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/*
* Copyright 2015 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkSharedLock_DEFINED
#define SkSharedLock_DEFINED
#include "SkAtomics.h"
#include "SkSemaphore.h"
#include "SkTypes.h"
// This is a shared lock implementation similar to pthreads rwlocks. This implementation is
// cribbed from Preshing's article:
// http://preshing.com/20150316/semaphores-are-surprisingly-versatile/
//
// This lock does not obey strict queue ordering. It will always alternate between readers and
// a single writer.
class SkSharedMutex {
public:
SkSharedMutex();
~SkSharedMutex();
// Acquire lock for exclusive use.
void acquire();
// Release lock for exclusive use.
void release();
// Fail if exclusive is not held.
#ifdef SK_DEBUG
void assertHeld() const;
#else
void assertHeld() const {}
#endif
// Acquire lock for shared use.
void acquireShared();
// Release lock for shared use.
void releaseShared();
// Fail if shared lock not held.
#ifdef SK_DEBUG
void assertHeldShared() const;
#else
void assertHeldShared() const {}
#endif
private:
SkAtomic<int32_t> fQueueCounts;
SkSemaphore fSharedQueue;
SkSemaphore fExclusiveQueue;
};
#endif // SkSharedLock_DEFINED
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