Re: [Boost-users] Boost semaphore with condition variable

22 Nov 2007

      Fabian Sturm  writes:
...
Hi!
I have a quite simple problem, but I still lack a nice implementation in
C++ with boost.
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 ();
Correct way to use condvar is the following:

Thread A:
mutex::scoped_lock lock(mutex);
while (!dataCalculated)
    condvar.wait(lock);

Thread B:
mutex::scoped_lock lock(mutex);
dataCalculated = true;
condvar.notify_one();

Instead of 'while' loop you can use
condition::wait with a predicate:

Thread A:
mutex::scoped_lock lock(mutex);
condvar.wait(lock, var(dataCalculated));

Regards,
Roman Perepelitsa.