latch.hpp

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#ifndef MSTL_CORE_ASYNC_LATCH_HPP__
#define MSTL_CORE_ASYNC_LATCH_HPP__

 
#include "atomic_base.hpp"
MSTL_BEGIN_NAMESPACE__


class latch {
private:
    alignas(alignof(platform_wait_t)) platform_wait_t counter_;   
 
public:
    static constexpr platform_wait_t max() noexcept {
        return numeric_traits<platform_wait_t>::max();
    }

    constexpr explicit latch(const platform_wait_t expected) noexcept
    : counter_(expected) {
        MSTL_CONSTEXPR_ASSERT(expected >= 0);
    }
 
    ~latch() = default;  
    latch(const latch&) = delete;  
    latch& operator =(const latch&) = delete;  

    MSTL_ALWAYS_INLINE void count_down(const platform_wait_t update = 1) {
        auto const old_value = _MSTL atomic_fetch_sub(&counter_, update, memory_order_release);
        if (old_value == update) {
            _MSTL atomic_notify_address(&counter_, true);
        }
    }

    MSTL_ALWAYS_INLINE bool try_wait() const noexcept {
        return _MSTL atomic_load(&counter_, memory_order_acquire) == 0;
    }

    MSTL_ALWAYS_INLINE void wait() const noexcept {
        auto const predicate = [this] { return this->try_wait(); };
        _MSTL atomic_wait_address(&counter_, predicate);
    }

    MSTL_ALWAYS_INLINE void arrive_and_wait(const platform_wait_t update = 1) noexcept {
        count_down(update);
        wait();
    }
};
 // Latches
 
MSTL_END_NAMESPACE__
#endif // MSTL_CORE_ASYNC_LATCH_HPP__