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events: improve performance for emit(), on(), and listeners() #13155

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events: improve performance for emit(), on(), and listeners() #13155

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8366e7e
events: improve listeners() performance
mscdex May 23, 2017
d3e3ade
events: improve on() performance
mscdex May 23, 2017
9c7d3b0
events: improve emit() performance
mscdex May 23, 2017
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18 changes: 10 additions & 8 deletions benchmark/events/ee-add-remove.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,24 +2,26 @@
var common = require('../common.js');
var events = require('events');

var bench = common.createBenchmark(main, {n: [25e4]});
var bench = common.createBenchmark(main, {n: [25e4], listeners: [10]});

function main(conf) {
var n = conf.n | 0;
var listeners = conf.listeners | 0;

var ee = new events.EventEmitter();
var listeners = [];
ee.setMaxListeners(listeners + 1);
var fns = [];

var k;
for (k = 0; k < 10; k += 1)
listeners.push(function() {});
for (k = 0; k < listeners; k += 1)
fns.push(function() { return 0; });

bench.start();
for (var i = 0; i < n; i += 1) {
for (k = listeners.length; --k >= 0; /* empty */)
ee.on('dummy', listeners[k]);
for (k = listeners.length; --k >= 0; /* empty */)
ee.removeListener('dummy', listeners[k]);
for (k = listeners; --k >= 0; /* empty */)
ee.on('dummy', fns[k]);
for (k = listeners; --k >= 0; /* empty */)
ee.removeListener('dummy', fns[k]);
}
bench.end(n);
}
8 changes: 5 additions & 3 deletions benchmark/events/ee-emit.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,15 +2,17 @@
var common = require('../common.js');
var EventEmitter = require('events').EventEmitter;

var bench = common.createBenchmark(main, {n: [2e6]});
var bench = common.createBenchmark(main, {n: [2e6], listeners: [10]});

function main(conf) {
var n = conf.n | 0;
var listeners = conf.listeners | 0;

var ee = new EventEmitter();
ee.setMaxListeners(listeners + 1);

for (var k = 0; k < 10; k += 1)
ee.on('dummy', function() {});
for (var k = 0; k < listeners; k += 1)
ee.on('dummy', function() { return 0; });

bench.start();
for (var i = 0; i < n; i += 1) {
Expand Down
21 changes: 0 additions & 21 deletions benchmark/events/ee-listeners-many.js
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8 changes: 5 additions & 3 deletions benchmark/events/ee-listeners.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,15 +2,17 @@
var common = require('../common.js');
var EventEmitter = require('events').EventEmitter;

var bench = common.createBenchmark(main, {n: [5e6]});
var bench = common.createBenchmark(main, {n: [5e6], listeners: [10, 100]});

function main(conf) {
var n = conf.n | 0;
var listeners = conf.listeners | 0;

var ee = new EventEmitter();
ee.setMaxListeners(listeners + 1);

for (var k = 0; k < 10; k += 1)
ee.on('dummy', function() {});
for (var k = 0; k < listeners; k += 1)
ee.on('dummy', function() { return 0; });

bench.start();
for (var i = 0; i < n; i += 1) {
Expand Down
205 changes: 114 additions & 91 deletions lib/events.js
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Original file line number Diff line number Diff line change
Expand Up @@ -86,74 +86,18 @@ EventEmitter.prototype.setMaxListeners = function setMaxListeners(n) {
};

function $getMaxListeners(that) {
if (that._maxListeners === undefined)
const maxListeners = that._maxListeners;
if (maxListeners === undefined)
return EventEmitter.defaultMaxListeners;
return that._maxListeners;
return maxListeners;
}

EventEmitter.prototype.getMaxListeners = function getMaxListeners() {
return $getMaxListeners(this);
};

// These standalone emit* functions are used to optimize calling of event
// handlers for fast cases because emit() itself often has a variable number of
// arguments and can be deoptimized because of that. These functions always have
// the same number of arguments and thus do not get deoptimized, so the code
// inside them can execute faster.
function emitNone(handler, isFn, self) {
if (isFn)
handler.call(self);
else {
var len = handler.length;
var listeners = arrayClone(handler, len);
for (var i = 0; i < len; ++i)
listeners[i].call(self);
}
}
function emitOne(handler, isFn, self, arg1) {
if (isFn)
handler.call(self, arg1);
else {
var len = handler.length;
var listeners = arrayClone(handler, len);
for (var i = 0; i < len; ++i)
listeners[i].call(self, arg1);
}
}
function emitTwo(handler, isFn, self, arg1, arg2) {
if (isFn)
handler.call(self, arg1, arg2);
else {
var len = handler.length;
var listeners = arrayClone(handler, len);
for (var i = 0; i < len; ++i)
listeners[i].call(self, arg1, arg2);
}
}
function emitThree(handler, isFn, self, arg1, arg2, arg3) {
if (isFn)
handler.call(self, arg1, arg2, arg3);
else {
var len = handler.length;
var listeners = arrayClone(handler, len);
for (var i = 0; i < len; ++i)
listeners[i].call(self, arg1, arg2, arg3);
}
}

function emitMany(handler, isFn, self, args) {
if (isFn)
handler.apply(self, args);
else {
var len = handler.length;
var listeners = arrayClone(handler, len);
for (var i = 0; i < len; ++i)
listeners[i].apply(self, args);
}
}

EventEmitter.prototype.emit = function emit(type) {
var er, handler, len, args, i, events, domain;
var er, fn, i, events, domain;
var needDomainExit = false;
var doError = (type === 'error');

Expand Down Expand Up @@ -189,38 +133,103 @@ EventEmitter.prototype.emit = function emit(type) {
return false;
}

handler = events[type];
fn = events[type];

if (!handler)
if (!fn)
return false;

if (domain && this !== process) {
domain.enter();
needDomainExit = true;
}

var isFn = typeof handler === 'function';
len = arguments.length;
switch (len) {
// fast cases
case 1:
emitNone(handler, isFn, this);
break;
case 2:
emitOne(handler, isFn, this, arguments[1]);
break;
case 3:
emitTwo(handler, isFn, this, arguments[1], arguments[2]);
break;
case 4:
emitThree(handler, isFn, this, arguments[1], arguments[2], arguments[3]);
break;
// slower
default:
args = new Array(len - 1);
for (i = 1; i < len; i++)
args[i - 1] = arguments[i];
emitMany(handler, isFn, this, args);
var len = arguments.length;
var args;
if (typeof fn === 'function') {
switch (len) {
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Maybe if simplified to will be faster?

EventEmitter.prototype.emit = function emit(type, ...args) {
  /* code */
  fn.call(this, ...args);
  /* code */
}

case 1: fn.call(this); break;
case 2: fn.call(this, arguments[1]); break;
case 3: fn.call(this, arguments[1], arguments[2]); break;
case 4: fn.call(this, arguments[1], arguments[2], arguments[3]);
break;
default:
args = new Array(len - 1);
for (i = 1; i < len; i++)
args[i - 1] = arguments[i];
fn.apply(this, args);
}
} else {
var fnlen = fn.length;
fn = arrayClone(fn, fnlen);
switch (len) {
case 1:
fn[0].call(this);
fn[1].call(this);
if (fnlen === 2) break;
fn[2].call(this);
if (fnlen === 3) break;
fn[3].call(this);
if (fnlen === 4) break;
fn[4].call(this);
if (fnlen === 5) break;
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if (fnlen === 5) [](start = 7, length = 17)

Is there any significance of unrolling the loop for 5 ? Or is it that in most common scenario there are not more than 5 event handlers to trigger? Either case, could you write a comment about it?

for (i = 5; i < fnlen; ++i)
fn[i].call(this);
break;
case 2:
fn[0].call(this, arguments[1]);
fn[1].call(this, arguments[1]);
if (fnlen === 2) break;
fn[2].call(this, arguments[1]);
if (fnlen === 3) break;
fn[3].call(this, arguments[1]);
if (fnlen === 4) break;
fn[4].call(this, arguments[1]);
if (fnlen === 5) break;
for (i = 5; i < fnlen; ++i)
fn[i].call(this, arguments[1]);
break;
case 3:
fn[0].call(this, arguments[1], arguments[2]);
fn[1].call(this, arguments[1], arguments[2]);
if (fnlen === 2) break;
fn[2].call(this, arguments[1], arguments[2]);
if (fnlen === 3) break;
fn[3].call(this, arguments[1], arguments[2]);
if (fnlen === 4) break;
fn[4].call(this, arguments[1], arguments[2]);
if (fnlen === 5) break;
for (i = 5; i < fnlen; ++i)
fn[i].call(this, arguments[1], arguments[2]);
break;
case 4:
fn[0].call(this, arguments[1], arguments[2], arguments[3]);
fn[1].call(this, arguments[1], arguments[2], arguments[3]);
if (fnlen === 2) break;
fn[2].call(this, arguments[1], arguments[2], arguments[3]);
if (fnlen === 3) break;
fn[3].call(this, arguments[1], arguments[2], arguments[3]);
if (fnlen === 4) break;
fn[4].call(this, arguments[1], arguments[2], arguments[3]);
if (fnlen === 5) break;
for (i = 5; i < fnlen; ++i)
fn[i].call(this, arguments[1], arguments[2], arguments[3]);
break;
default:
args = new Array(len - 1);
for (i = 1; i < len; i++)
args[i - 1] = arguments[i];
fn[0].apply(this, args);
fn[1].apply(this, args);
if (fnlen === 2) break;
fn[2].apply(this, args);
if (fnlen === 3) break;
fn[3].apply(this, args);
if (fnlen === 4) break;
fn[4].apply(this, args);
if (fnlen === 5) break;
for (i = 5; i < fnlen; ++i)
fn[i].apply(this, args);
}
}

if (needDomainExit)
Expand All @@ -230,7 +239,6 @@ EventEmitter.prototype.emit = function emit(type) {
};

function _addListener(target, type, listener, prepend) {
var m;
var events;
var existing;

Expand Down Expand Up @@ -275,7 +283,7 @@ function _addListener(target, type, listener, prepend) {

// Check for listener leak
if (!existing.warned) {
m = $getMaxListeners(target);
const m = $getMaxListeners(target);
if (m && m > 0 && existing.length > m) {
existing.warned = true;
const w = new Error('Possible EventEmitter memory leak detected. ' +
Expand Down Expand Up @@ -497,16 +505,31 @@ function spliceOne(list, index) {
}

function arrayClone(arr, n) {
var copy = new Array(n);
switch (n) {
case 2: return [arr[0], arr[1]];
case 3: return [arr[0], arr[1], arr[2]];
case 4: return [arr[0], arr[1], arr[2], arr[3]];
case 5: return [arr[0], arr[1], arr[2], arr[3], arr[4]];
}
const copy = new Array(n);
for (var i = 0; i < n; ++i)
copy[i] = arr[i];
return copy;
}

function unwrapListeners(arr) {
const ret = new Array(arr.length);
for (var i = 0; i < ret.length; ++i) {
ret[i] = arr[i].listener || arr[i];
const first = arr[0].listener || arr[0];
const second = arr[1].listener || arr[1];
const n = arr.length;
switch (n) {
case 2: return [first, second];
case 3: return [first, second, arr[2].listener || arr[2]];
case 4: return [first, second, arr[2].listener || arr[2],
arr[3].listener || arr[3]];
default:
const copy = new Array(n);
for (var i = 0; i < n; ++i)
copy[i] = arr[i].listener || arr[i];
return copy;
}
return ret;
}
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