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/*
* Copyright (C) 2014 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. AND ITS CONTRIBUTORS ``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 ITS 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/Function.h>
#include <wtf/Noncopyable.h>
#include <wtf/RefPtr.h>
#include <wtf/SetForScope.h>
namespace WTF {
enum class RefCounterEvent { Decrement, Increment };
template<typename T>
class RefCounter {
WTF_MAKE_FAST_ALLOCATED;
WTF_MAKE_NONCOPYABLE(RefCounter);
class Count {
WTF_MAKE_NONCOPYABLE(Count);
public:
void ref();
void deref();
void refCounterWasDeleted();
private:
friend class RefCounter;
Count(RefCounter& refCounter)
: m_refCounter(&refCounter)
, m_value(0)
{
}
RefCounter* m_refCounter;
size_t m_value;
bool m_inValueDidChange { false };
};
public:
using Token = RefPtr<Count>;
using ValueChangeFunction = WTF::Function<void (RefCounterEvent)>;
RefCounter(ValueChangeFunction&& = nullptr);
~RefCounter();
Token count() const
{
return m_count;
}
size_t value() const
{
return m_count->m_value;
}
private:
ValueChangeFunction m_valueDidChange;
Count* m_count;
};
template<typename T>
inline void RefCounter<T>::Count::ref()
{
++m_value;
if (m_refCounter && m_refCounter->m_valueDidChange)
m_refCounter->m_valueDidChange(RefCounterEvent::Increment);
}
template<typename T>
inline void RefCounter<T>::Count::deref()
{
// GCC gets confused here, see https://webkit.org/b/239338.
IGNORE_GCC_WARNINGS_BEGIN("use-after-free")
ASSERT(m_value);
--m_value;
if (m_refCounter && m_refCounter->m_valueDidChange) {
SetForScope inCallback(m_inValueDidChange, true);
m_refCounter->m_valueDidChange(RefCounterEvent::Decrement);
}
IGNORE_GCC_WARNINGS_END
// The Count object is kept alive so long as either the RefCounter that created it remains
// allocated, or so long as its reference count is non-zero.
// If the RefCounter has already been deallocted then delete the Count when its reference
// count reaches zero.
if (!m_refCounter && !m_value)
delete this;
}
template<typename T>
inline void RefCounter<T>::Count::refCounterWasDeleted()
{
// The Count object is kept alive so long as either the RefCounter that created it remains
// allocated, or so long as its reference count is non-zero.
// If the reference count of the Count is already zero then delete it now, otherwise
// clear its m_refCounter pointer.
m_refCounter = nullptr;
if (m_inValueDidChange)
return;
if (!m_value)
delete this;
}
template<typename T>
inline RefCounter<T>::RefCounter(ValueChangeFunction&& valueDidChange)
: m_valueDidChange(WTFMove(valueDidChange))
, m_count(new Count(*this))
{
}
template<typename T>
inline RefCounter<T>::~RefCounter()
{
m_count->refCounterWasDeleted();
}
} // namespace WTF
using WTF::RefCounter;
using WTF::RefCounterEvent;
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