@johngw/stream
Version:
Reactive programming tools using the WHATWG Streams API.
51 lines • 1.62 kB
JavaScript
import { without } from '@johngw/stream-common/Array';
import { all } from '@johngw/stream-common/Async';
import { immediatelyClosingReadableStream, } from '@johngw/stream-common/Stream';
import { IteratorSource } from './fromCollection.js';
import { SourceComposite } from './SourceComposite.js';
/**
* Given an ordered list of streams, queue their items from one stream at a time.
*
* @group Sources
* @see {@link merge:function}
* @example
* ```
* roundRobin([
* --1------2------3------4-------
* ----one-two--three-------------
* ])
*
* --1-one--2-two--3-three-4------
* ```
*/
export function roundRobin(streams, queuingStrategy) {
let readers = streams.map((stream) => stream.getReader());
return !streams.length
? immediatelyClosingReadableStream()
: new ReadableStream(new SourceComposite([
new IteratorSource(generateReadResults()),
{
async cancel(reason) {
await all(readers, (reader) => reader.cancel(reason));
},
},
]), queuingStrategy);
async function* generateReadResults() {
let index = 0;
while (readers.length) {
if (!(index in readers))
index = 0;
const reader = readers[index];
if (!reader)
break;
const result = await reader.read();
if (result.done)
readers = without(readers, reader);
else {
yield result.value;
index++;
}
}
}
}
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