Oilpan: Add support of pre-finalization callback to Oilpan infrastructure.

Source/platform/heap/ThreadState.h

Index: Source/platform/heap/ThreadState.h
diff --git a/Source/platform/heap/ThreadState.h b/Source/platform/heap/ThreadState.h
index 2513756aae2b550b1871a7f1c07efebffb3c35b5..dfd4076afb2e169e9eb56653dbb03a1e80ea86fe 100644
--- a/Source/platform/heap/ThreadState.h
+++ b/Source/platform/heap/ThreadState.h
@@ -34,6 +34,7 @@
 #include "platform/PlatformExport.h"
 #include "platform/heap/AddressSanitizer.h"
 #include "public/platform/WebThread.h"
+#include "wtf/HashMap.h"
 #include "wtf/HashSet.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
@@ -42,10 +43,6 @@
 #include "wtf/ThreadingPrimitives.h"
 #include "wtf/Vector.h"
 
-#if ENABLE(GC_PROFILE_HEAP)
-#include "wtf/HashMap.h"
-#endif
-
 namespace blink {
 
 class BaseHeap;
@@ -131,6 +128,39 @@ struct ThreadingTrait {
 
 template<typename U> class ThreadingTrait<const U> : public ThreadingTrait<U> { };
 
+// Declare that a class has a pre-finalizer function.  The function can access
+// other garbarge-collected members.  However we must not allocate

[haraken, 2014/10/03 06:00:32]

Slightly clearer:

(a) The function can access garbage-collected objects allocated on the thread
heap.
(b) The function cannot access garbage-collected objects allocated on other
thread heaps.
(c) The function cannot allocate garbage-collected objects.
(d) The function cannot change an object graph.

(Note related to CL: We already have an assert for (c). Would it be possible to
add an assert for (b) and (d)? I think we can hook Member::operator->,
Member::operator= etc, but I'm a bit afraid that adding an assert to
Member::operator-> etc will unacceptably slow down performance of Debug builds.)

[tkent, 2014/10/03 06:34:01]

(A), (b), (c), and (d) are correct.  I should add them to the code comment.

I also think complexity to detect (b) and (d) would be unacceptable. These
restrictions are same as the existing HashMap<WeakMember<>> pattern, which is
working well now. So documentation would be enough.

[haraken, 2014/10/03 06:39:18]

Agreed.

+// garbage-collected objects, and must not change content of Member<> and
+// Persistent<>.
+// See ThreadState::registerObjectWithPreFinalizer.
+//
+// Usage:
+//
+// class Foo : GarbageCollected<Foo> {
+//     USING_PRE_FINALIZATION_CALLBACK(Foo, dispose);
+// public:
+//     Foo() ....
+// private:
+//     Member<Bar> m_bar;
+// };
+//
+// void Foo::dispose()
+// {
+//     m_bar->...
+// }
+#define USING_PRE_FINALIZATION_CALLBACK(Class, method)   \

[haraken, 2014/10/03 06:00:31]

USING_PRE_FINALIZATION_CALLBACK => USING_PRE_FINALIZER ?

(Another possible name would be USING_NEAR_DEATH_CALLBACK. I don't have a strong
opinion here. V8 is using "near-death" notifications.)

[tkent, 2014/10/06 01:25:53]

Done.

+    public: \
+    static bool willFinalizeDeadGarbageCollectedObject(void* object, Visitor& visitor)   \

[tkent, 2014/10/03 05:34:26]

wrong indentation.   will fix.

[haraken, 2014/10/03 06:00:31]

willFinalizeDeadGarbageCollectedObject => invokePreFinalizer ?

[tkent, 2014/10/03 06:34:01]

Yeah, it's inconsistent with other names in this patch though I wanted to make
this consistent with GarbageCollectedFinalized::finalizeGarbageCollectedObject.
invokePreFinalizerOfGarbageCollectedObject?

[haraken, 2014/10/03 06:39:18]

I don't have a strong opinion here, but I guess invokePreFinalizer would be
enough and consistent with invokePreFinalizers.

[tkent, 2014/10/06 01:25:53]

Done.

+        { \
+            Class* self = reinterpret_cast<Class*>(object); \
+            if (visitor.isAlive(self)) \
+                return false; \
+            self->method(); \
+            return true; \
+        } \
+    private: \
+        void method()

[Erik Corry, 2014/10/03 09:13:26]

To my mind, declaring the method in the macro like this puts more magic in the
macro than it needs to have.  It's not much work to declare the method
explicitly, and makes the code easier to navigate. Otherwise the reader is left
wondering where this 'dispose' method comes from.

If you were willing to fix the name of the 'dispose' method you could probably
remove this ugly macro completely, and replace it with a single templatized
static method outside the classes. That would mean the dispose method needed to
be public, which I think is OK, since it is essentially called from outside the
object (by the GC infrastructure).

[tkent, 2014/10/06 01:25:53]

Removed the hidden declaration.

+
 // List of typed heaps. The list is used to generate the implementation
 // of typed heap related methods.
 //
@@ -629,6 +659,27 @@ public:
     void registerSweepingTask();
     void unregisterSweepingTask();
 
+    // Request to call a pref-finalize function of the target object before the

[haraken, 2014/10/03 06:00:31]

pre-finalizer

[tkent, 2014/10/06 01:25:53]

Done.

+    // object is destructed. The class T must have
+    // USING_PRE_FINALIZATION_CALLBACK().  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.
+    template<typename T>
+    void registerObjectWithPreFinalizer(T& target)

[haraken, 2014/10/03 06:00:31]

registerObjectWithPreFinalizer => registerPreFinalizer ?

[tkent, 2014/10/06 01:25:53]

Done.

+    {
+        ASSERT(!m_objectsWithPreFinalizer.contains(&target));

[haraken, 2014/10/03 06:00:31]

Shall we add ASSERT(!isSweepInProgress()) ?

[tkent, 2014/10/06 01:25:53]

Done.

+        m_objectsWithPreFinalizer.add(&target, &T::willFinalizeDeadGarbageCollectedObject);
+    }
+    // Cancel above requests.  The argument should be |*this|.  This function is
+    // ignored if it is called in pre-finalizer functions.
+    template<typename T>
+    void unregisterObjectWithPreFinalizer(T& target)

[haraken, 2014/10/03 06:00:32]

unregisterObjectWithPreFinalizer => unregisterPreFinalizer ?

[tkent, 2014/10/06 01:25:53]

Done.

+    {
+        ASSERT(&T::willFinalizeDeadGarbageCollectedObject);
+        unregisterObjectWithPreFinalizerInternal(&target);
+    }
+
     Mutex& sweepMutex() { return m_sweepMutex; }
 
 private:
@@ -667,6 +718,8 @@ private:
     void setLowCollectionRate(bool value) { m_lowCollectionRate = value; }
 
     void waitUntilSweepersDone();
+    void unregisterObjectWithPreFinalizerInternal(void*);
+    void invokePreFinalizer(Visitor&);

[haraken, 2014/10/03 06:00:32]

invokePreFinalizer => invokePreFinalizers ?

[tkent, 2014/10/06 01:25:53]

Done.

 
     static WTF::ThreadSpecific<ThreadState*>* s_threadSpecific;
     static SafePointBarrier* s_safePointBarrier;
@@ -718,6 +771,7 @@ private:
     ThreadCondition m_sweepThreadCondition;
 
     CallbackStack* m_weakCallbackStack;
+    HashMap<void*, bool (*)(void*, Visitor&)> m_objectsWithPreFinalizer;

[haraken, 2014/10/03 06:00:32]

m_objectsWithPreFinalizer => m_preFinalizers ?

[tkent, 2014/10/06 01:25:53]

Done.

 
 #if defined(ADDRESS_SANITIZER)
     void* m_asanFakeStack;