spinlock.h

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#ifndef QB_SPINLOCK_H
#define QB_SPINLOCK_H
#include <atomic>
#include <qb/system/timestamp.h>
 
namespace qb::lockfree {

class SpinLock {
public:
    SpinLock() noexcept
        : _lock(false) {}

    SpinLock(const SpinLock &) = delete;

    SpinLock(SpinLock &&) = delete;

    ~SpinLock() = default;

    SpinLock &operator=(const SpinLock &) = delete;

    SpinLock &operator=(SpinLock &&) = delete;

    bool
    locked() noexcept {
        return _lock.load(std::memory_order_acquire);
    }

    bool
    trylock() noexcept {
        return !_lock.exchange(true, std::memory_order_acquire);
    }

    bool
    trylock(int64_t spin) noexcept {
        // Try to acquire spin-lock at least one time
        do {
            if (trylock())
                return true;
        } while (spin-- > 0);
 
        // Failed to acquire spin-lock
        return false;
    }

    bool
    trylock_for(const Timespan &timespan) noexcept {
        // Calculate a finish timestamp
        Timestamp finish = NanoTimestamp() + timespan;
 
        // Try to acquire spin-lock at least one time
        do {
            if (trylock())
                return true;
        } while (NanoTimestamp() < finish);
 
        // Failed to acquire spin-lock
        return false;
    }

    bool
    trylock_until(const UtcTimestamp &timestamp) noexcept {
        return trylock_for(timestamp - UtcTimestamp());
    }

    void
    lock() noexcept {
        while (_lock.exchange(true, std::memory_order_acquire))
            ;
    }

    void
    unlock() noexcept {
        _lock.store(false, std::memory_order_release);
    }
 
private:
    std::atomic<bool> _lock; 
};
 
} // namespace qb::lockfree
 
#endif // QB_SPINLOCK_H