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events: optimize condition for optimal scenario #20452

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282749f
events: optimize condition for optimal scenario
apapirovski May 1, 2018
71a1aa1
fixup: simplify conditional further
apapirovski May 2, 2018
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events: optimize condition for optimal scenario 
Instead of always checking whether we've already warned about a
possible EventEmitter memory leak, first run the rest of the
code as accessing random properties on an Array is expensive.
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@apapirovski
apapirovski committed May 1, 2018
commit 282749f26e2cd4b9b9c064242eef4ec2fbc82353
2 changes: 1 addition & 1 deletion benchmark/events/ee-add-remove.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@
const common = require('../common.js');
const events = require('events');

const bench = common.createBenchmark(main, { n: [25e4] });
const bench = common.createBenchmark(main, { n: [1e6] });

function main({ n }) {
const ee = new events.EventEmitter();
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30 changes: 14 additions & 16 deletions lib/events.js
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Expand Up @@ -235,22 +235,20 @@ function _addListener(target, type, listener, prepend) {
}

// Check for listener leak
if (!existing.warned) {
m = $getMaxListeners(target);
if (m && m > 0 && existing.length > m) {
existing.warned = true;
// No error code for this since it is a Warning
// eslint-disable-next-line no-restricted-syntax
const w = new Error('Possible EventEmitter memory leak detected. ' +
`${existing.length} ${String(type)} listeners ` +
'added. Use emitter.setMaxListeners() to ' +
'increase limit');
w.name = 'MaxListenersExceededWarning';
w.emitter = target;
w.type = type;
w.count = existing.length;
process.emitWarning(w);
}
m = $getMaxListeners(target);
if (m && m > 0 && existing.length > m && !existing.warned) {
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@bnoordhuis bnoordhuis May 2, 2018

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If you have time and inclination to test: does reducing m && m > 0 to m > 0 make a difference?

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@apapirovski apapirovski May 2, 2018

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Not sure if it makes a difference yet but it seems a harmless change and simplifies the conditional further. I don't see why we shouldn't do it.

existing.warned = true;
// No error code for this since it is a Warning
// eslint-disable-next-line no-restricted-syntax
const w = new Error('Possible EventEmitter memory leak detected. ' +
`${existing.length} ${String(type)} listeners ` +
'added. Use emitter.setMaxListeners() to ' +
'increase limit');
w.name = 'MaxListenersExceededWarning';
w.emitter = target;
w.type = type;
w.count = existing.length;
process.emitWarning(w);
}
}

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