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buffer: improve toJSON() performance #10895

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buffer: improve toJSON() performance #10895

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18 changes: 18 additions & 0 deletions benchmark/buffers/buffer-tojson.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
'use strict';

const common = require('../common.js');

const bench = common.createBenchmark(main, {
n: [1e4],
len: [0, 10, 256, 4 * 1024]
});

function main(conf) {
var n = +conf.n;
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@fhalde fhalde Jan 19, 2017 •
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why not use let or const for n and buf to maintain consistency across the codebase

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@mscdex mscdex Jan 19, 2017

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Personally I'd rather just stick to var in benchmark code for the forseeable future. Having issues with let and const in node core code has left a bit of a "bad taste." While it might seem moot in benchmark code, I'd rather not have to worry about deopts making my benchmarks run unnecessarily longer.

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@gibfahn gibfahn Jan 19, 2017

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In addition to what @mscdex said, the current position on const/let over var is "only in code where performance doesn't matter". I'd say it makes more sense for benchmarks/ to be consistent with lib/ than test/.

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@fhalde fhalde Jan 19, 2017

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oh that was something new! Thanks!

var buf = Buffer.allocUnsafe(+conf.len);

bench.start();
for (var i = 0; i < n; ++i)
buf.toJSON();
bench.end(n);
}
12 changes: 8 additions & 4 deletions lib/buffer.js
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Original file line number Diff line number Diff line change
Expand Up @@ -804,10 +804,14 @@ Buffer.prototype.write = function(string, offset, length, encoding) {


Buffer.prototype.toJSON = function() {
return {
type: 'Buffer',
data: Array.prototype.slice.call(this, 0)
};
if (this.length) {
const data = [];
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@evanlucas evanlucas Jan 19, 2017

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Is this faster than using new Array(this.length)?

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@mscdex mscdex Jan 19, 2017

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It is until appropriate backports to V8 5.4 are made. I've just decided to go ahead and use this method. See this issue for more information.

for (var i = 0; i < this.length; ++i)
data[i] = this[i];
return { type: 'Buffer', data };
} else {
return { type: 'Buffer', data: [] };
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@ronkorving ronkorving Jan 19, 2017

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Why the special case at all? The loop would run 0 times if length is 0, and you would get exactly the output you want. I doubt performance would be any different, would it?

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@cjihrig cjihrig Jan 19, 2017

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Unless the difference is really noticeable, I think I'd rather keep this simple and drop the if statement as @ronkorving said.

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@mscdex mscdex Jan 19, 2017 •
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There is a noticeable performance difference, otherwise I wouldn't have bothered. Without checking the IR explicitly, it probably has to do with setting up the loop or similar.

}
};


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