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| 1 /* |
| 2 * Copyright 2015 Google Inc. |
| 3 * |
| 4 * Use of this source code is governed by a BSD-style license that can be |
| 5 * found in the LICENSE file. |
| 6 */ |
| 7 |
| 8 #ifndef SkSharedLock_DEFINED |
| 9 #define SkSharedLock_DEFINED |
| 10 |
| 11 #include "SkAtomics.h" |
| 12 #include "SkSemaphore.h" |
| 13 #include "SkTypes.h" |
| 14 |
| 15 // This is a shared lock implementation similar to pthreads rwlocks. This implem
entation is |
| 16 // cribbed from Preshing's article: |
| 17 // http://preshing.com/20150316/semaphores-are-surprisingly-versatile/ |
| 18 // |
| 19 // This lock does not obey strict queue ordering. It will always alternate betwe
en readers and |
| 20 // a single writer. |
| 21 class SkSharedMutex { |
| 22 public: |
| 23 SkSharedMutex(); |
| 24 |
| 25 // Acquire lock for exclusive use. |
| 26 void acquire(); |
| 27 |
| 28 // Release lock for exclusive use. |
| 29 void release(); |
| 30 |
| 31 // Acquire lock for shared use. |
| 32 void acquireShared(); |
| 33 |
| 34 // Release lock for shared use. |
| 35 void releaseShared(); |
| 36 |
| 37 private: |
| 38 SkAtomic<int32_t> fQueueCounts; |
| 39 SkSemaphore fSharedQueue; |
| 40 SkSemaphore fExclusiveQueue; |
| 41 }; |
| 42 |
| 43 #endif // SkSharedLock_DEFINED |
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