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Subject: Re: [OMPI users] Multi-threading with OpenMPI ?
From: Ralph Castain (rhc_at_[hidden])
Date: 2009-09-17 23:36:48

Only thing I can suggest is to place a thread lock around the call to
comm_spawn so that only one thread at a time can execute that
function. The call to mpi_init_thread is fine - you just need to
explicitly protect the call to comm_spawn.

On Sep 17, 2009, at 7:44 PM, Ashika Umanga Umagiliya wrote:

> HI Jeff, Ralph,
> Yes, I call MPI_COMM_SPAWN in multiple threads simultaneously.
> Because I need to expose my parallel algorithm as a web service, I
> need multiple clients connect and execute my logic as same time(ie
> mutiple threads).
> For each client , a new thread is created (by Web service framework)
> and inside the thread,MPI_Init_Thread() is called if the MPI hasnt
> been initialized.
> The the thread calls MPI_COMM__SPAWN and create new processes.
> So ,if this is the case isn't there any workarounds ?
> Thanks in advance,
> umanga
> Jeff Squyres wrote:
>> On Sep 16, 2009, at 9:53 PM, Ralph Castain wrote:
>>> Only the obvious, and not very helpful one: comm_spawn isn't thread
>>> safe at this time. You'll need to serialize your requests to that
>>> function.
>> This is likely the cause of your issues if you are calling
>> MPI_COMM_SPAWN in multiple threads simultaneously. Can you verify?
>> If not, we'll need to dig a little deeper to figure out what's
>> going on. But Ralph is right -- read up on the THREAD_MULTIPLE
>> constraints (check the OMPI README file) to see if that's what's
>> biting you.
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