Re: [boost] recursive_mutex problem on joining

From: Anthony Williams (anthony_w.geo_at_[hidden])
Date: 2007-03-27 05:30:45

"Steve Weber" <steve.weber.junk_at_[hidden]> writes:

> Im kinda noob only 2 years of c++
>
> When joining two threads using a recursive_mutex.  The recursive_mutex is
> not shared resulting in dead lock.
> Is this a "bug" or am i missing something.

You are missing something: you are trying to join whilst holding the mutex
that the thread you are waiting for is trying to acquire.

Also, a plain mutex will work fine here.

> also what would be a good solution to this?

Unlock the mutex before you try and join. As a rule of thumb, you shouldn't do
blocking operations (e.g. join) whilst you have a mutex locked.

> Example code of my problem.
> ----------------------------------------------------------------------
>
> class Test{
> public:
>     boost::recursive_mutex m_mutex;
>     boost::thread* m_thread;
>     bool m_endThread;
>     // start thread
>     Test() : m_endThread( false ) {
>         m_thread = new boost::thread( boost::bind( &Test::threaded, this )
> );
>     }
>     // cleanup
>     virtual ~Test() {
>         boost::recursive_mutex::scoped_lock l( m_mutex );
>         m_endThread = true;
>         m_thread->join(); //< DEAD LOCK

>         delete m_thread;
>     }
>     // the thread that will block
>     void threaded() {
>         for (;;){
>             boost::recursive_mutex::scoped_lock l( m_mutex ); //< DEAD LOCK
>             if ( m_endThread ) return;
>         }
>     }
> };
>
> int main() {
>     Test t;
> }
>
> ----------------------------------------------------------------------
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>

Anthony
-- 
Anthony Williams
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