为什么std :: timed_mutex :: try_lock_for不起作用？ [英] Why does std::timed_mutex::try_lock_for not work?

问题描述

我使用gcc-4.8.1（configure：./configure --prefix = / usr / local）在Ubuntu 12.04中编译以下代码，但是当我运行它时，它没有用。并没有停止等待互斥体。它返回false，并输出 Hello world！。

命令：g ++ -std = c ++ 11 main.cpp -omain -pthread

当我使用gcc-4.6（apt-get install g ++）进行编译时，它运行良好。该程序等待了大约十秒钟，并输出了 Hello world！。

  #include< thread> ; 
 #include< iostream> 
 #include< chrono> 
 #include< mutex> 
 
 std :: timed_mutex test_mutex; 
 
 void f（）
 {
 test_mutex.try_lock_for（std :: chrono :: seconds（10））; 
 std :: cout<<  hello world\n； 
} 
 
 int main（）
 {
 std :: lock_guard< std :: timed_mutex> l（test_mutex）; 
 std :: thread t（f）; 
 t.join（）; 
返回0； 
} 
  

解决方案

如果我没记错的话，那就是 Bug 54562 -mutex和条件变量计时器。 / p>

还提到了该错误的原因：

这是因为它使用了CLOCK_MONOTONIC时钟（如果在
平台上可用）来计算它需要返回的绝对时间，
是不正确的，因为POSIX pthread_mutex_timedlock（）调用使用
的CLOCK_REALTIME时钟，然后在在我的平台上，单调时钟比实时时钟落后
。

但是，这并不能解释为什么您看到了在 gcc-4.6 上的正确行为。也许未启用 _GLIBCXX_USE_CLOCK_MONOTONIC ？

I used gcc-4.8.1(configure: ./configure --prefix=/usr/local) to compile following code in Ubuntu 12.04, but when I ran it, it didn't work. it didn't stop to wait the mutex. It returned false, and outputed "Hello world!"

command: g++ -std=c++11 main.cpp -omain -pthread

When I used gcc-4.6(apt-get install g++) to compile it, it worked well. The program waited about ten seconds, and outputed "Hello world!"

#include <thread>
#include <iostream>
#include <chrono>
#include <mutex>

std::timed_mutex test_mutex;

void f()
{
    test_mutex.try_lock_for(std::chrono::seconds(10));
    std::cout << "hello world\n";
}

int main()
{
    std::lock_guard<std::timed_mutex> l(test_mutex);
    std::thread t(f);
    t.join();
      return 0;
}

解决方案

If I am not mistaken, that is Bug 54562 -mutex and condition variable timers.

The reason for the bug is also mentioned:

This is because it uses the CLOCK_MONOTONIC clock (if available on the platform) to calculate the absolute time when it needs to return, which is incorrect as the POSIX pthread_mutex_timedlock() call uses the CLOCK_REALTIME clock, and on my platform the monotonic clock is way behind the real time clock.

However, this doesn't explain why you see the correct behavior on gcc-4.6 though. Perhaps _GLIBCXX_USE_CLOCK_MONOTONIC is not enabled?

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