Make AdjustAmountOfExternalAllocatedMemory() more robust.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 954f82144135a95cf2832a5cf90c135c7ab96135..f3f5b16914ea2c5f4a146575f8dc3f06a587b58b 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -5275,8 +5275,9 @@ void V8::AddImplicitReferences(Persistent<Object> parent,
 
 
 intptr_t V8::AdjustAmountOfExternalAllocatedMemory(intptr_t change_in_bytes) {
-  i::Isolate* isolate = i::Isolate::Current();
-  if (IsDeadCheck(isolate, "v8::V8::AdjustAmountOfExternalAllocatedMemory()")) {
+  i::Isolate* isolate = i::Isolate::UncheckedCurrent();
+  if (isolate == NULL || !isolate->IsInitialized() ||

[Erik Corry, 2012/08/07 07:32:13]

This seems a bit fragile.  If we are silently ignoring some updates then the
external memory count will become incorrect.  This will manifest itself as very
poor performance caused by too frequent GCs.  Perhaps it is better to let it
crash and fix whatever it is that is calling from the wrong thread?

[ulan, 2012/08/07 09:05:52]

It's tricky with all those transfers between threads. We want this function to
be a no-op if called from the wrong thread, otherwise we would have to add guard
in each thread:
if (is_v8_initialized()) AdjustAmountOfExternalAllocatedMemory();

At the moment GC is triggered based on the delta of externally allocated  memory
since the last GC (the absolute value of externally allocated memory doesn't
matter). So even if we occasionally miss some updates, this error won't spread
beyond one GC. Of course if we change our heuristics to depend on absolute value
of external memory then we will have a problem.

+      IsDeadCheck(isolate, "v8::V8::AdjustAmountOfExternalAllocatedMemory()")) {
     return 0;
   }
   return isolate->heap()->AdjustAmountOfExternalAllocatedMemory(