Re: [Boost-users] [multi_index] thread safety

15 May 2006

      Thanks.. Let me try that out. Also, I will put check if mutex acquire
method returns success or not during
addition only than and than I will go ahead and add procedure in pool.

Thanks
Priyank

________________________________

From: boost-users-bounces@lists.boost.org
[mailto:boost-users-bounces@lists.boost.org] On Behalf Of Kobi
Cohen-Arazi
Sent: Friday, May 12, 2006 11:33 PM
To: boost-users@lists.boost.org
Subject: Re: [Boost-users] [multi_index] thread safety

Hi,

comments below

On 5/12/06, Patel Priyank-PPATEL1  wrote: 

	Hi Joaquin,

	I have to use actually two or more threads on procedure pool. I
start seeing same 
	Problem when I have three/four threads working on same procedure
pool. I tried to introduce mutex (ACE_Guard) but still having problems
in execution in one/two minute of execution.
	Seems I am guarding every method that is used by container.
Anything wrong with the 
	Following code?

	int Procedure_Pool::add_by_id(Procedure * _procedure)
	{
	        LD_TRACE("Procedure_Pool::add_by_id");
	        ACE_ASSERT(_procedure != 0);
	        ACE_DEBUG((LM_DEBUG, "ADDING %d\n", _procedure->id())); 

	        if (find_by_id(_procedure->id()) == 0) {
	                ACE_Guard guard(mutex_);
	                {
	                        // procedure not found
	                        procedure_by_id_.insert(_procedure); 
	                }
	                // debug info
	                ACE_DEBUG((LM_DEBUG, "Added procedure : %d \n",
_procedure->id()));
	                // return success
	                return 0;
	        } else {
	                // error
	                ACE_ERROR((LD_ERROR "%N:%l Error in adding
procedure : %d \n", _procedure->id()));
	                // return failure
	                return -1; 
	        }

	}

	int Procedure_Pool::remove_by_id(Procedure * _procedure)
	{
	        LD_TRACE("Procedure_Pool::remove_by_id");
	        ACE_ASSERT(_procedure != 0);
	        ACE_DEBUG((LM_DEBUG, "REMOVING: %d \n",
_procedure->id())); 
	        if (find_by_id(_procedure->id()) != 0) {
	                ACE_Guard guard(mutex_);
	                {
	                        // procedure found

procedure_by_id_.erase(_procedure->id()); 
	                }
	                ACE_DEBUG((LM_DEBUG, "Removed procedure : %d
\n", _procedure->id()));
	                return 0;
	        } else {
	                ACE_ERROR((LD_ERROR "%N:%l Error in removing
procedure : %d \n", _procedure->id())); 
	                return -1;
	        }

	}

	Procedure * Procedure_Pool::find_by_id(int _id)
	{
	        LD_TRACE("Procedure_Pool::find_by_id");
	        ACE_Guard guard(mutex_); 
	        {
	                Procedure_By_Id::iterator it =
procedure_by_id_.find(_id);
	                if (it != procedure_by_id_.end()) {
	                        ACE_DEBUG((LM_DEBUG, "%N:%l Found
procedure for id: %d \n", _id)); 
	                        return *it;
	                }
	        }
	        ACE_DEBUG((LM_DEBUG, "%N:%l Not able to found procedure
for id: %d \n", _id));
	        // return null
	        return 0;
	}

Yes. There is a small theoretical problem with your code. A possible
race condition. you tried to find_by_id, using mutex, than release that
mutex and reacquire it for erase. That's a possible race condition. The
"find" until the "erase" must be atomic. At least IMHO. 

Kobi.