Spinlock.h (1806B)
1 // 2 // Copyright 2021 The ANGLE Project Authors. All rights reserved. 3 // Use of this source code is governed by a BSD-style license that can be 4 // found in the LICENSE file. 5 // 6 // Spinlock.h: 7 // Spinlock is a lock that loops actively until it gets the resource. 8 // Only use it when the lock will be granted in reasonably short time. 9 10 #ifndef COMMON_SPINLOCK_H_ 11 #define COMMON_SPINLOCK_H_ 12 13 #include <atomic> 14 15 // TODO(jplate) Add pause for ARM, http://anglebug.com:6067 16 #if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64)) 17 extern "C" void _mm_pause(); 18 # pragma intrinsic(_mm_pause) 19 # define ANGLE_SMT_PAUSE() _mm_pause() 20 #elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__)) 21 # define ANGLE_SMT_PAUSE() __asm__ __volatile__("pause;") 22 #else 23 # define ANGLE_SMT_PAUSE() static_cast<void>(0) 24 #endif 25 26 namespace angle 27 { 28 29 class Spinlock 30 { 31 public: 32 Spinlock() noexcept; 33 34 bool try_lock() noexcept; 35 void lock() noexcept; 36 void unlock() noexcept; 37 38 private: 39 std::atomic_bool mLock; 40 }; 41 42 inline Spinlock::Spinlock() noexcept : mLock(false) {} 43 44 inline bool Spinlock::try_lock() noexcept 45 { 46 // Relaxed check first to prevent unnecessary cache misses. 47 return !mLock.load(std::memory_order_relaxed) && 48 !mLock.exchange(true, std::memory_order_acquire); 49 } 50 51 inline void Spinlock::lock() noexcept 52 { 53 while (mLock.exchange(true, std::memory_order_acquire)) 54 { 55 // Relaxed wait to prevent unnecessary cache misses. 56 while (mLock.load(std::memory_order_relaxed)) 57 { 58 // Optimization for simultaneous multithreading. 59 ANGLE_SMT_PAUSE(); 60 } 61 } 62 } 63 64 inline void Spinlock::unlock() noexcept 65 { 66 mLock.store(false, std::memory_order_release); 67 } 68 69 } // namespace angle 70 71 #endif // COMMON_SPINLOCK_H_