如果我在进行timed_wait持续时间时系统时间发生了变化，该怎么办? [英] What if the system time changes while I'm doing timed_wait with a duration?

问题描述

在持续时间为 boost :: condition_variable 的持续时间上使用 timed_wait 时，即使用户(或ntp)更改了系统，等待条件也会在持续时间后超时时间?

When using timed_wait on a boost::condition_variable with a duration, will the wait condition time out after the duration even if the user (or ntp) changes the system time?

例如，

boost::posix_time::time_duration wait_duration(0, 0, 1, 0);  // 1 sec
// ** System time jumps back 15 minutes here. **
if( !signal.timed_wait(lock, wait_duration) )
{
    // Does this condition happen 1 second later, or about 15 minutes later?
}

推荐答案

截至撰写之日(2013年11月)，如果在等待升压条件变量时挂钟时间发生了变化，您只会得到结果不好.

As of the date of writing (Nov 2013), if the wall-clock time changes while you're waiting on a boost condition variable, you simply will get bad results.

如果您不必使用加速功能，则可以使用所谓的单调时钟".由于单调时钟不受挂钟时间更改的影响，因此它不会受到您描述的问题的影响.您可以使用pthreads API安全地等待5秒钟，如下所示:

If you don't have to use boost, you can use what is called the "monotonic clock." Since the monotonic clock is unaffected by wall-clock time changes, it is not vulnerable to the problem you described. You can safely wait 5 seconds using the pthreads API using something like this:

pthread_condattr_t attr;
pthread_cond_t cond;
struct timespec ts;

pthread_condattr_init(&attr);
pthread_condattr_setclock(&attr, CLOCK_MONOTONIC);
pthread_cond_init(&cond, &attr);
pthread_condattr_destroy(&attr);
clock_gettime(CLOCK_MONOTONIC, &ts);
ts.tv_sec += 5;
pthreead_cond_timedwait(&cond, &mutex, &ts);

您可以检查boost :: condition_variable的实现.也许他们有一天会解决这个问题.实现在这里: http://svn.boost.org/svn/boost/trunk/boost/thread/pthread/condition_variable.hpp

You can check the implementation of boost::condition_variable. Maybe they will fix this some day. The implementation is here: http://svn.boost.org/svn/boost/trunk/boost/thread/pthread/condition_variable.hpp

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