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stream: improve read() performance more #28989

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Aug 9, 2019
Merged

stream: improve read() performance more #28989

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5 changes: 4 additions & 1 deletion lib/internal/streams/buffer_list.js
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Original file line number Diff line number Diff line change
Expand Up @@ -139,7 +139,10 @@ module.exports = class BufferList {
while (p = p.next) {
const buf = p.data;
const nb = (n > buf.length ? buf.length : n);
buf.copy(ret, ret.length - n, 0, nb);
if (nb === buf.length)
ret.set(buf, ret.length - n);
else
ret.set(new Uint8Array(buf.buffer, buf.byteOffset, nb), ret.length - n);
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how does this differ from copy?

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It's a tad faster.

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yes, just confused as two how it can be faster. Some V8 thingy?

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yes. v8 can optimize the stuff it provides, but our buffer copy is basically a black box to it, since its written in c++. we could probably optimize our copy impl to use typedarray's set if there are no source offsets passed.

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wouldn't it better to apply this there then?

n -= nb;
if (n === 0) {
if (nb === buf.length) {
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