Ubuntu Manpage: MPI_Iprobe - Nonblocking test for a message.

NAME

       MPI_Iprobe - Nonblocking test for a message.

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Iprobe(int source, int tag, MPI_Comm comm, int *flag,
            MPI_Status *status)

Fortran Syntax

       INCLUDE 'mpif.h'
       MPI_IPROBE(SOURCE, TAG, COMM, FLAG, STATUS, IERROR)
            LOGICAL   FLAG
            INTEGER   SOURCE, TAG, COMM, STATUS(MPI_STATUS_SIZE), IERROR

C++ Syntax

       #include <mpi.h>
       bool Comm::Iprobe(int source, int tag, Status& status) const

       bool Comm::Iprobe(int source, int tag) const

INPUT PARAMETERS

       source    Source rank or MPI_ANY_SOURCE (integer).

       tag       Tag value or MPI_ANY_TAG (integer).

       comm      Communicator (handle).

OUTPUT PARAMETERS

       flag      Message-waiting flag (logical).

       status    Status object (status).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

The MPI_Probe and MPI_Iprobe operations allow checking of incoming messages without actual
receipt of them. The user can then decide how to receive them, based on the information
returned by the probe (basically, the information returned by status). In particular, the
user may allocate memory for the receive buffer, according to the length of the probed
message.

MPI_Iprobe(source, tag, comm, flag, status) returns flag = true if there is a message that
can be received and that matches the pattern specified by the arguments source, tag, and
comm. The call matches the same message that would have been received by a call to
MPI_Recv(..., source, tag, comm, status) executed at the same point in the program, and
returns in status the same value that would have been returned by MPI_Recv(). Otherwise,
the call returns flag = false, and leaves status undefined.

If MPI_Iprobe returns flag = true, then the content of the status object can be
subsequently accessed as described in Section 3.2.5 of the MPI-1 Standard, "Return
Status," to find the source, tag, and length of the probed message.

A subsequent receive executed with the same context, and the source and tag returned in
status by MPI_Iprobe will receive the message that was matched by the probe if no other
intervening receive occurs after the probe. If the receiving process is multithreaded, it
is the user's responsibility to ensure that the last condition holds.

The source argument of MPI_Probe can be MPI_ANY_SOURCE, and the tag argument can be
MPI_ANY_TAG, so that one can probe for messages from an arbitrary source and/or with an
arbitrary tag. However, a specific communication context must be provided with the comm
argument.

If your application does not need to examine the status field, you can save resources by
using the predefined constant MPI_STATUS_IGNORE as a special value for the status
argument.

It is not necessary to receive a message immediately after it has been probed for, and the
same message may be probed for several times before it is received.

NOTE

       Users  of  libmpi-mt  should  remember that two threads may do an MPI_Iprobe that actually
       returns true for the same message for both threads.

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and
       Fortran  routines in the last argument. C++ functions do not return errors. If the default
       error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then  on  error  the  C++  exception
       mechanism will be used to throw an MPI:Exception object.

       Before  the  error value is returned, the current MPI error handler is called. By default,
       this error handler aborts the MPI job, except for I/O function errors. The  error  handler
       may    be   changed   with   MPI_Comm_set_errhandler;   the   predefined   error   handler
       MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not
       guarantee that an MPI program can continue past an error.