[英]Efficiently wait for a flag state change without blocking resources?
Thread to wait infinitely in a loop until a flag state change, then call function. 线程无限循环地等待直到标志状态改变,然后调用函数。
pseudo code illustration: 伪代码插图:
while (true)
{
while (!flag)
{
sleep(1);
}
clean_upfunction();
}
Currently : 目前 :
No: 没有:
Question: 题:
For Windows (which you have this tagged for), you want to look at WaitForSingleObject . 对于Windows(已对此进行了标记),您需要查看WaitForSingleObject 。 Use a Windows Event (with CreateEvent), then wait on it;
使用Windows事件(带有CreateEvent),然后等待它; the other thread should call SetEvent.
另一个线程应调用SetEvent。 All native Windows, no MFC or anything else required.
所有本机Windows,不需要MFC或其他任何东西。
If you're not on Windows, and are instead on a POSIXish box, pthread_cond_wait
is the best match: 如果您不在Windows上,而是在POSIXish框上,则
pthread_cond_wait
是最佳匹配:
/* signaler */
pthread_mutex_lock(mutex);
flag = true;
pthread_cond_signal(cond);
pthread_mutex_unlock(mutex);
/* waiter */
pthread_mutex_lock(mutex);
do {
pthread_cond_wait(cond, mutex);
} while (!flag);
pthread_mutex_unlock(mutex);
The classic self-pipe trick is easier and cooler though :) Works on systems without pthreads
too. 经典的自管道技巧虽然更容易也更酷:)也可以在没有
pthreads
系统上使用。
/* setup */
int pipefd[2];
if (pipe(pipefd) < 0) {
perror("pipe failed");
exit(-1);
}
/* signaler */
char byte = 0;
write(pipefd[0], &byte, 1); // omitting error handling for brevity
/* waiter */
char byte;
read(pipefd[1], &byte, 1); // omitting error handling for brevity
The waiter will block on the read
(you don't set O_NONBLOCK
) until interrupted (which is why you should have error handling) or the signaler writes a byte. 服务员将阻塞
read
(您不设置O_NONBLOCK
),直到被中断(这就是您应该进行错误处理的原因)或发信号器写入一个字节为止。
Take a look at condition_variable in Boost.Thread. 看一下Boost.Thread中的condition_variable。
http://www.boost.org/doc/libs/1_37_0/doc/html/thread/synchronization.html#thread.synchronization.condvar_ref http://www.boost.org/doc/libs/1_37_0/doc/html/thread/synchronization.html#thread.synchronization.condvar_ref
It is portable, easier to use than the platform-specific options. 它是便携式的,比特定于平台的选件更易于使用。 Moreover, IIUC, the upcoming C++0x std::condition_variable was modeled after it.
而且,IIUC是即将建模的即将发布的C ++ 0x std :: condition_variable。
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