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Optimize critical I/O path for input latency #4145

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Merged
merged 2 commits into from
Sep 25, 2022
Merged

Optimize critical I/O path for input latency #4145

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c6e4788
Use microtasks on server
Tyriar Sep 24, 2022
0b81208
Prefer microtask to timeout in write queue
Tyriar Sep 24, 2022
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4 changes: 2 additions & 2 deletions demo/server.js
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Original file line number Diff line number Diff line change
Expand Up @@ -86,7 +86,7 @@ function startServer() {
return (data) => {
s += data;
if (!sender) {
sender = setTimeout(() => {
sender = queueMicrotask(() => {
socket.send(s);
s = '';
sender = null;
Expand All @@ -103,7 +103,7 @@ function startServer() {
buffer.push(data);
length += data.length;
if (!sender) {
sender = setTimeout(() => {
sender = queueMicrotask(() => {
socket.send(Buffer.concat(buffer, length));
buffer = [];
sender = null;
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4 changes: 2 additions & 2 deletions src/common/input/WriteBuffer.ts
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Expand Up @@ -105,7 +105,7 @@ export class WriteBuffer {
// schedule chunk processing for next event loop run
if (!this._writeBuffer.length) {
this._bufferOffset = 0;
setTimeout(() => this._innerWrite());
queueMicrotask(() => this._innerWrite());
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@jerch jerch Sep 27, 2022

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This should be safe with queueMicrotask - reason: this code path is only entered, if the write queue was empty before, which guarantees, that there happened a screen refresh before.

}

this._pendingData += data.length;
Expand Down Expand Up @@ -217,7 +217,7 @@ export class WriteBuffer {
this._callbacks = this._callbacks.slice(this._bufferOffset);
this._bufferOffset = 0;
}
setTimeout(() => this._innerWrite());
queueMicrotask(() => this._innerWrite());
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@jerch jerch Sep 27, 2022 •
edited
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Not so sure about queueMicrotask here - imho this will skip any screen refreshs in between, if the write queue never drops empty? (This edge case might be provokable by tiny messages at sync promisified term.write calls while the write queue never drops empty...)

There are more edge cases linked to direct microtask usage - imho chrome and firefox prioritize them differently (dont remember the details atm).

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@Tyriar Tyriar Sep 27, 2022

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Opps. You're right, will fix

There are more edge cases linked to direct microtask usage - imho chrome and firefox prioritize them differently (dont remember the details atm).

I didn't test in Firefox but this should only matter if queueMicrotask ends up slower than setTimeout which I think would be against the spec?

} else {
this._writeBuffer.length = 0;
this._callbacks.length = 0;
Expand Down