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n-api: finalize during second-pass callback #25992

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n-api: finalize during second-pass callback #25992

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n-api: finalize during second-pass callback 
Calling into the engine from a weak callback is unsafe, however, the
engine offers a way to attach a second-pass weak callback which gets
called when it is safe to call into JavaScript. This moves the point
at which the N-API finalize callback gets called to this latter point.

Fixes: #25927
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Gabriel Schulhof committed Feb 7, 2019
commit cf043b3821dae559832b4ae43b2df8a0ed524072
15 changes: 15 additions & 0 deletions src/js_native_api_v8.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -281,10 +281,25 @@ class Reference : private Finalizer {
}

private:
// The N-API finalizer callback may make calls into the engine. V8's heap is
// not in a consistent state during the weak callback, and therefore it does
// not support calls back into it. However, it provides a mechanism for adding
// a finalizer which may make calls back into the engine by allowing us to
// attach such a second-pass finalizer from the first pass finalizer. Thus,
// we do that here to ensure that the N-API finalizer callback is free to call
// into the engine.
static void FinalizeCallback(const v8::WeakCallbackInfo<Reference>& data) {
Reference* reference = data.GetParameter();

// The reference must be reset during the first pass.
reference->_persistent.Reset();

data.SetSecondPassCallback(SecondPassCallback);
}

static void SecondPassCallback(const v8::WeakCallbackInfo<Reference>& data) {
Reference* reference = data.GetParameter();

napi_env env = reference->_env;

if (reference->_finalize_callback != nullptr) {
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