Re: [Boost-users] mpi non-blocking communication

Subject: Re: [Boost-users] mpi non-blocking communication
From: Kraus Philipp (philipp.kraus_at_[hidden])
Date: 2010-12-02 13:20:05

Am 02.12.2010 um 18:00 schrieb Riccardo Murri:

> Hi Philipp,
>
> On Thu, Dec 2, 2010 at 4:12 PM, Philipp Kraus
> <philipp.kraus_at_[hidden]> wrote:
>> There is only one problem at the time:  The CPU 0 does not catch  
>> every
>> message.
>> The main method:
>>
>> MPI::Init_thread( argc, argv, MPI_THREAD_SERIALIZED );
>> mpi::communicator loMPICom;
>> tl::logger::getInstance()->startListener(loMPICom);
>> tl::logger::getInstance()->write(loMPICom, tl::logger::warn, "test  
>> all");
>> tl::logger::getInstance()->shutdownListener(loMPICom);
>> MPI::Finalize();
>>
>>
>> So every process shoudl create a message and the CPU 0 should catch  
>> them
>> all. The write method sends the data with isend (non-blocking).
>> The CPU 0 runs a thread in background with
>>
>> while (m_listenerrunnging) {
>>        while (boost::optional<mpi::status> l_status =
>> p_mpi.iprobe(mpi::any_source, LOGGER_MPI_TAG)) {
>>                        std::string l_str;
>>                p_mpi.recv(  l_status->source(), l_status->tag(),  
>> l_str );
>>        }
>>        boost::this_thread::yield();
>> }
>>
>
> This code for the background thread will only probe for new messages
> until m_listenerrunnging is true; as soon as it turns to false (in
> logger::getInstance()->shutdownListener?), it will stop and receive no
> more messages.
>
> You probably want to make it run until all messages have arrived.  How
> you do this depends on your application: if you know how many messages
> will be coming, just count them; if you don't, make ranks !=1 send an
> "end of transmission" message when they are done and only shutdown the
> listener when all "end of transmission" messages have been received.
> There might be other methods that are more suited to your application.

Okay, that answers my question: It is also my problem to solving the  
transmission. The MPI interface has no implementated code.

>> If I run the program some times, I receive at one run 1 message,
>> sometimes 4 or 5, but it's not deterministic.
>
> MPI guarantees reliable delivery of messages but not within a specific
> timeframe. IOW, messages will be received *if you wait long enough*.
> If you shut down the receiver end too early, messages will be lost.

I think that is the main problem, so I must send a EO? for close all  
transmission.

Thanks

PHil