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#pragma once
#include "platform.h"
#include "spin_wait.h"
#include <atomic>
class TSpinLockBase {
protected:
TSpinLockBase() = default;
// These were unearthed in IGNIETFERRO-1105
// Need to get rid of them separately
TSpinLockBase(const TSpinLockBase& other)
: Val_(other.Val_.load())
{
}
TSpinLockBase& operator=(const TSpinLockBase& other)
{
Val_.store(other.Val_);
return *this;
}
public:
inline bool IsLocked() const noexcept {
return Val_.load();
}
inline bool TryAcquire() noexcept {
intptr_t zero = 0;
return Val_.compare_exchange_strong(zero, 1);
}
inline bool try_lock() noexcept {
return TryAcquire();
}
protected:
std::atomic<intptr_t> Val_{0};
};
static inline void SpinLockPause() {
#if defined(__GNUC__)
#if defined(_i386_) || defined(_x86_64_)
__asm __volatile("pause");
#elif defined(_arm64_)
__asm __volatile("yield" ::
: "memory");
#endif
#endif
}
/*
* You should almost always use TAdaptiveLock instead of TSpinLock
*/
class TSpinLock: public TSpinLockBase {
public:
using TSpinLockBase::TSpinLockBase;
inline void Release() noexcept {
Val_.store(0, std::memory_order_release);
}
inline void Acquire() noexcept {
intptr_t zero = 0;
if (Val_.compare_exchange_strong(zero, 1)) {
return;
}
do {
SpinLockPause();
zero = 0;
} while (Val_.load(std::memory_order_acquire) != 0 ||
!Val_.compare_exchange_strong(zero, 1));
}
inline void unlock() noexcept {
Release();
}
inline void lock() noexcept {
Acquire();
}
};
/**
* TAdaptiveLock almost always should be used instead of TSpinLock.
* It also should be used instead of TMutex for short-term locks.
* This usually means that the locked code should not use syscalls,
* since almost every syscall:
* - might run unpredictably long and the waiting thread will waste a lot of CPU
* - takes considerable amount of time, so you should not care about the mutex performance
*/
class TAdaptiveLock: public TSpinLockBase {
public:
using TSpinLockBase::TSpinLockBase;
void Release() noexcept {
Val_.store(0, std::memory_order_release);
}
void Acquire() noexcept {
intptr_t zero = 0;
if (Val_.compare_exchange_strong(zero, 1)) {
return;
}
TSpinWait sw;
for (;;) {
zero = 0;
if (Val_.load(std::memory_order_acquire) == 0 &&
Val_.compare_exchange_strong(zero, 1)) {
break;
}
sw.Sleep();
}
}
inline void unlock() noexcept {
Release();
}
inline void lock() noexcept {
Acquire();
}
};
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