那么pthread_cond_timedwait立即返回

问题描述

我有一个奇怪的问题。我有以下的code：

I'm having a strange problem. I have the following code:

    dbg("condwait: timeout = %d, %d\n",
        abs_timeout->tv_sec, abs_timeout->tv_nsec);
    ret = pthread_cond_timedwait( &q->q_cond, &q->q_mtx, abs_timeout );
    if (ret == ETIMEDOUT)
    {
      dbg("cond timed out\n");
      return -ETIMEDOUT;
    }

DBG 要求 gettimeofday的每一行和prepends前的时间线。它导致的输出如下：

dbg calls gettimeofday before every line and prepends the line with the time. It results in the following output:

    7.991151: condwait: timeout = 5, 705032704
    7.991158: cond timed out

正如你所看到的，只有7微秒两调试线之间传递，但那么pthread_cond_timedwait 返回 ETIMEDOUT 。这怎么可能发生？我甚至尝试初始化COND变量时，时钟设置别的东西：

As you can see, only 7 microseconds passed in between the two debug lines, yet pthread_cond_timedwait returned ETIMEDOUT. How can this happen? I even tried setting the clock to something else when initializing the cond variable:

int ret;
ret = pthread_condattr_init(&attributes);
if (ret != 0) printf("CONDATTR INIT FAILED: %d\n", ret);
ret = pthread_condattr_setclock(&attributes, CLOCK_REALTIME);
if (ret != 0) printf("SETCLOCK FAILED: %d\n", ret);
ret = pthread_cond_init( &q->q_cond, &attributes );
if (ret != 0) printf("COND INIT FAILED: %d\n", ret);

（没有任何错误信息被打印出来）。我想这两个 CLOCK_REALTIME 和 CLOCK_MONOTONIC 。

这code是一个阻塞队列的一部分。我需要的功能，例如，如果没有获取在5秒钟内把这个队列，别的事情发生。互斥和COND都被初始化，因为阻塞队列，如果我不使用正常工作那么pthread_cond_timedwait 。

This code is part of a blocking queue. I need functionality such that if nothing gets put on this queue in 5 seconds, something else happens. The mutex and the cond are both initialized, as the blocking queue works fine if I don't use pthread_cond_timedwait.

推荐答案

那么pthread_cond_timedwait需要一个绝对时间，而不是一个相对时间。你需要让你的等待时间绝对加入到当前的时间，你的超时值。

pthread_cond_timedwait takes an absolute time, not a relative time. You need to make your wait time absolute by adding to the current time to your timeout value.

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