semaphore.hh

Go to the documentation of this file.

/*
 * Scroom - Generic viewer for 2D data
 * Copyright (C) 2009-2022 Kees-Jan Dijkzeul
 *
 * SPDX-License-Identifier: LGPL-2.1
 */
 
#pragma once
 
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/thread.hpp>
 
namespace Scroom
{
  class Semaphore
  {
  private:
    unsigned int              count;
    boost::condition_variable cond;
    boost::mutex              mut;
 
  public:
    explicit Semaphore(unsigned int count = 0);
    void P();
    void V();
 
    template <typename duration_type>
    bool P(duration_type const& rel_time);
 
    bool try_P();
  };
 
  inline Semaphore::Semaphore(unsigned int count_)
    : count(count_)
  {
  }
 
  inline void Semaphore::P()
  {
    boost::mutex::scoped_lock lock(mut);
    while(count == 0)
    {
      cond.wait(lock);
    }
    count--;
  }
 
  inline bool Semaphore::try_P()
  {
    boost::mutex::scoped_lock const lock(mut);
    if(count > 0)
    {
      count--;
      return true;
    }
 
    return false;
  }
 
  template <typename duration_type>
  inline bool Semaphore::P(duration_type const& rel_time)
  {
    boost::posix_time::ptime const timeout = boost::posix_time::second_clock::universal_time() + rel_time;
 
    boost::mutex::scoped_lock lock(mut);
    while(count == 0)
    {
      if(!cond.timed_wait(lock, timeout))
      {
        return false;
      }
    }
    count--;
    return true;
  }
 
  inline void Semaphore::V()
  {
    boost::mutex::scoped_lock const lock(mut);
    count++;
    cond.notify_one();
  }
} // namespace Scroom