| /* |
| * 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 "include/core/SkTypes.h" |
| #include "include/private/base/SkMacros.h" |
| #include "include/private/base/SkSemaphore.h" |
| #include "include/private/base/SkThreadAnnotations.h" |
| #include <atomic> |
| |
| #ifdef SK_DEBUG |
| #include "include/private/base/SkMutex.h" |
| #include <memory> |
| #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 SK_CAPABILITY("mutex") SkSharedMutex { |
| public: |
| SkSharedMutex(); |
| ~SkSharedMutex(); |
| // Acquire lock for exclusive use. |
| void acquire() SK_ACQUIRE(); |
| |
| // Release lock for exclusive use. |
| void release() SK_RELEASE_CAPABILITY(); |
| |
| // Fail if exclusive is not held. |
| void assertHeld() const SK_ASSERT_CAPABILITY(this); |
| |
| // Acquire lock for shared use. |
| void acquireShared() SK_ACQUIRE_SHARED(); |
| |
| // Release lock for shared use. |
| void releaseShared() SK_RELEASE_SHARED_CAPABILITY(); |
| |
| // Fail if shared lock not held. |
| void assertHeldShared() const SK_ASSERT_SHARED_CAPABILITY(this); |
| |
| private: |
| #ifdef SK_DEBUG |
| class ThreadIDSet; |
| std::unique_ptr<ThreadIDSet> fCurrentShared; |
| std::unique_ptr<ThreadIDSet> fWaitingExclusive; |
| std::unique_ptr<ThreadIDSet> fWaitingShared; |
| int fSharedQueueSelect{0}; |
| mutable SkMutex fMu; |
| SkSemaphore fSharedQueue[2]; |
| SkSemaphore fExclusiveQueue; |
| #else |
| std::atomic<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 |
| |
| class SK_SCOPED_CAPABILITY SkAutoSharedMutexExclusive { |
| public: |
| explicit SkAutoSharedMutexExclusive(SkSharedMutex& lock) SK_ACQUIRE(lock) |
| : fLock(lock) { |
| lock.acquire(); |
| } |
| ~SkAutoSharedMutexExclusive() SK_RELEASE_CAPABILITY() { fLock.release(); } |
| |
| private: |
| SkSharedMutex& fLock; |
| }; |
| |
| class SK_SCOPED_CAPABILITY SkAutoSharedMutexShared { |
| public: |
| explicit SkAutoSharedMutexShared(SkSharedMutex& lock) SK_ACQUIRE_SHARED(lock) |
| : fLock(lock) { |
| lock.acquireShared(); |
| } |
| |
| // You would think this should be SK_RELEASE_SHARED_CAPABILITY, but SK_SCOPED_CAPABILITY |
| // doesn't fully understand the difference between shared and exclusive. |
| // Please review https://reviews.llvm.org/D52578 for more information. |
| ~SkAutoSharedMutexShared() SK_RELEASE_CAPABILITY() { fLock.releaseShared(); } |
| |
| private: |
| SkSharedMutex& fLock; |
| }; |
| |
| #endif // SkSharedLock_DEFINED |