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streams: fix enqueue race condition on esm modules #40901

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merged 1 commit into from
Dec 21, 2021
Merged

streams: fix enqueue race condition on esm modules #40901

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19 changes: 12 additions & 7 deletions lib/internal/webstreams/readablestream.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1424,13 +1424,18 @@ function readableStreamTee(stream, cloneForBranch2) {
});
},
[kClose]() {
reading = false;
if (!canceled1)
readableStreamDefaultControllerClose(branch1[kState].controller);
if (!canceled2)
readableStreamDefaultControllerClose(branch2[kState].controller);
if (!canceled1 || !canceled2)
cancelPromise.resolve();
// The `process.nextTick()` is not part of the spec.
// This approach was needed to avoid a race condition working with esm
// Further information, see: https://github.com/nodejs/node/issues/39758
process.nextTick(() => {
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No, I meant that opposite. I think https://github.com/nodejs/node/blob/master/lib/internal/streams/end-of-stream.js should be queueMicrotask instead of process.nextTick but I'm not sure 🤔

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I did a simple test by just calling console.log on eos and it doesn't call, so not sure either if the end-of-stream is the best place. Looks like the kClose is suitable for that otherwise my second comment #40901 (comment) is valid.

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Please add a comment here explaining that the addition of the process.nextTick is not part of the spec and why it's needed with a link back to the original issue.

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Done.

reading = false;
if (!canceled1)
readableStreamDefaultControllerClose(branch1[kState].controller);
if (!canceled2)
readableStreamDefaultControllerClose(branch2[kState].controller);
if (!canceled1 || !canceled2)
cancelPromise.resolve();
});
},
[kError]() {
reading = false;
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36 changes: 36 additions & 0 deletions test/parallel/test-whatwg-readablestream.mjs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,36 @@
import { mustCall } from '../common/index.mjs';
import { ReadableStream } from 'stream/web';
import assert from 'assert';

{
// Test tee() with close in the nextTick after enqueue
async function read(stream) {
const chunks = [];
for await (const chunk of stream)
chunks.push(chunk);
return Buffer.concat(chunks).toString();
}

const [r1, r2] = new ReadableStream({
start(controller) {
process.nextTick(() => {
controller.enqueue(new Uint8Array([102, 111, 111, 98, 97, 114]));

process.nextTick(() => {
controller.close();
});
});
}
}).tee();

(async () => {
const [dataReader1, dataReader2] = await Promise.all([
read(r1),
read(r2),
]);

assert.strictEqual(dataReader1, dataReader2);
assert.strictEqual(dataReader1, 'foobar');
assert.strictEqual(dataReader2, 'foobar');
})().then(mustCall());
}