diff options
Diffstat (limited to 'third_party/base/allocator/partition_allocator/spin_lock.h')
-rw-r--r-- | third_party/base/allocator/partition_allocator/spin_lock.h | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/third_party/base/allocator/partition_allocator/spin_lock.h b/third_party/base/allocator/partition_allocator/spin_lock.h new file mode 100644 index 0000000000..7a42a29c4e --- /dev/null +++ b/third_party/base/allocator/partition_allocator/spin_lock.h @@ -0,0 +1,54 @@ +// Copyright (c) 2013 The Chromium Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +#ifndef BASE_ALLOCATOR_PARTITION_ALLOCATOR_SPIN_LOCK_H +#define BASE_ALLOCATOR_PARTITION_ALLOCATOR_SPIN_LOCK_H + +#include <atomic> +#include <memory> +#include <mutex> + +#include "third_party/base/base_export.h" +#include "third_party/base/compiler_specific.h" + +// Spinlock is a simple spinlock class based on the standard CPU primitive of +// atomic increment and decrement of an int at a given memory address. These are +// intended only for very short duration locks and assume a system with multiple +// cores. For any potentially longer wait you should use a real lock, such as +// |base::Lock|. +// +// |SpinLock|s MUST be globals. Using them as (e.g.) struct/class members will +// result in an uninitialized lock, which is dangerously incorrect. + +namespace pdfium { +namespace base { +namespace subtle { + +class SpinLock { + public: + using Guard = std::lock_guard<SpinLock>; + + ALWAYS_INLINE void lock() { + static_assert(sizeof(lock_) == sizeof(int), + "int and lock_ are different sizes"); + if (LIKELY(!lock_.exchange(true, std::memory_order_acquire))) + return; + LockSlow(); + } + + ALWAYS_INLINE void unlock() { lock_.store(false, std::memory_order_release); } + + private: + // This is called if the initial attempt to acquire the lock fails. It's + // slower, but has a much better scheduling and power consumption behavior. + BASE_EXPORT void LockSlow(); + + std::atomic_int lock_; +}; + +} // namespace subtle +} // namespace base +} // namespace pdfium + +#endif // BASE_ALLOCATOR_PARTITION_ALLOCATOR_SPIN_LOCK_H |