Re: [Boost-users] [EXTERNAL] bjam hangs on select (in develop branch)

Subject: Re: [Boost-users] [EXTERNAL] bjam hangs on select (in develop branch)
From: Belcourt, Kenneth (kbelco_at_[hidden])
Date: 2014-10-24 18:52:49

On Oct 24, 2014, at 4:43 PM, Belcourt, Kenneth <kbelco_at_[hidden]> wrote:

> On Oct 24, 2014, at 4:33 PM, Belcourt, Kenneth <kbelco_at_[hidden]> wrote:
> 
>> On Oct 24, 2014, at 7:56 AM, Alain Miniussi <alain.miniussi_at_oca.eu> wrote:
>> 
>>> On 24/10/2014 15:33, Alain Miniussi wrote:
>>>> I did a gnu/openmpi 1.8.2 build on ubuntu which exhibit the same problem.
>>> It did not, just forgot to edit a field in project-config.jam. Only the intel mpiexec/run hangs.
>>>> 
>>>> Can the fact that the setgpid system calls fails be an issue ?
>> 
>> Perhaps.  We make the forked child process it’s own process group leader so that if it’s an MPI job and it dies, all the MPI ranks are cleaned up as well.  We’ve been using this syntax for a number of years on multiple platforms without issues so I’m a little surprised it fails on Ubuntu with OpenMPI 1.8.2  That said, it’s possible that there’s a race condition that you’re able to tickle.
>> 
>> For example, we fork the child process and right before we exec the child process, we set the child process group.  We also set the child process group in the parent process as well.  Perhaps we should on do this once, not twice (i.e. only in the child or only in the parent, not both).  Or perhaps there’s a race if both the child and parent call to setpgid runs concurrently.
> 
> Just pushed this commit, 7bcbc5ac31ab1, to develop which adds checks to the setpgid calls and, if they fail, indicates whether it was the parent or child process who called.  Can you give this a try and let me know which call is failing?

Well I be danged.  I was just testing thie change on my Mac and found this in the output:

        setpgid (parent): Permission denied

So it seems we’ve been ignoring this problem for some time and didn’t know it.  That would be my bad.  Let me work on a fix (will probably remove the duplicate call in the parent process).

— Noel