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src: do not cache NumberOfHeapSpaces() globally #20971

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src: do not cache NumberOfHeapSpaces() globally #20971

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src: do not cache `NumberOfHeapSpaces()` globally
addaleax May 25, 2018
f26c89c
[squash] bnoordhuis suggestion
addaleax May 26, 2018
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src: do not cache NumberOfHeapSpaces() globally 
While `NumberOfHeapSpaces()` currently returns a constant value,
that is not strictly guaranteed by the V8 API as far as I can tell.
Therefore, caching it globally does not seem appropriate.

(The motivation here is that this squelches warnings which are
produced by concurrency debugging tooling due to the apparent
race conditions when accessing the global variable.)
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addaleax committed May 25, 2018
commit 0df7dec197eabc571823561374a0f43b7f950c58
7 changes: 2 additions & 5 deletions src/node_v8.cc
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Expand Up @@ -71,9 +71,6 @@ static const size_t kHeapSpaceStatisticsPropertiesCount =
HEAP_SPACE_STATISTICS_PROPERTIES(V);
#undef V

// Will be populated in InitializeV8Bindings.
static size_t number_of_heap_spaces = 0;


void CachedDataVersionTag(const FunctionCallbackInfo<Value>& args) {
Environment* env = Environment::GetCurrent(args);
Expand Down Expand Up @@ -101,7 +98,7 @@ void UpdateHeapSpaceStatisticsBuffer(const FunctionCallbackInfo<Value>& args) {
Isolate* const isolate = env->isolate();
double* buffer = env->heap_space_statistics_buffer();

for (size_t i = 0; i < number_of_heap_spaces; i++) {
for (size_t i = 0; i < isolate->NumberOfHeapSpaces(); i++) {
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@bnoordhuis bnoordhuis May 26, 2018

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Suggestion: cache the value in a local so it's only one function call instead of n function calls.

isolate->GetHeapSpaceStatistics(&s, i);
size_t const property_offset = i * kHeapSpaceStatisticsPropertiesCount;
#define V(index, name, _) buffer[property_offset + index] = \
Expand Down Expand Up @@ -153,7 +150,7 @@ void Initialize(Local<Object> target,
Uint32::NewFromUnsigned(env->isolate(),
kHeapSpaceStatisticsPropertiesCount));

number_of_heap_spaces = env->isolate()->NumberOfHeapSpaces();
size_t number_of_heap_spaces = env->isolate()->NumberOfHeapSpaces();

// Heap space names are extracted once and exposed to JavaScript to
// avoid excessive creation of heap space name Strings.
Expand Down