Re: [Boost-users] [Mutex] behaviour??

From: Sakharuk, Vlad \(GMI Development\) (Vlad_Sakharuk_at_[hidden])
Date: 2008-03-25 13:23:07

I think u are crashing not because of mutex.
The problem is here:
iter.next (...) != 0 ;

should be iter.next != ... end()

-----Original Message-----
From: boost-users-bounces_at_[hidden]
[mailto:boost-users-bounces_at_[hidden]] On Behalf Of Yasmina Berber
Sent: Tuesday, March 11, 2008 8:05 AM
To: boost-users_at_[hidden]
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<client_reference> 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) }

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->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 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.

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