On Tuesday, March 11, 2008 5:05 AM Yasmina Berber wrote:

Sent: To: boost-users@lists.boost.org Subject: [Boost-users] [Mutex] behaviour??

Hi, everybody I have a problem to understand mutex behaviour in a server client program . basically there are two threads that execute different code in two different classes but manipulate the same resource: fisrt Class is Subscriber with these members :

public: ACE_Unbounded_Set m_set; typedef boost::recursive_mutex Mutex; typedef boost::recursive_mutex::scoped_lock Lock; Mutex mutex_set;

and methods: Subscribe (client_reference) : inserts (add) a reference client to the set { ... Lock theScope( mutex_set); m_set.insert (client_reference) ... } Unsubscribe(client_reference) : removes a reference client from the set { ... Lock theScope( mutex_set); m_set.remove (client_reference) }

...

mutex_set) for (Subscriber::Set_Iterator iter (subscriberPtr->m_set); iter.next (...) != 0 ; iter.advance ()) { specific opeartion on each client reference } } What happens is that a client can be removed (call to Unsubscribe()) by

the second class is Manager that has a shared pointer to Subscriber (SubscriberPtr) and does a specific opeartion on each client_reference inside a for loop in the method Manage() { boost::recursive_mutex::scoped_lock scoped_lock(subscriberPtr- the first thread during the second one is executing manage() : the set is not well protected and this causes of course seg fault.

I probably do something wrong, If you need more details please let me know. Regards.

If your code is exactly as you have it here I see nothing wrong with it. You are locking the mutex inside Manage so it is not possible for another thread to enter Unsubscribe. Could it be that some action inside Manage is the one calling Unsubscribe (i.e. from the same thread)? Could it be that you are copying your instance of Subscriber somewhere so the instance of Subscriber inside Manage (subscriberPtr) is not the same as the instance of subscriber on which Unsubscribe gets called? If you put together a small sample program showing your problem I'll be happy to take a look. -delfin