#include <boost/thread/condition_variable.hpp>

#include <boost/thread/mutex.hpp>    

#include <boost/thread/lock_types.hpp>

#include <boost/thread.hpp> 

 

class semaphore

{

    unsigned int count_;

    boost::mutex mutex_;

    boost::condition_variable condition_;

 

public:

    explicit semaphore(unsigned int initial) : count_(initial){}

 

    void signal()

    {

        {

            boost::lock_guard<boost::mutex> lock(mutex_);

            ++count_;

        }

        condition_.notify_one(); 

    }

 

    void wait() 

    {

        boost::unique_lock<boost::mutex> lock(mutex_);

        while (count_ == 0)

        {

             condition_.wait(lock);

        }

        --count_;

    }

};