MPI_Iprobe(3)                      Open MPI                      MPI_Iprobe(3)



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.


SEE ALSO
       MPI_Probe
       MPI_Cancel




1.4.1                            Jan 14, 2010                    MPI_Iprobe(3)
