| /* |
| * 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" |
| |
| #ifdef SK_DEBUG |
| #include "SkMutex.h" |
| #include "../private/SkUniquePtr.h" |
| #endif // SK_DEBUG |
| |
| // There are two shared lock implementations one debug the other is high performance. They implement |
| // an interface similar to pthread's rwlocks. |
| // This is a shared lock implementation similar to pthreads rwlocks. The high performance |
| // 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. |
| void assertHeld() const; |
| |
| // Acquire lock for shared use. |
| void acquireShared(); |
| |
| // Release lock for shared use. |
| void releaseShared(); |
| |
| // Fail if shared lock not held. |
| void assertHeldShared() const; |
| |
| private: |
| #ifdef SK_DEBUG |
| class ThreadIDSet; |
| skstd::unique_ptr<ThreadIDSet> fCurrentShared; |
| skstd::unique_ptr<ThreadIDSet> fWaitingExclusive; |
| skstd::unique_ptr<ThreadIDSet> fWaitingShared; |
| int fSharedQueueSelect{0}; |
| mutable SkMutex fMu; |
| SkSemaphore fSharedQueue[2]; |
| SkSemaphore fExclusiveQueue; |
| #else |
| SkAtomic<int32_t> fQueueCounts; |
| SkSemaphore fSharedQueue; |
| SkSemaphore fExclusiveQueue; |
| #endif // SK_DEBUG |
| }; |
| |
| #ifndef SK_DEBUG |
| inline void SkSharedMutex::assertHeld() const {}; |
| inline void SkSharedMutex::assertHeldShared() const {}; |
| #endif // SK_DEBUG |
| |
| #endif // SkSharedLock_DEFINED |