boost信号量 boost::interprocess::interprocess_semaphore的用法

   使用方法首先给信号量初始化赋值,可以根据需要设定需要的值,之前在写项目的过程中用这个控制下载的线程个数。

boost::interprocess::interprocess_semaphore m_semaphore(0);

    然后就是pv操作了,v操作就只有一个post(),post()一次,信号量加1.p操作有三个,看函数名字都很明显知道是什么意思,

 wait(),try_wait() ,timed_wait(const boost::posix_time::ptime&abs_time).

   这里需要注意的是第三个p操做,对boost也不太熟, 很明显是等待到某一时间点,m_semaphore.timed_wait(boost::posix_time::ptime(second_clock::universal_time()+boost::posix_time::seconds(1))),等待一秒;这个时间是取universal_time,一开始不知道，试了几次不行，后面灵机一动看了下源码，原来如此.

inline bool interprocess_semaphore::timed_wait(const boost::posix_time::ptime &abs_time)
{
   if(abs_time == boost::posix_time::pos_infin){
      this->wait();
      return true;
   }
   //Obtain current count and target time
   boost::posix_time::ptime now(microsec_clock::universal_time());
   if(now >= abs_time)
      return false;

   do{
      if(this->try_wait()){
         break;
      }
      now = microsec_clock::universal_time();

      if(now >= abs_time){
         return this->try_wait();
      }
      // relinquish current time slice
      detail::thread_yield();
   }while (true);
   return true;
}

 下面举个栗子

#include <boost/interprocess/sync/interprocess_semaphore.hpp>
#include <boost/thread.hpp>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time.hpp> 
#include <iostream>
using namespace std;
boost::interprocess::interprocess_semaphore m_semaphore(1);
void test(int i)
{
    while(true)
    {
        if(m_semaphore.try_wait())
        {
            printf("%d
",i);
            m_semaphore.post();
            
        }
        boost::this_thread::sleep(boost::posix_time::seconds(2));

    }
}
using namespace boost::posix_time;
int main()
{
    boost::thread thread1(boost::bind(&test,1));
    boost::thread thread2(boost::bind(&test,2));
    getchar();

}