[Ace-users] [ace-users] ACE_Process_Manager problem

[Douglas C. Schmidt]

Hi Oliver,

   Thanks for using the PRF!

>     ACE VERSION: 5.6.1
> 
>     HOST MACHINE and OPERATING SYSTEM:
> Linux, Fedora Core 5
> 
>     TARGET MACHINE and OPERATING SYSTEM, if different from HOST:
>     COMPILER NAME AND VERSION (AND PATCHLEVEL):
> 
>     THE $ACE_ROOT/ace/config.h FILE 
> config_linux.h
> 
>     THE $ACE_ROOT/include/makeinclude/platform_macros.GNU FILE
> platform_linux.GNU
> 
>     SYNOPSIS:
> Problem spawning process with ACE_Process_Manager while waiting for end
> of another process
> 
>     DESCRIPTION:
> I spawn several processes using ACE_Process_Manager. The problem is,
> while I wait() for a process, further spawn()'s won't return.
> 
>     REPEAT BY:
> I tracked this down to the following ACE code:
> in Process_Manager.cpp, spawn(), we have (line 446...):
>   pid_t const pid = process->spawn (options);
> 
>   // Only include the pid in the parent's table.
>   if (pid == ACE_INVALID_PID || pid == 0)
>     return pid;
> 
>   ACE_MT (ACE_GUARD_RETURN (ACE_Recursive_Thread_Mutex,
>                             ace_mon, this->lock_, -1));
> 
>   if (this->append_proc (process, event_handler) == -1)
>     // bad news: spawned, but not registered in table.
>     return ACE_INVALID_PID;
> ------------------------------------------------------------------------
> ------------
> in Process_Manager.cpp, wait(), we have (line 789...):
>   ACE_MT (ACE_GUARD_RETURN (ACE_Recursive_Thread_Mutex, ace_mon,
> this->lock_, -1));
> 
>   if (pid != 0)
>     {
>       idx = this->find_proc (pid);
>       if (idx == -1)
>         return ACE_INVALID_PID;
>       else
>         proc = process_table_[idx].process_;
>     }
> 
>   if (proc != 0)
>     pid = proc->wait (timeout, status);
> ------------------------------------------------------------------------
> -------------
> 
> This means, spawn() tries to acquire this->lock_, which is already hold
> by wait().
> Is this the way, ACE_Process_Manager should work?
> Isn't it possible to release the lock_ after the access to the
> process_table (find_proc()), and acquire it again after the wait()?

That's certainly worth a try.  Could you please

. Make those changes and send us patches?

. Update the ACE_ROOT/tests/Process_Manager_Test.cpp file to test for
  the usecase that's failing for you so we'll have a regression test for
  this in the future?

thanks,

        Doug

> 
>     SAMPLE FIX/WORKAROUND:
> My workaround is to wait with this code, not very nice ;-)
>     while ((iResult=ACE_Process_Manager::instance ()->wait (iProcessId,
> TIME_100ms, &t_Status)==0))
>     {
>         ACE_Thread::yield ();
>     }
> 
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