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

From: Kobi Cohen-Arazi (kobi.cohenarazi_at_[hidden])
Date: 2006-05-13 00:32:59

Hi,

comments below

On 5/12/06, Patel Priyank-PPATEL1 <priyankpatel_at_[hidden]> 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<ACE_Mutex> 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<ACE_Mutex> 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<ACE_Mutex> 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.