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

Subject: Re: [Boost-users] mpi non-blocking communication
From: Riccardo Murri (riccardo.murri_at_[hidden])
Date: 2010-11-28 07:42:04

On Sun, Nov 28, 2010 at 1:25 PM, Philipp Kraus
<philipp.kraus_at_[hidden]> wrote:
> I understand the recv in this way, that it waits until a message is send. I
> think if I have no messages, the receive blocks the loop, do it?
> I would like to create the code in that way:
>
> while (...) {
> while mpi-message-is-there
> Â  Â do something
> }
>

Indeed, `recv` is a blocking call.  To receive a message only if one
is available, you need to probe for it first, and then receive.
Something along these lines::

  while(...) {
    while(boost::optional<mpi::status> status =
                               p_comm.iprobe(mpi::any_source, TAG)) {
      // a message is available, receive it
      mpi::recv(status->source(), status->tag(), l_str);
      // process `l_str`
    };
    // ...
  };

Caveat: use `status->source()` and `status->tag()` in the recv call to
ensure you recv the message that you probed for (this may still fail
if you're running iprobe/recv loops in several threads concurrently
within the same MPI process).

Best regards,
Riccardo