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
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_IPROBE(SOURCE, TAG, COMM, FLAG, STATUS, IERROR)
LOGICAL FLAG
INTEGER SOURCE, TAG, COMM, STATUS(MPI_STATUS_SIZE), IERROR
Fortran 2008 Syntax
USE mpi_f08
MPI_Iprobe(source, tag, comm, flag, status, ierror)
INTEGER, INTENT(IN) :: source, tag
TYPE(MPI_Comm), INTENT(IN) :: comm
LOGICAL, INTENT(OUT) :: flag
TYPE(MPI_Status) :: status
INTEGER, OPTIONAL, INTENT(OUT) :: 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 mes-
sages without actual receipt of them. The user can then decide how to
receive them, based on the information returned by the probe (basi-
cally, 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 ob-
ject 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 re-
sponsibility to ensure that the last condition holds.
The source argument of MPI_Probe can be MPI_ANY_SOURCE, and the tag ar-
gument 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 com-
munication 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++ func-
tions 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
4.1.2 Nov 24, 2021 MPI_Iprobe(3)
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