MPIProbe(3OpenMPI) MPIProbe(3OpenMPI)

NAME
       MMPPIIPPrroobbee - Blocking test for a message.


SSYYNNTTAAXX
CC SSyynnttaaxx
       #include 
       int MPIProbe(int source, int tag, MPIComm comm, MPIStatus *status)


FFoorrttrraann SSyynnttaaxx
       INCLUDE 'mpif.h'
       MPIPROBE(SOURCE, TAG, COMM, STATUS, IERROR)
            INTEGER   SOURCE, TAG, COMM, STATUS(MPISTATUSSIZE), IERROR


CC++++ SSyynnttaaxx
       #include 
       void Comm::Probe(int source, int tag, Status& status) const

       void Comm::Probe(int source, int tag) const


IINNPPUUTT PPAARRAAMMEETTEERRSS
       source    Source rank or MPIANYSOURCE (integer).

       tag       Tag value or MPIANYTAG (integer).

       comm      Communicator (handle).


OOUUTTPPUUTT PPAARRAAMMEETTEERRSS
       status    Status object (status).

       IERROR    Fortran only: Error status (integer).


DESCRIPTION
       The MPIProbe and MPIIprobe operations allow checking of incoming mes-
       sages, without actual receipt of them. The user can then decide how  to
       receive  them,  based  on  the information returned by the probe in the
       status variable. For example, the user  may  allocate  memory  for  the
       receive buffer, according to the length of the probed message.

       MPIProbe  behaves  like  MPIIprobe  except that it is a blocking call
       that returns only after a matching message has been found.

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

       The semantics of MPIProbe and MPIIprobe guarantee progress: If a call
       to  MPIProbe has been issued by a process, and a send that matches the
       probe has been initiated by some process, then the  call  to  MPIProbe
       will  return,  unless  the  message  is  received by another concurrent
       receive operation (that is executed by another thread  at  the  probing
       process).  Similarly,  if  a  process  busy waits with MPIIprobe and a
       matching message has been issued, then  the  call  to  MPIIprobe  will
       eventually return flag = true unless the message is received by another
       concurrent receive operation.

       EExxaammppllee 11:: Use blocking probe to wait for an incoming message.

       CALL MPICOMMRANK(comm, rank, ierr)
              IF (rank.EQ.0) THEN
                   CALL MPISEND(i, 1, MPIINTEGER, 2, 0, comm, ierr)
              ELSE IF(rank.EQ.1) THEN
                   CALL MPISEND(x, 1, MPIREAL, 2, 0, comm, ierr)
              ELSE   ! rank.EQ.2
                  DO i=1, 2
                     CALL MPIPROBE(MPIANYSOURCE, 0,
                                     comm, status, ierr)
                     IF (status(MPISOURCE) = 0) THEN
       100                CALL MPIRECV(i, 1, MPIINTEGER, 0, 0, status, ierr)
                     ELSE
       200                CALL MPIRECV(x, 1, MPIREAL, 1, 0, status, ierr)
                     END IF
                  END DO
              END IF

       Each message is received with the right type.

       EExxaammppllee 22:: A program similar to the previous example, but with a  prob-
       lem.

       CALL MPICOMMRANK(comm, rank, ierr)
              IF (rank.EQ.0) THEN
                   CALL MPISEND(i, 1, MPIINTEGER, 2, 0, comm, ierr)
              ELSE IF(rank.EQ.1) THEN
                   CALL MPISEND(x, 1, MPIREAL, 2, 0, comm, ierr)
              ELSE
                  DO i=1, 2
                     CALL MPIPROBE(MPIANYSOURCE, 0,
                                     comm, status, ierr)
                     IF (status(MPISOURCE) = 0) THEN
       100                CALL MPIRECV(i, 1, MPIINTEGER, MPIANYSOURCE,
                                        0, status, ierr)
                     ELSE
       200                CALL MPIRECV(x, 1, MPIREAL, MPIANYSOURCE,
                                        0, status, ierr)
                     END IF
                  END DO
              END IF

       We  slightly  modified  Example  2,  using MPIANYSOURCE as the source
       argument in the two receive calls in statements labeled  100  and  200.
       The  program is now incorrect: The receive operation may receive a mes-
       sage that is distinct from the message probed by the preceding call  to
       MPIProbe.


EERRRROORRSS
       Almost  all MPI routines return an error value; C routines as the value
       of the function and Fortran routines in the last  argument.  C++  func-
       tions  do  not  return  errors.  If the default error handler is set to
       MPI::ERRORSTHROWEXCEPTIONS, 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
       MPICommseterrhandler; the predefined error handler MPIERRORSRETURN
       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.


SEE ALSO
       MPIIprobe
       MPICancel




Open MPI 1.2                    September 2006             MPIProbe(3OpenMPI)