herb | c782b2a | 2015-06-29 13:46:55 -0700 | [diff] [blame^] | 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 implementation 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 between 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 |