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

13 May 2006

      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.

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

Kobi Cohen-Arazi