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//
// Copyright 2021 The ANGLE Project Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// Spinlock.h:
// Spinlock is a lock that loops actively until it gets the resource.
// Only use it when the lock will be granted in reasonably short time.
#ifndef COMMON_SPINLOCK_H_
#define COMMON_SPINLOCK_H_
#include <atomic>
#if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
extern "C" void _mm_pause();
# pragma intrinsic(_mm_pause)
# define ANGLE_SMT_PAUSE() _mm_pause()
#elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
# define ANGLE_SMT_PAUSE() __asm__ __volatile__("pause;")
#else
# define ANGLE_SMT_PAUSE() static_cast<void>(0)
#endif
namespace angle
{
class Spinlock
{
public:
Spinlock() noexcept;
bool try_lock() noexcept;
void lock() noexcept;
void unlock() noexcept;
private:
std::atomic_bool mLock;
};
inline Spinlock::Spinlock() noexcept : mLock(false) {}
inline bool Spinlock::try_lock() noexcept
{
// Relaxed check first to prevent unnecessary cache misses.
return !mLock.load(std::memory_order_relaxed) &&
!mLock.exchange(true, std::memory_order_acquire);
}
inline void Spinlock::lock() noexcept
{
while (mLock.exchange(true, std::memory_order_acquire))
{
// Relaxed wait to prevent unnecessary cache misses.
while (mLock.load(std::memory_order_relaxed))
{
// Optimization for simultaneous multithreading.
ANGLE_SMT_PAUSE();
}
}
}
inline void Spinlock::unlock() noexcept
{
mLock.store(false, std::memory_order_release);
}
} // namespace angle
#endif // COMMON_SPINLOCK_H_