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stream: improve performance for sync write finishes

Improve performance and reduce memory usage when a writable stream
is written to with the same callback (which is the most common case)
and when the write operation finishes synchronously (which is also
often the case).

                                                         confidence improvement accuracy (*)    (**)   (***)
    streams/writable-manywrites.js sync='no' n=2000000                  0.99 %       ±3.20%  ±4.28%  ±5.61%
    streams/writable-manywrites.js sync='yes' n=2000000        ***    710.69 %      ±19.65% ±26.47% ±35.09%

Refs: #18013
Refs: #18367

PR-URL: #30710
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
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addaleax authored and MylesBorins committed Nov 29, 2019
1 parent e624bb5 commit ce6a865ab28bf49f7b929772a0938e784bcdee44
@@ -4,14 +4,19 @@ const common = require('../common');
const Writable = require('stream').Writable;

const bench = common.createBenchmark(main, {
n: [2e6]
n: [2e6],
sync: ['yes', 'no']
});

function main({ n }) {
function main({ n, sync }) {
const b = Buffer.allocUnsafe(1024);
const s = new Writable();
sync = sync === 'yes';
s._write = function(chunk, encoding, cb) {
cb();
if (sync)
cb();
else
process.nextTick(cb);
};

bench.start();
@@ -137,6 +137,10 @@ function WritableState(options, stream, isDuplex) {
// The amount that is being written when _write is called.
this.writelen = 0;

// Storage for data passed to the afterWrite() callback in case of
// synchronous _write() completion.
this.afterWriteTickInfo = null;

this.bufferedRequest = null;
this.lastBufferedRequest = null;

@@ -483,22 +487,41 @@ function onwrite(stream, er) {
}

if (sync) {
process.nextTick(afterWrite, stream, state, cb);
// It is a common case that the callback passed to .write() is always
// the same. In that case, we do not schedule a new nextTick(), but rather
// just increase a counter, to improve performance and avoid memory
// allocations.
if (state.afterWriteTickInfo !== null &&
state.afterWriteTickInfo.cb === cb) {
state.afterWriteTickInfo.count++;
} else {
state.afterWriteTickInfo = { count: 1, cb, stream, state };
process.nextTick(afterWriteTick, state.afterWriteTickInfo);
}
} else {
afterWrite(stream, state, cb);
afterWrite(stream, state, 1, cb);
}
}
}

function afterWrite(stream, state, cb) {
function afterWriteTick({ stream, state, count, cb }) {
state.afterWriteTickInfo = null;
return afterWrite(stream, state, count, cb);
}

function afterWrite(stream, state, count, cb) {
const needDrain = !state.ending && !stream.destroyed && state.length === 0 &&
state.needDrain;
if (needDrain) {
state.needDrain = false;
stream.emit('drain');
}
state.pendingcb--;
cb();

while (count-- > 0) {
state.pendingcb--;
cb();
}

finishMaybe(stream, state);
}

@@ -0,0 +1,30 @@
'use strict';
const common = require('../common');
const { Console } = require('console');
const { Writable } = require('stream');
const async_hooks = require('async_hooks');

// Make sure that repeated calls to console.log(), and by extension
// stream.write() for the underlying stream, allocate exactly 1 tick object.
// At the time of writing, that is enough to ensure a flat memory profile
// from repeated console.log() calls, rather than having callbacks pile up
// over time, assuming that data can be written synchronously.
// Refs: https://github.com/nodejs/node/issues/18013
// Refs: https://github.com/nodejs/node/issues/18367

const checkTickCreated = common.mustCall();

async_hooks.createHook({
init(id, type, triggerId, resoure) {
if (type === 'TickObject') checkTickCreated();
}
}).enable();

const console = new Console(new Writable({
write: common.mustCall((chunk, encoding, cb) => {
cb();
}, 100)
}));

for (let i = 0; i < 100; i++)
console.log(i);

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