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Subject: Re: [OMPI users] Multi-threading with OpenMPI ?
From: Ashika Umanga Umagiliya (aumanga_at_[hidden])
Date: 2009-09-17 21:44:11

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
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
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,

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.