Re: [boost] Condition Variables, POSIX signals and system time changes

Subject: Re: [boost] Condition Variables, POSIX signals and system time changes
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2012-01-10 16:38:07

Le 10/01/12 08:35, Johan Borkhuis a écrit :
> I came across the following issue with condition variables. I don't know
> if this is an issue with my application or with Boost condition variables.
>
> First my setup. I am using Linux on an ARM system, running Boost 1.47. My
> application needs accurate timing, and for this I use a POSIX timer using
> SIGRTMIN. This part is not something that I can control, it is an external
> library that implements this. I use condition variables are a timing
> mechanism with in my software.
Do you mean that you are not using Boost.thread here?
> When I use condition variables without the POSIX timer there is no
> problem. The timing continues correctly, even if I change the time forward
> or backward.
>
> When I start the POSIX timer the condition variable does not time-out when
> I change the time backward. It only times out when the original time (plus
> timeout) is reached.
>
> The code I use to create the condition variable:
>
>      boost::mutex m;
>      boost::condition_variable cond;
>      boost::unique_lock<boost::mutex>  lk(m);
>      cond.timed_wait(lk, duration);
>
> I tested this also by extracting the code from Boost and implementing this
> inline. This gave the same results. When I changed the clock of the
> pthread condition variable to monotonic (call to
> pthread_condattr_setclock(&condattr, CLOCK_MONOTONIC)) the result was OK
> again.
What do you changed exactly? Could you post a patch?
> Is this an issue with my implementation, can I change some setting or is
> this a (known) issue with the Boost condition variables?
>
> If people are interested, I do have a small test application that I used
> to test this issue that I can post here. I don't know however what the
> policy is on this list wrt posting of attachments.
>
>

Please, could you post the test that fails and the one that succeeds, it 
will help me a lot.

If you want you can open a Trac ticket and attach the examples and the 
path there.

Best,
Vicente