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fix(std/async): make pooledMap() errors catchable (#9217)

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Nayeem Rahman 2021-01-22 11:45:29 +00:00 • committed by GitHub
parent 1a9209d1e3
commit 1518fabfbb
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2 changed files with 62 additions and 16 deletions
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50
std/async/pool.ts
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@ -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]();
}