semaphore_fast.h

#pragma once
 
#include "gaia/config/config.h"
 
#include <atomic>
 
#include "gaia/mt/semaphore.h"
 
namespace gaia {
  namespace mt {
    class GAIA_API SemaphoreFast final {
      Semaphore m_sem;
      std::atomic_int32_t m_cnt;
 
      SemaphoreFast(SemaphoreFast&&) = delete;
      SemaphoreFast(const SemaphoreFast&) = delete;
      SemaphoreFast& operator=(SemaphoreFast&&) = delete;
      SemaphoreFast& operator=(const SemaphoreFast&) = delete;
 
    public:
      explicit SemaphoreFast(int32_t count = 0): m_sem(count), m_cnt(0) {}
      ~SemaphoreFast() = default;
 
      void release(int32_t count = 1) {
        const int32_t prevCount = m_cnt.fetch_add(count, std::memory_order_release);
        int32_t toRelease = -prevCount;
        if (count < toRelease)
          toRelease = count;
 
        if (toRelease > 0)
          m_sem.release(toRelease);
      }
 
      bool wait() {
        const int32_t oldCount = m_cnt.fetch_sub(1, std::memory_order_acquire);
        bool result = true;
        if (oldCount <= 0)
          result = m_sem.wait();
 
        return result;
      }
    };
  } // namespace mt
} // namespace gaia