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Subject: Re: [OMPI users] openmpi MPI_Init doesn't work after fork under gdb
From: Ralph Castain (rhc_at_[hidden])
Date: 2013-02-21 19:28:31


Hmmm...how about that? Yeah, it doesn't work with the devel trunk either - I'd missed that point.

No idea why, I'm afraid - never tried it before. Are you sure it "crashes"? I'm still getting a child status of "0", but no message output. My guess is that the I/O is being lost for some reason.

On Feb 21, 2013, at 4:09 PM, Geoffrey Irving <irving_at_[hidden]> wrote:

> Actually, I don't see it printing "We're an MPI program!" under gdb,
> which means it isn't working.
>
> Geoffrey
>
> On Thu, Feb 21, 2013 at 4:07 PM, Ralph Castain <rhc_at_[hidden]> wrote:
>> Hmmm...works with 1.6.4 for me on Mac 10.8.2:
>>
>> Ralphs-iMac:v1.6 rhc$ ./fork-bug
>> We're an MPI program!
>> child status = 0
>> Ralphs-iMac:v1.6 rhc$ gdb ./fork-bug
>> GNU gdb 6.3.50-20050815 (Apple version gdb-1820) (Sat Jun 16 02:40:11 UTC 2012)
>> Copyright 2004 Free Software Foundation, Inc.
>> GDB is free software, covered by the GNU General Public License, and you are
>> welcome to change it and/or distribute copies of it under certain conditions.
>> Type "show copying" to see the conditions.
>> There is absolutely no warranty for GDB. Type "show warranty" for details.
>> This GDB was configured as "x86_64-apple-darwin"...Reading symbols for shared libraries ... done
>>
>> (gdb) r
>> Starting program: /Volumes/RHCHD/rhc/openmpi/v1.6/fork-bug
>> Reading symbols for shared libraries ++............................. done
>> child status = 0
>>
>> Program exited normally.
>> (gdb)
>>
>> Afraid I have no idea why you might be hitting the problem, though...
>>
>>
>> On Feb 21, 2013, at 3:50 PM, Geoffrey Irving <irving_at_[hidden]> wrote:
>>
>>> The singleton fork/exec itself is fine, since normal MPI programs work
>>> under gdb (e.g., fork-bug.c without the fork). gdb is has
>>> follow-fork-mode set to parent, so it's odd that gdb is looking at the
>>> child process's trickery at all.
>>>
>>> I've confirmed that it's still broken under 1.6.4, unfortunately.
>>>
>>> Geoffrey
>>>
>>> On Thu, Feb 21, 2013 at 3:36 PM, Ralph Castain <rhc_at_[hidden]> wrote:
>>>> Singletons fork/exec a daemon to support them - my guess is that gdb may not like it on your machine?
>>>>
>>>> FWIW - it runs fine for me using the developer's trunk. You might try with 1.6.4 in case it's a bug in 1.6.0
>>>>
>>>>
>>>> On Feb 21, 2013, at 3:18 PM, Geoffrey Irving <irving_at_[hidden]> wrote:
>>>>
>>>>> The attached program illustrates the problem. It forks, and the child
>>>>> calls MPI_Init. This works fine unless I'm inside gdb. Inside gdb,
>>>>> MPI_Init silently crashes.
>>>>>
>>>>> I'm using OpenMPI 1.6.0 on Mac 10.8.2. I'm running the program
>>>>> directly, not through mpirun.
>>>>>
>>>>> Any ideas what might be wrong?
>>>>>
>>>>> Thanks,
>>>>> Geoffrey
>>>>>
>>>>> cone:scratch% /usr/local/bin/mpicc -o fork-bug fork-bug.c
>>>>> cone:scratch% ./fork-bug
>>>>> We're an MPI program!
>>>>> child status = 0
>>>>> cone:scratch% gdb ./fork-bug
>>>>> gdb ./fork-bug
>>>>> GNU gdb 6.3.50-20050815 (Apple version gdb-1824) (Thu Nov 15 10:42:43 UTC 2012)
>>>>> Copyright 2004 Free Software Foundation, Inc.
>>>>> GDB is free software, covered by the GNU General Public License, and you are
>>>>> welcome to change it and/or distribute copies of it under certain conditions.
>>>>> Type "show copying" to see the conditions.
>>>>> There is absolutely no warranty for GDB. Type "show warranty" for details.
>>>>> This GDB was configured as "x86_64-apple-darwin"...Reading symbols for
>>>>> shared libraries ... done
>>>>>
>>>>> (gdb) run
>>>>> Reading symbols for shared libraries ++............................. done
>>>>> child status = 5
>>>>>
>>>>> Program exited normally.
>>>>> (gdb) cone:scratch%
>>>>> <fork-bug.c>_______________________________________________
>>>>> users mailing list
>>>>> users_at_[hidden]
>>>>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>>>
>>>>
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