Improve JSON.stringify perf for TypedArrays #4831

MikeHolman · 2018-03-16T04:06:17Z

During enumeration, we can (and should) avoid creating PropertyRecords for TypedArrays. Instead we can use the numeric index.

In the below micro-benchmark, this improves our perf by about 45%.

const view = new Int8Array(1 << 24);
for (let i = 0; i < view.length; ++i) {
  view[i] = i|0;
}
var start = Date.now();
const str = JSON.stringify(view);
console.log(Date.now() - start);

OS: 16385822

curtisman · 2018-03-16T15:34:47Z

lib/Runtime/Library/JSONStringifier.cpp

@@ -520,18 +552,25 @@ JSONStringifier::ReadObject(_In_ RecyclableObject* obj, _In_ JSONObjectStack* ob
            JavascriptStaticEnumerator enumerator;
            if (obj->GetEnumerator(&enumerator, EnumeratorFlags::SnapShotSemantics | EnumeratorFlags::EphemeralReference, this->scriptContext))
            {
-                enumerator.GetInitialPropertyCount();


You might want to clean up the implementation in JAvascriptStaticEnumerator.h and DynamicObjectPropertyEnumerator.h as well, as I don't see other references to those. #Resolved

curtisman

sethbrenith

akroshg · 2018-03-16T17:05:27Z

lib/Runtime/Library/JSONStringifier.cpp

+    JSONObjectProperty prop;
+    prop.propertyName = propertyName;
+
+    Var value = JavascriptOperators::GetItem(obj, numericIndex, this->scriptContext);


:: [](start = 35, length = 2)

Fantastic wins.

So if I understand - obj is typed array, so this will call to the DirectGetItem of typed array which will have unnecessary checks being detached and others . Could that be avoided (or it is already avoided)?

akroshg · 2018-03-16T17:16:39Z

    if (JavascriptOperators::IsArray(valueObj))

Curious why don't we have similar case like this for typed array and read the index just like an array? #ByDesign

Refers to: lib/Runtime/Library/JSONStringifier.cpp:811 in 45caec1. [](commit_id = 45caec1, deletion_comment = False)

akroshg · 2018-03-16T17:50:27Z

    if (JavascriptOperators::IsArray(valueObj))

It is perfectly fine if you don't want to rush different changes on this PR.

In reply to: 373783535 [](ancestors = 373783535)

Refers to: lib/Runtime/Library/JSONStringifier.cpp:811 in 45caec1. [](commit_id = 45caec1, deletion_comment = False)

MikeHolman · 2018-03-16T19:00:26Z

    if (JavascriptOperators::IsArray(valueObj))

It's because spec has very different way they serialize normal arrays vs. other objects. Normal arrays only serialize elements up to length, but typed arrays will need to serialize all properties (e.g. if i say typedArr.prop = "blah" we need to serialize that). So I'd rather just use the normal enumerator rather than trying to be fancy

In reply to: 373793434 [](ancestors = 373793434,373783535)

Refers to: lib/Runtime/Library/JSONStringifier.cpp:811 in 45caec1. [](commit_id = 45caec1, deletion_comment = False)

Merge pull request #4831 from MikeHolman:arrenum During enumeration, we can (and should) avoid creating PropertyRecords for TypedArrays. Instead we can use the numeric index. In the below micro-benchmark, this improves our perf by about 45%. ```` const view = new Int8Array(1 << 24); for (let i = 0; i < view.length; ++i) { view[i] = i|0; } var start = Date.now(); const str = JSON.stringify(view); console.log(Date.now() - start); ```` OS: 16385822

lookup properties by numeric index for typed arrays during stringify

45caec1

curtisman reviewed Mar 16, 2018

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curtisman approved these changes Mar 16, 2018

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sethbrenith approved these changes Mar 16, 2018

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akroshg reviewed Mar 16, 2018

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fix UT failure; remove unused method

1e918e2

chakrabot merged commit 1e918e2 into chakra-core:master Mar 19, 2018

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Improve JSON.stringify perf for TypedArrays #4831

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MikeHolman commented Mar 16, 2018

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Improve JSON.stringify perf for TypedArrays #4831

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