Re: [Boost-users] boost::interprocess::interprocess_semaphore::timed_wait - how to do a relative wait

Subject: Re: [Boost-users] boost::interprocess::interprocess_semaphore::timed_wait - how to do a relative wait
From: Viatcheslav.Sysoltsev_at_[hidden]
Date: 2011-02-24 05:03:25

On Thu, 17 Feb 2011 16:02:06 +0100, Jean-Sebastien Stoezel  
<js.stoezel_at_[hidden]> wrote:

> Hi:
>
> I won't provide an example, just either do a sleep, or call a timed wait  
> on
> a semaphore, mutex etc... with a long enough timeout (say 60s). While  
> your
> thread is waiting, change the clock of your computer backwards by say 2h.
> Your thread will be waiting 2h instead of 60s.
>

Well, I tried the following test program:

#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/interprocess/sync/interprocess_semaphore.hpp>

int main()
{
     struct timespec td_start,td_end;
     boost::interprocess::interprocess_semaphore sem(0);
     boost::posix_time::ptime  
t(boost::posix_time::microsec_clock::universal_time());
     printf("Start waiting\n");
     clock_gettime(CLOCK_MONOTONIC, &td_start);
     bool ret = sem.timed_wait(t + boost::posix_time::seconds(30));
     clock_gettime(CLOCK_MONOTONIC, &td_end);
     printf("Finished waiting %s, waited %d seconds\n", ret == false ? "due  
to timeout" : "due to some other semaphore event",  
td_end.tv_sec-td_start.tv_sec);
     return 0;
}

compiled with gcc 4.3.2 on SUSE 11.1 (usual x86) against boost 1.45, it  
happens to run just fine:
vsysolts:~/test/boost (1) > g++ -g -O0 -I/home/vsysolts/boost/boost_1_45_0  
-L/home/vsysolts/boost/boost_1_45_0/stage/lib test2.cpp -lboost_date_time  
-lpthread && a.out
Start waiting
Finished waiting due to timeout, waited 30 seconds

I have set the system clock 5 minutes back while it was waiting. It has  
waited for around 30 seconds, definitely not for about 5 minutes.

Btw the native semaphores are not affected by system time on my system too.

So what are you objecting against *exactly*?

-- Slava