mutex is used to serialize access to a shared resource among competing threads.
condition variable is used to notify a state change of a resource to the interested thread.
In case of condition variable there is provision to explicitly notify a single thread(pthread_cond_signal) or all the threads waiting on a condition (or a state change) (pthread_cond_broadcast)
Question was on pthread_mutex_unlock() that whether this function invocation will trigger the movement of all the threads in the wait queue to the ready queue.
If all the threads are of equal priority, then the first thread waiting for the lock will be put to READY queue.
If there are variable priority threads waiting for the lock, then the thread with highest priority would be woken up
Regards,
Prabhunath G
Linux Trainer
Bangalore
Prabhunath G
Linux Trainer
Bangalore
On Tue, Mar 5, 2013 at 3:35 PM, ishare <june.tune.sea@xxxxxxxxx> wrote:
On Tue, Mar 05, 2013 at 01:39:54PM +0530, Mandeep Sandhu wrote:the threads waiting on sockets will be waked up by net event.
> On Tue, Mar 5, 2013 at 11:32 AM, <Valdis.Kletnieks@xxxxxx> wrote:
> > On Tue, 05 Mar 2013 11:02:45 +0530, Mandeep Sandhu said:
> >
> >> next schedule. I think the waiting threads (processes) will moved from
> >> the wait queue to the run queue from where they will be scheduled to
> >> run.
> >
> > For bonus points, read source code and/or comments and figure out what
> > Linux does to prevent the 'thundering herd' problem (consider 100 threads
> > all waiting on the same mutex - if you blindly wake all 100 up, you'll schedule
> > them all, the first will find the mutex available and then re-take it, and
> > then the next 99 will get run only to find it contended and go back to
> > sleep. So figure out what Linux does in that case. :)
>
> Googling around, I found the 'thundering herd' being mentioned in
> relation to threads waiting on sockets using the accept() sys call.
> Are wait's on mutex's also plagued by the same issue? I guess it is,
> though what sys call would be used in this case?
similarly,the waiters on mutex's can be wake up by signal.I guess it is pthread_cont_signal
>
> Thanks,
> -mandeep
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