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/*
* Copyright (C) 2009 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
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND 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 THE COPYRIGHT
* OWNER 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.
*/
#ifndef CrossThreadRefCounted_h
#define CrossThreadRefCounted_h
#include <wtf/Noncopyable.h>
#include <wtf/PassRefPtr.h>
#include <wtf/RefCounted.h>
#include <wtf/Threading.h>
namespace WTF {
// Used to allowing sharing data across classes and threads (like ThreadedSafeShared).
//
// Why not just use ThreadSafeShared?
// ThreadSafeShared can have a significant perf impact when used in low level classes
// (like UString) that get ref/deref'ed a lot. This class has the benefit of doing fast ref
// counts like RefPtr whenever possible, but it has the downside that you need to copy it
// to use it on another thread.
//
// Is this class threadsafe?
// While each instance of the class is not threadsafe, the copied instance is threadsafe
// with respect to the original and any other copies. The underlying m_data is jointly
// owned by the original instance and all copies.
template<class T>
class CrossThreadRefCounted : public Noncopyable {
public:
static PassRefPtr<CrossThreadRefCounted<T> > create(T* data)
{
return adoptRef(new CrossThreadRefCounted<T>(data, 0));
}
// Used to make an instance that can be used on another thread.
PassRefPtr<CrossThreadRefCounted<T> > crossThreadCopy();
void ref();
void deref();
T* release();
bool isShared() const
{
return !m_refCounter.hasOneRef() || (m_threadSafeRefCounter && !m_threadSafeRefCounter->hasOneRef());
}
private:
CrossThreadRefCounted(T* data, ThreadSafeSharedBase* threadedCounter)
: m_threadSafeRefCounter(threadedCounter)
, m_data(data)
#ifndef NDEBUG
, m_threadId(0)
#endif
{
}
~CrossThreadRefCounted()
{
if (!m_threadSafeRefCounter)
delete m_data;
}
void threadSafeDeref();
#ifndef NDEBUG
bool isOwnedByCurrentThread() const { return !m_threadId || m_threadId == currentThread(); }
#endif
RefCountedBase m_refCounter;
ThreadSafeSharedBase* m_threadSafeRefCounter;
T* m_data;
#ifndef NDEBUG
ThreadIdentifier m_threadId;
#endif
};
template<class T>
void CrossThreadRefCounted<T>::ref()
{
ASSERT(isOwnedByCurrentThread());
m_refCounter.ref();
#ifndef NDEBUG
// Store the threadId as soon as the ref count gets to 2.
// The class gets created with a ref count of 1 and then passed
// to another thread where to ref count get increased. This
// is a heuristic but it seems to always work and has helped
// find some bugs.
if (!m_threadId && m_refCounter.refCount() == 2)
m_threadId = currentThread();
#endif
}
template<class T>
void CrossThreadRefCounted<T>::deref()
{
ASSERT(isOwnedByCurrentThread());
if (m_refCounter.derefBase()) {
threadSafeDeref();
delete this;
} else {
#ifndef NDEBUG
// Clear the threadId when the ref goes to 1 because it
// is safe to be passed to another thread at this point.
if (m_threadId && m_refCounter.refCount() == 1)
m_threadId = 0;
#endif
}
}
template<class T>
T* CrossThreadRefCounted<T>::release()
{
ASSERT(!isShared());
T* data = m_data;
m_data = 0;
return data;
}
template<class T>
PassRefPtr<CrossThreadRefCounted<T> > CrossThreadRefCounted<T>::crossThreadCopy()
{
ASSERT(isOwnedByCurrentThread());
if (m_threadSafeRefCounter)
m_threadSafeRefCounter->ref();
else
m_threadSafeRefCounter = new ThreadSafeSharedBase(2);
return adoptRef(new CrossThreadRefCounted<T>(m_data, m_threadSafeRefCounter));
}
template<class T>
void CrossThreadRefCounted<T>::threadSafeDeref()
{
if (m_threadSafeRefCounter && m_threadSafeRefCounter->derefBase()) {
delete m_threadSafeRefCounter;
m_threadSafeRefCounter = 0;
}
}
} // namespace WTF
using WTF::CrossThreadRefCounted;
#endif // CrossThreadRefCounted_h
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