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MPI_Iprobe - Nonblocking test for a message.
#include <mpi.h>
int MPI_Iprobe(int source, int tag, MPI_Comm comm, int *flag,
MPI_Status *status)
INCLUDE ’mpif.h’
MPI_IPROBE(SOURCE, TAG, COMM, FLAG, STATUS, IERROR)
LOGICAL FLAG
INTEGER SOURCE, TAG, COMM, STATUS(MPI_STATUS_SIZE), IERROR
#include <mpi.h>
bool Comm::Iprobe(int source, int tag, Status& status) const
bool Comm::Iprobe(int source, int tag) const
- source
- Source rank or MPI_ANY_SOURCE (integer).
- tag
- Tag
value or MPI_ANY_TAG (integer).
- comm
- Communicator (handle).
- flag
- Message-waiting flag (logical).
- status
- Status object (status).
- IERROR
- Fortran
only: Error status (integer).
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.
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.
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.
MPI_Probe
MPI_Cancel
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