1 // Copyright (c) 2013 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef THIRD_PARTY_BASE_ALLOCATOR_PARTITION_ALLOCATOR_SPIN_LOCK_H_ 6 #define THIRD_PARTY_BASE_ALLOCATOR_PARTITION_ALLOCATOR_SPIN_LOCK_H_ 7 8 #include <atomic> 9 #include <memory> 10 #include <mutex> 11 12 #include "third_party/base/base_export.h" 13 #include "third_party/base/compiler_specific.h" 14 15 // Spinlock is a simple spinlock class based on the standard CPU primitive of 16 // atomic increment and decrement of an int at a given memory address. These are 17 // intended only for very short duration locks and assume a system with multiple 18 // cores. For any potentially longer wait you should use a real lock, such as 19 // |base::Lock|. 20 namespace pdfium { 21 namespace base { 22 namespace subtle { 23 24 class BASE_EXPORT SpinLock { 25 public: 26 constexpr SpinLock() = default; 27 ~SpinLock() = default; 28 using Guard = std::lock_guard<SpinLock>; 29 lock()30 ALWAYS_INLINE void lock() { 31 static_assert(sizeof(lock_) == sizeof(int), 32 "int and lock_ are different sizes"); 33 if (LIKELY(!lock_.exchange(true, std::memory_order_acquire))) 34 return; 35 LockSlow(); 36 } 37 unlock()38 ALWAYS_INLINE void unlock() { lock_.store(false, std::memory_order_release); } 39 40 private: 41 // This is called if the initial attempt to acquire the lock fails. It's 42 // slower, but has a much better scheduling and power consumption behavior. 43 void LockSlow(); 44 45 std::atomic_int lock_{0}; 46 }; 47 48 } // namespace subtle 49 } // namespace base 50 } // namespace pdfium 51 52 #endif // THIRD_PARTY_BASE_ALLOCATOR_PARTITION_ALLOCATOR_SPIN_LOCK_H_ 53