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// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
import { Deferred, deferred } from "./deferred.ts";
interface TaggedYieldedValue<T> {
iterator: AsyncIterableIterator<T>;
value: T;
}
/** The MuxAsyncIterator class multiplexes multiple async iterators into a
* single stream. It currently makes an assumption:
* - The final result (the value returned and not yielded from the iterator)
* does not matter; if there is any, it is discarded.
*/
export class MuxAsyncIterator<T> implements AsyncIterable<T> {
private iteratorCount = 0;
private yields: Array<TaggedYieldedValue<T>> = [];
// eslint-disable-next-line @typescript-eslint/no-explicit-any
private throws: any[] = [];
private signal: Deferred<void> = deferred();
add(iterator: AsyncIterableIterator<T>): void {
++this.iteratorCount;
this.callIteratorNext(iterator);
}
private async callIteratorNext(
iterator: AsyncIterableIterator<T>
): Promise<void> {
try {
const { value, done } = await iterator.next();
if (done) {
--this.iteratorCount;
} else {
this.yields.push({ iterator, value });
}
} catch (e) {
this.throws.push(e);
}
this.signal.resolve();
}
async *iterate(): AsyncIterableIterator<T> {
while (this.iteratorCount > 0) {
// Sleep until any of the wrapped iterators yields.
await this.signal;
// Note that while we're looping over `yields`, new items may be added.
for (let i = 0; i < this.yields.length; i++) {
const { iterator, value } = this.yields[i];
yield value;
this.callIteratorNext(iterator);
}
if (this.throws.length) {
for (const e of this.throws) {
throw e;
}
this.throws.length = 0;
}
// Clear the `yields` list and reset the `signal` promise.
this.yields.length = 0;
this.signal = deferred();
}
}
[Symbol.asyncIterator](): AsyncIterableIterator<T> {
return this.iterate();
}
}
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