[Boost-users] call_once

Subject: [Boost-users] call_once
From: seweryn_at_[hidden]
Date: 2010-06-20 10:27:18

Dears,
I had observed dead lock in call_once (posix code). How to understand
what causes this dead lock?Windows code works well - my usage of
call_once runs normally on windows, but ported to Linuxhangs.
Below I had marked where the code is waiting (endless) - see line
with '// ***'.
I understand that condition "flag.epoch==uninitialized_flag" is not
fullfilled, but"flag.epoch==being_initialized" is passed. So it seems
that:Â pthread_cond_waitis waiting, but I have no clue for what it is
waiting. Especially that I haveno real access to
"detail::once_epoch_cv" - seems to be private member of thenamespace.
Also I observed that there is single hit to that function. The
whileloop is done once - program is entering while and stops on the
first pthread_cond_wait.
template
   void call_once(once_flag
                   try
                   {
                     
 pthread::pthread_mutex_scoped_unlock relocker(
                       f();
                   }
                   catch(...)
                   {
                       flag.epoch=uninitialized_flag;
                     
 BOOST_VERIFY(!pthread_cond_broadcast(
                       throw;
                   }
                   flag.epoch=--detail::once_global_epoch;
                   BOOST_VERIFY(!pthread_cond_broadcast(
               }
               else
               {
                   while(flag.epoch==being_initialized)
                   {
                     
 BOOST_VERIFY(!pthread_cond_wait(&detail::once_epoch_cv, // *** first
hit here causes dead lock
                   }
               }

Best regards,Seweryn Habdank-Wojewodzki.