1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
|
// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
/**
* pooledMap transforms values from an (async) iterable into another async
* iterable. The transforms are done concurrently, with a max concurrency
* defined by the poolLimit.
*
* 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.
*/
export function pooledMap<T, R>(
poolLimit: number,
array: Iterable<T> | AsyncIterable<T>,
iteratorFn: (data: T) => Promise<R>,
): AsyncIterableIterator<R> {
// Create the async iterable that is returned from this function.
const res = new TransformStream<Promise<R>, R>({
async transform(
p: Promise<R>,
controller: TransformStreamDefaultController<R>,
): Promise<void> {
controller.enqueue(await p);
},
});
// Start processing items from the iterator
(async (): Promise<void> => {
const writer = res.writable.getWriter();
const executing: Array<Promise<unknown>> = [];
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(() => {});
}
})();
return res.readable[Symbol.asyncIterator]();
}
|
