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/*
* Copyright (C) 2013 Apple 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:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include <wtf/DeferrableRefCounted.h>
#include <wtf/Forward.h>
namespace JSC {
class JSCell;
// A C-heap-allocated object that may have additional reference counts
// due to incoming references from the heap, which are tracked in
// reverse: the object knows its incoming references. Such objects also
// have the invariant that they don't have references back into the GC
// heap.
template<typename T>
class GCIncomingRefCounted : public DeferrableRefCounted<T> {
public:
GCIncomingRefCounted()
: m_encodedPointer(0)
{
}
~GCIncomingRefCounted()
{
if (hasVectorOfCells())
delete vectorOfCells();
}
size_t numberOfIncomingReferences() const
{
if (!hasAnyIncoming())
return 0;
if (hasSingleton())
return 1;
return vectorOfCells()->size();
}
JSCell* incomingReferenceAt(size_t index) const
{
ASSERT(hasAnyIncoming());
if (hasSingleton()) {
ASSERT(!index);
return singleton();
}
return vectorOfCells()->at(index);
}
// It's generally not a good idea to call this directly, since if this
// returns true, you're supposed to add this object to the GC's list.
// Call GCIncomingRefCountedSet::addReference() instead.
bool addIncomingReference(JSCell*);
// A filter function returns true if we wish to keep the incoming
// reference, and false if we don't. This may delete the object,
// and if it does so, this returns true. In general, you don't want
// to use this with a filter function that can return false unless
// you're also walking the GC's list.
template<typename FilterFunctionType>
bool filterIncomingReferences(FilterFunctionType&&);
private:
static uintptr_t singletonFlag() { return 1; }
bool hasVectorOfCells() const { return !(m_encodedPointer & singletonFlag()); }
bool hasAnyIncoming() const { return !!m_encodedPointer; }
bool hasSingleton() const { return hasAnyIncoming() && !hasVectorOfCells(); }
JSCell* singleton() const
{
ASSERT(hasSingleton());
return bitwise_cast<JSCell*>(m_encodedPointer & ~singletonFlag());
}
Vector<JSCell*>* vectorOfCells() const
{
ASSERT(hasVectorOfCells());
return bitwise_cast<Vector<JSCell*>*>(m_encodedPointer);
}
// Singleton flag is set: this is a JSCell*.
// Singleton flag not set: this is a pointer to a vector of cells.
uintptr_t m_encodedPointer;
};
} // namespace JSC