Oilpan: Allocation should be allowed in pre-finalizers

Source/platform/heap/ThreadState.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 54 matching lines @@
 class Visitor;
 
 using Address = uint8_t*;
 
 using FinalizationCallback = void (*)(void*);
 using VisitorCallback = void (*)(Visitor*, void* self);
 using TraceCallback = VisitorCallback;
 using WeakCallback = VisitorCallback;
 using EphemeronCallback = VisitorCallback;
 
-// Declare that a class has a pre-finalizer function.  The function is called in
-// the object's owner thread, and can access Member<>s to other
-// garbage-collected objects allocated in the thread.  However we must not
-// allocate new garbage-collected objects, nor update Member<> and Persistent<>
-// pointers.
+// Declare that a class has a pre-finalizer function. The function is called in

[sof, 2015/06/18 18:14:03]

Thanks; it doesn't have to be 100% complete, but eager finalization adds a twist
wrt allowance to touch heap objects from within a destructor.

[haraken, 2015/06/18 18:54:38]

Updated the comment.

+// the object's owner thread. The pre-finalizer is called before any object gets
+// swept, so it is allowed to touch on-heap objects that may be collected in the
+// GC cycle. If you cannot avoid touching on-heap objects in a destructor (which
+// is not allowed), you can consider using the pre-finalizer for doing that
+// work. The only restriction is that the pre-finalizer must not resurrect
+// dead objects (e.g., store unmarked objects into Members etc).
 //
 // This feature is similar to the HeapHashMap<WeakMember<Foo>, OwnPtr<Disposer>>
 // idiom.  The difference between this and the idiom is that pre-finalizer
 // function is called whenever an object is destructed with this feature.  The
 // HeapHashMap<WeakMember<Foo>, OwnPtr<Disposer>> idiom requires an assumption
 // that the HeapHashMap outlives objects pointed by WeakMembers.
 // FIXME: Replace all of the HeapHashMap<WeakMember<Foo>, OwnPtr<Disposer>>
 // idiom usages with the pre-finalizer if the replacement won't cause
 // performance regressions.
 //
@@ skipping 432 matching lines @@
     void incrementMarkedObjectsAge();
 
     void snapshotFreeListIfNecessary();
 
     void collectAndReportMarkSweepStats() const;
     void reportMarkSweepStats(const char* statsName, const ClassAgeCountsMap&) const;
 #endif
 
     void pushThreadLocalWeakCallback(void*, WeakCallback);
     bool popAndInvokeThreadLocalWeakCallback(Visitor*);
+    void threadLocalWeakProcessing();
 
     size_t objectPayloadSizeForTesting();
     void prepareHeapForTermination();
 
     // Request to call a pref-finalizer of the target object before the object
     // is destructed.  The class T must have USING_PRE_FINALIZER().  The
     // argument should be |*this|.  Registering a lot of objects affects GC
     // performance.  We should register an object only if the object really
     // requires pre-finalizer, and we should unregister the object if
     // pre-finalizer is unnecessary.
@@ skipping 230 matching lines @@
 };
 
 template<> class ThreadStateFor<AnyThread> {
 public:
     static ThreadState* state() { return ThreadState::current(); }
 };
 
 } // namespace blink
 
 #endif // ThreadState_h