third_party/WebKit/Source/platform/heap/MarkingVisitorImpl.h

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef MarkingVisitorImpl_h
#define MarkingVisitorImpl_h

#include "platform/heap/Heap.h"
#include "platform/heap/ThreadState.h"
#include "platform/heap/Visitor.h"
#include "wtf/Allocator.h"

namespace blink {

template <typename Derived>
class MarkingVisitorImpl {
    USING_FAST_MALLOC(MarkingVisitorImpl);
protected:
    inline void markHeader(HeapObjectHeader* header, const void* objectPointer, TraceCallback callback)
    {
        ASSERT(header);
        ASSERT(objectPointer);
        if (!toDerived()->shouldMarkObject(objectPointer))
            return;

        // If you hit this ASSERT, it means that there is a dangling pointer
        // from a live thread heap to a dead thread heap.  We must eliminate
        // the dangling pointer.
        // Release builds don't have the ASSERT, but it is OK because
        // release builds will crash in the following header->isMarked()
        // because all the entries of the orphaned arenas are zapped.
        ASSERT(!pageFromObject(objectPointer)->orphaned());

        if (header->isMarked())
            return;

        ASSERT(ThreadState::current()->isInGC());
        ASSERT(toDerived()->getMarkingMode() != Visitor::WeakProcessing);

        // A GC should only mark the objects that belong in its heap.
        DCHECK(&pageFromObject(objectPointer)->arena()->getThreadState()->heap() == &toDerived()->heap());

        header->mark();

        if (callback)
            toDerived()->heap().pushTraceCallback(const_cast<void*>(objectPointer), callback);
    }

    inline void mark(const void* objectPointer, TraceCallback callback)
    {
        if (!objectPointer)
            return;
        HeapObjectHeader* header = HeapObjectHeader::fromPayload(objectPointer);
        markHeader(header, header->payload(), callback);
    }

    inline void registerDelayedMarkNoTracing(const void* objectPointer)
    {
        ASSERT(toDerived()->getMarkingMode() != Visitor::WeakProcessing);
        toDerived()->heap().pushPostMarkingCallback(const_cast<void*>(objectPointer), &markNoTracingCallback);
    }

    inline void registerWeakMembers(const void* closure, const void* objectPointer, WeakCallback callback)
    {
        ASSERT(toDerived()->getMarkingMode() != Visitor::WeakProcessing);
        // We don't want to run weak processings when taking a snapshot.
        if (toDerived()->getMarkingMode() == Visitor::SnapshotMarking)
            return;
        toDerived()->heap().pushThreadLocalWeakCallback(const_cast<void*>(closure), const_cast<void*>(objectPointer), callback);
    }

    inline void registerWeakTable(const void* closure, EphemeronCallback iterationCallback, EphemeronCallback iterationDoneCallback)
    {
        ASSERT(toDerived()->getMarkingMode() != Visitor::WeakProcessing);
        toDerived()->heap().registerWeakTable(const_cast<void*>(closure), iterationCallback, iterationDoneCallback);
    }

#if ENABLE(ASSERT)
    inline bool weakTableRegistered(const void* closure)
    {
        return toDerived()->heap().weakTableRegistered(closure);
    }
#endif

    inline bool ensureMarked(const void* objectPointer)
    {
        if (!objectPointer)
            return false;
        if (!toDerived()->shouldMarkObject(objectPointer))
            return false;
#if ENABLE(ASSERT)
        if (HeapObjectHeader::fromPayload(objectPointer)->isMarked())
            return false;

        toDerived()->markNoTracing(objectPointer);
#else
        // Inline what the above markNoTracing() call expands to,
        // so as to make sure that we do get all the benefits.
        HeapObjectHeader* header = HeapObjectHeader::fromPayload(objectPointer);
        if (header->isMarked())
            return false;
        header->mark();
#endif
        return true;
    }

    inline void registerWeakCellWithCallback(void** cell, WeakCallback callback)
    {
        ASSERT(toDerived()->getMarkingMode() != Visitor::WeakProcessing);
        // We don't want to run weak processings when taking a snapshot.
        if (toDerived()->getMarkingMode() == Visitor::SnapshotMarking)
            return;
        toDerived()->heap().pushGlobalWeakCallback(cell, callback);
    }

    Derived* toDerived()
    {
        return static_cast<Derived*>(this);
    }

private:
    static void markNoTracingCallback(Visitor* visitor, void* object)
    {
        visitor->markNoTracing(object);
    }
};

} // namespace blink

#endif