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();

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();
 void test(int i)
 {
     while(true)
     {
         if(m_semaphore.try_wait())
         {
             printf("%d\n",i);
             m_semaphore.post();

         }
         boost::this_thread::sleep(boost::posix_time::seconds());

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

 }