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 SkSpinlock_DEFINED 9 #define SkSpinlock_DEFINED 10 11 #include "include/private/base/SkAPI.h" 12 #include "include/private/base/SkThreadAnnotations.h" 13 14 #include <atomic> 15 16 class SK_CAPABILITY("mutex") SkSpinlock { 17 public: 18 constexpr SkSpinlock() = default; 19 acquire()20 void acquire() SK_ACQUIRE() { 21 // To act as a mutex, we need an acquire barrier when we acquire the lock. 22 if (fLocked.exchange(true, std::memory_order_acquire)) { 23 // Lock was contended. Fall back to an out-of-line spin loop. 24 this->contendedAcquire(); 25 } 26 } 27 28 // Acquire the lock or fail (quickly). Lets the caller decide to do something other than wait. tryAcquire()29 bool tryAcquire() SK_TRY_ACQUIRE(true) { 30 // To act as a mutex, we need an acquire barrier when we acquire the lock. 31 if (fLocked.exchange(true, std::memory_order_acquire)) { 32 // Lock was contended. Let the caller decide what to do. 33 return false; 34 } 35 return true; 36 } 37 release()38 void release() SK_RELEASE_CAPABILITY() { 39 // To act as a mutex, we need a release barrier when we release the lock. 40 fLocked.store(false, std::memory_order_release); 41 } 42 43 private: 44 SK_API void contendedAcquire(); 45 46 std::atomic<bool> fLocked{false}; 47 }; 48 49 class SK_SCOPED_CAPABILITY SkAutoSpinlock { 50 public: SkAutoSpinlock(SkSpinlock & mutex)51 SkAutoSpinlock(SkSpinlock& mutex) SK_ACQUIRE(mutex) : fSpinlock(mutex) { fSpinlock.acquire(); } SK_RELEASE_CAPABILITY()52 ~SkAutoSpinlock() SK_RELEASE_CAPABILITY() { fSpinlock.release(); } 53 54 private: 55 SkSpinlock& fSpinlock; 56 }; 57 58 #endif//SkSpinlock_DEFINED 59