Re: [Boost-Users] Boost.Threads question

From: William E. Kempf (wekempf_at_[hidden])
Date: 2002-12-04 11:04:34

James Zappia said:
> Hi,
>
> I'm a newbie to C++ and Boost and I'm trying to port a threaded C
> program I have to Boost.Threads.  I'm trying to use scoped_try_lock to
> test a lock on mutex and it's not working.  I'm obviously doing
> something wrong but I can't figure it out.  Below is the source code.
> Any help would be greatly appreciated.

How is it not working?  What do you expect to happen?

> SOURCE:
>
> #include <iostream>
> #include <boost/thread/thread.hpp>
> #include <boost/thread/exceptions.hpp>
>
> using namespace std;
>
> boost::try_mutex mutex;
>
> void thread_test( void )
> {
> 	cout << "thread: locking mutex\n";
>
> 	{
> 		boost::try_mutex::scoped_try_lock lock(mutex);
> 		cout << "thread: sleeping for 10 seconds\n";
> 		sleep(10);
> 	}
>
> 	cout << "thread: unlocked mutex - goodbye!\n";
>
> 	return;
> }
>
> int main( void )
> {
> 	cout << "main: creating thread\n";
> 	boost::thread thread(thread_test);
>
> 	cout << "main: sleeping for 2 seconds\n";
> 	sleep(2);
>
> 	cout << "main: trying to lock mutex\n";
> 	boost::try_mutex::scoped_try_lock lock(mutex,true);

This will force a lock (which means we'll block until the thread releases
the lock).

> 	while ( !lock.try_lock() )

Since the above insured the mutex is already locked, this would be a
recursive lock which should result in a thread_lock_error exception being
thrown.  Is this not what's happening for you?

> 		cout << "main: retrying to lock mutex\n";
>
> 	cout << "main: joining thread\n";
> 	thread.join();
>
> 	cout << "main: thread joined\n";
> 	return 0;
> }

William E. Kempf