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Subject: Re: [OMPI users] Multi-threading with OpenMPI ?
From: Ashika Umanga Umagiliya (aumanga_at_[hidden])
Date: 2009-09-17 23:52:17


Thanks Ralph,

I have not much experience in this area.shall i use
pthread_mutex_lock(*),*pthread_mutex_unlock() ..etc or following which i
saw in OpenMPI source :

static opal_mutex_t ompi_lock;

OPAL_THREAD_LOCK(&ompi_lock);
   //
OPAL_THREAD_UNLOCK(&ompi_lock);

Thanks in advance,
umanga

Ralph Castain wrote:
> 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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