWriter();
     const executing: Array<Promise<unknown>> = [];
-    for await (const item of array) {
-      const p = Promise.resolve().then(() => iteratorFn(item));
-      writer.write(p);
-      const e: Promise<unknown> = p.then(() =>
-        executing.splice(executing.indexOf(e), 1)
-      );
-      executing.push(e);
-      if (executing.length >= poolLimit) {
-        await Promise.race(executing);
+    try {
+      for await (const item of array) {
+        const p = Promise.resolve().then(() => iteratorFn(item));
+        // Only write on success. If we `writer.write()` a rejected promise,
+        // that will end the iteration. We don't want that yet. Instead let it
+        // fail the race, taking us to the catch block where all currently
+        // executing jobs are allowed to finish and all rejections among them
+        // can be reported together.
+        p.then((v) => writer.write(Promise.resolve(v))).catch(() => {});
+        const e: Promise<unknown> = p.then(() =>
+          executing.splice(executing.indexOf(e), 1)
+        );
+        executing.push(e);
+        if (executing.length >= poolLimit) {
+          await Promise.race(executing);
+        }
       }
+      // Wait until all ongoing events have processed, then close the writer.
+      await Promise.all(executing);
+      writer.close();
+    } catch {
+      const errors = [];
+      for (const result of await Promise.allSettled(executing)) {
+        if (result.status == "rejected") {
+          errors.push(result.reason);
+        }
+      }
+      writer.write(Promise.reject(
+        new AggregateError(errors, "Threw while mapping."),
+      )).catch(() => {});
     }
-    // Wait until all ongoing events have processed, then close the writer.
-    await Promise.all(executing);
-    writer.close();
   })();
   return res.readable[Symbol.asyncIterator]();
 }