From: Steve Byan (Steve.Byan_at_[hidden])
Date: 2007-11-22 08:48:17
On Nov 21, 2007, at 5:25 PM, Fabian Sturm wrote:
> My problem is, that I have two threads A and B and thread A needs some
> information that B will calculate at runtime. Therefore I need some
> kind
> of synchronization.
>
> So my first attempt was to use a mutex and a condition variable:
>
> Thread A:
>
> boost::thread::mutex::scoped_lock lock ( mMutex );
> mConditionVar.wait ( lock );
>
> Thread B:
>
> mConditionVar.notify_one ();
>
> This works nice as long as thread A already started waiting on the
> condition before thread B finished providing it. Otherwise the notify
> will be lost.
You need to create a shared condition variable, set by thread B and
read by thread A.
Thread A has to wait on the condition variable in a loop, like this:
shared variable:
bool theCondition = false;
Thread A:
{
boost::thread::mutex::scoped_lock lock ( mMutex );
while (!theCondition) {
mConditionVar.wait ( lock );
}
}
Thread B:
{
boost::thread::mutex::scoped_lock lock ( mMutex );
theCondition = true;
mConditionVar.notify_one ();
}
I suggest you take a look at a tutorial text on POSIX threads
(pthreads); it should explain the use of mutexes and condition
variables more thoroughly.
Regards,
-Steve
-- Steve Byan <stevebyan_at_[hidden]> Littleton, MA 01460