Re: [Boost-users] condition_variable

Subject: Re: [Boost-users] condition_variable
From: Alessandro Bellina (abellina_at_[hidden])
Date: 2009-12-11 07:03:19

Spurious wake ups?

Thanks for posting your example. I don't really know why we need to set
"some_event_occurred". Is this the recommended usage?
Other than your first iteration (where you need the flag, but that is
because you are using a do/while as opposed to a while loop), are we
supposed to get spurious wake ups (i.e. will timed_wait return true even if
we didn't call notify_one)?

Alessandro

On Thu, Dec 10, 2009 at 4:11 PM, Adam Szeliga
<aszeliga.xsoftware_at_[hidden]>wrote:

> This is scheme which I often use:
>
> // Common for both threads
> boost::mutex mutex;
> boost::condition condition;
>
> // Thread1:
>
> boost::xtime waitingTime(set value of waiting time)
> {
>
>    boost::mutex::scoped_lock lock(mutex)
>     do
>    {
>       if (some_event occurred)
>       {
>            do something after received event
>            return; // exit point after receive event
>       }
>    } while (condition.timed_wait(lock, waitingTime));
>    do something after timeout occurred  // exit point after timeout
> }
>
>
> //Thread2
>
> {
>    boost::mutex::scoped_lock lock(mutex);
>     set some event which is been waiting thread1
>    condition.notify_one();
> }
>
> Maybe will be useful for you.
> Adam
>
> Nikolai N Fetissov wrote:
> >> Thanks Nikolai,
> >> That explains why the second thread can lock that mutex. From what you
> are
> >> saying then, the sleeping thread will wake up and reacquire the lock
> after
> >> notify is called. So the thread that calls notify should not hold that
> >> lock
> >> when this happens or you could have deadlock right?.
> >>
> >>
> >
> > Alessandro,
> >
> > The thread calling the 'notify' can, but does not have to, hold
> > a mutex at the time. In theory all the notify() function does is
> > mark the thread sleeping on the condition as runnable. There's
> > no deadlock here. Also google for 'spurious wakeup' to get a firm
> > hold on mutex/cv concepts.
> >
> > Cheers,
> > --
> >  Nikolai
> >
> > _______________________________________________
> > Boost-users mailing list
> > Boost-users_at_[hidden]
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> >
>
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