boost信号量 boost::interprocess::interprocess

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。

1 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.

 1 inline bool interprocess_semaphore::timed_wait(const boost::posix_time::ptime &abs_time)
 2 {
 3    if(abs_time == boost::posix_time::pos_infin){
 4       this->wait();
 5       return true;
 6    }
 7    //Obtain current count and target time
 8    boost::posix_time::ptime now(microsec_clock::universal_time());
 9    if(now >= abs_time)
10       return false;
11 
12    do{
13       if(this->try_wait()){
14          break;
15       }
16       now = microsec_clock::universal_time();
17 
18       if(now >= abs_time){
19          return this->try_wait();
20       }
21       // relinquish current time slice
22       detail::thread_yield();
23    }while (true);
24    return true;
25 }

下面举个栗子

 1 #include <boost/interprocess/sync/interprocess_semaphore.hpp>
 2 #include <boost/thread.hpp>
 3 #include <boost/bind.hpp>
 4 #include <boost/date_time/posix_time/posix_time.hpp> 
 5 #include <iostream>
 6 using namespace std;
 7 boost::interprocess::interprocess_semaphore m_semaphore(1);
 8 void test(int i)
 9 {
10     while(true)
11     {
12         if(m_semaphore.try_wait())
13         {
14             printf("%d
",i);
15             m_semaphore.post();
16             
17         }
18         boost::this_thread::sleep(boost::posix_time::seconds(2));
19 
20     }
21 }
22 using namespace boost::posix_time;
23 int main()
24 {
25     boost::thread thread1(boost::bind(&test,1));
26     boost::thread thread2(boost::bind(&test,2));
27     getchar();
28 
29 }