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stream: refactor Writable buffering #30974

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stream: refactor Writable buffering #30974

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11 changes: 8 additions & 3 deletions benchmark/streams/writable-manywrites.js
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Original file line number Diff line number Diff line change
Expand Up @@ -20,8 +20,13 @@ function main({ n, sync }) {
};

bench.start();
for (var k = 0; k < n; ++k) {
s.write(b);

let k = 0;
function run () {
while (k++ < n && s.write(b));
if (k >= n)
bench.end(n);
}
bench.end(n);
s.on('drain', run);
run();
}
162 changes: 48 additions & 114 deletions lib/_stream_writable.js
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Original file line number Diff line number Diff line change
Expand Up @@ -148,8 +148,8 @@ function WritableState(options, stream, isDuplex) {
// synchronous _write() completion.
this.afterWriteTickInfo = null;

this.bufferedRequest = null;
this.lastBufferedRequest = null;
this.buffered = [];
this.buffered.allBuffers = true;

// Number of pending user-supplied write callbacks
// this must be 0 before 'finish' can be emitted
Expand All @@ -172,25 +172,10 @@ function WritableState(options, stream, isDuplex) {
// should return false. This is needed since when autoDestroy
// is disabled we need a way to tell whether the stream has failed.
this.errored = false;

// Count buffered requests
this.bufferedRequestCount = 0;

// Allocate the first CorkedRequest, there is always
// one allocated and free to use, and we maintain at most two
const corkReq = { next: null, entry: null, finish: undefined };
corkReq.finish = onCorkedFinish.bind(undefined, corkReq, this);
this.corkedRequestsFree = corkReq;
}

WritableState.prototype.getBuffer = function getBuffer() {
var current = this.bufferedRequest;
const out = [];
while (current) {
out.push(current);
current = current.next;
}
return out;
return this.buffered;
};

ObjectDefineProperty(WritableState.prototype, 'buffer', {
Expand All @@ -200,6 +185,12 @@ ObjectDefineProperty(WritableState.prototype, 'buffer', {
'instead.', 'DEP0003')
});

Object.defineProperty(WritableState.prototype, 'bufferedRequestCount', {
get() {
return this.buffered.length;
}
});

// Test _writableState for inheritance to account for Duplex streams,
// whose prototype chain only points to Readable.
var realHasInstance;
Expand Down Expand Up @@ -338,11 +329,9 @@ Writable.prototype.uncork = function() {
if (state.corked) {
state.corked--;

if (!state.writing &&
!state.corked &&
!state.bufferProcessing &&
state.bufferedRequest)
if (!state.writing) {
clearBuffer(this, state);
}
}
};

Expand Down Expand Up @@ -427,20 +416,9 @@ function writeOrBuffer(stream, state, isBuf, chunk, encoding, cb) {
state.needDrain = true;

if (state.writing || state.corked || state.errored) {
var last = state.lastBufferedRequest;
state.lastBufferedRequest = {
chunk,
encoding,
isBuf,
callback: cb,
next: null
};
if (last) {
last.next = state.lastBufferedRequest;
} else {
state.bufferedRequest = state.lastBufferedRequest;
}
state.bufferedRequestCount += 1;
const buffered = state.buffered;
buffered.push({ chunk, encoding, callback: cb });
buffered.allBuffers = isBuf && buffered.allBuffers;
} else {
doWrite(stream, state, false, len, chunk, encoding, cb);
}
Expand Down Expand Up @@ -496,10 +474,7 @@ function onwrite(stream, er) {
// Check if we're actually ready to finish, but don't emit yet
var finished = needFinish(state) || stream.destroyed;

if (!finished &&
!state.corked &&
!state.bufferProcessing &&
state.bufferedRequest) {
if (!finished) {
clearBuffer(stream, state);
}

Expand Down Expand Up @@ -544,67 +519,42 @@ function afterWrite(stream, state, count, cb) {

// If there's something in the buffer waiting, then process it
function clearBuffer(stream, state) {
state.bufferProcessing = true;
var entry = state.bufferedRequest;

if (stream._writev && entry && entry.next) {
// Fast case, write everything using _writev()
var l = state.bufferedRequestCount;
var buffer = new Array(l);
var holder = state.corkedRequestsFree;
holder.entry = entry;

var count = 0;
var allBuffers = true;
while (entry) {
buffer[count] = entry;
if (!entry.isBuf)
allBuffers = false;
entry = entry.next;
count += 1;
}
buffer.allBuffers = allBuffers;
const buffered = state.buffered;
const bufferedLength = buffered.length;

doWrite(stream, state, true, state.length, buffer, '', holder.finish);
if (!bufferedLength || state.corked || state.bufferProcessing) {
return;
}

// doWrite is almost always async, defer these to save a bit of time
// as the hot path ends with doWrite
state.bufferProcessing = true;
if (bufferedLength > 1 && stream._writev) {
state.pendingcb++;
state.lastBufferedRequest = null;
if (holder.next) {
state.corkedRequestsFree = holder.next;
holder.next = null;
} else {
var corkReq = { next: null, entry: null, finish: undefined };
corkReq.finish = onCorkedFinish.bind(undefined, corkReq, state);
state.corkedRequestsFree = corkReq;
// doWrite mutates buffered array. Keep a copy of callbacks.
const callbacks = new Array(buffered.length);
for (let n = 0; n < buffered.length; ++n) {
callbacks[n] = buffered[n].callback;
}
state.bufferedRequestCount = 0;
} else {
// Slow case, write chunks one-by-one
while (entry) {
var chunk = entry.chunk;
var encoding = entry.encoding;
var cb = entry.callback;
var len = state.objectMode ? 1 : chunk.length;

doWrite(stream, state, false, len, chunk, encoding, cb);
entry = entry.next;
state.bufferedRequestCount--;
// If we didn't call the onwrite immediately, then
// it means that we need to wait until it does.
// also, that means that the chunk and cb are currently
// being processed, so move the buffer counter past them.
if (state.writing) {
break;

doWrite(stream, state, true, state.length, buffered, '', (err) => {
for (const callback of callbacks) {
state.pendingcb--;
callback(err);
}
});
state.buffered = [];
state.buffered.allBuffers = true;
} else {
let i;
for (i = 0; i < bufferedLength && !state.writing; i++) {
const chunk = buffered[i].chunk;
const encoding = buffered[i].encoding;
const callback = buffered[i].callback;

const len = state.objectMode ? 1 : chunk.length;
doWrite(stream, state, false, len, chunk, encoding, callback);
}

if (entry === null)
state.lastBufferedRequest = null;
buffered.splice(0, i);
}

state.bufferedRequest = entry;
state.bufferProcessing = false;
}

Expand Down Expand Up @@ -665,9 +615,9 @@ ObjectDefineProperty(Writable.prototype, 'writableLength', {

function needFinish(state) {
return (state.ending &&
state.length === 0 &&
!state.length &&
!state.buffered.length &&
!state.errored &&
state.bufferedRequest === null &&
!state.finished &&
!state.writing);
}
Expand Down Expand Up @@ -742,20 +692,6 @@ function endWritable(stream, state, cb) {
stream.writable = false;
}

function onCorkedFinish(corkReq, state, err) {
var entry = corkReq.entry;
corkReq.entry = null;
while (entry) {
var cb = entry.callback;
state.pendingcb--;
cb(err);
entry = entry.next;
}

// Reuse the free corkReq.
state.corkedRequestsFree.next = corkReq;
}

function onFinished(stream, state, cb) {
if (state.destroyed && state.errorEmitted) {
// TODO(ronag): Backwards compat. Should be moved to end() without
Expand Down Expand Up @@ -828,12 +764,10 @@ const destroy = destroyImpl.destroy;
Writable.prototype.destroy = function(err, cb) {
const state = this._writableState;
if (!state.destroyed) {
for (let entry = state.bufferedRequest; entry; entry = entry.next) {
for (const entry of state.buffered) {
process.nextTick(entry.callback, new ERR_STREAM_DESTROYED('write'));
}
state.bufferedRequest = null;
state.lastBufferedRequest = null;
state.bufferedRequestCount = 0;
state.buffered = [];
}
destroy.call(this, err, cb);
return this;
Expand Down