MPI_WAIT, MPI_Wait

Purpose

Waits for a nonblocking operation to complete.

C synopsis

#include <mpi.h>
int MPI_Wait(MPI_Request *request,MPI_Status *status);

C++ synopsis

#include mpi.h
void MPI::Request::Wait();

#include mpi.h
void MPI::Request::Wait(MPI::Status& status);

FORTRAN synopsis

include 'mpif.h' or use mpi
MPI_WAIT(INTEGER REQUEST,INTEGER STATUS(MPI_STATUS_SIZE),INTEGER IERROR)

Description

MPI_WAIT returns after the operation identified by request completes. If
the object associated with request was created by a nonblocking operation,
the object is deallocated and request is set to MPI_REQUEST_NULL. MPI_WAIT
is a non-local operation.

You can call MPI_WAIT with a null or inactive request argument. The
operation returns immediately. The status argument returns tag =
MPI_ANY_TAG, source = MPI_ANY_SOURCE. The status argument is also
internally configured so that calls to MPI_GET_COUNT and MPI_GET_ELEMENTS
return count = 0. This is called an empty status.

Information on the completed operation is found in status. You can query
the status object for a send or receive operation with a call to
MPI_TEST_CANCELLED. For receive operations, you can also retrieve
information from status with MPI_GET_COUNT and MPI_GET_ELEMENTS. If
wildcards were used by the receive for either the source or tag, the actual
source and tag can be retrieved by:

     In C:
          source = status.MPI_SOURCE
          tag = status.MPI_TAG
     In FORTRAN:
          source = status(MPI_SOURCE)
          tag = status(MPI_TAG)

The error field of MPI_Status is never modified. The success or failure is
indicated by the return code only.

Passing MPI_STATUS_IGNORE for the status argument causes PE MPI to skip
filling in the status fields. By passing this value for status, you can
avoid having to allocate a status object in programs that do not need to
examine the status fields.

When one of the MPI wait or test calls returns status for a nonblocking
operation request and the corresponding blocking operation does not provide
a status argument, the status from this wait or test call does not contain
meaningful source, tag, or message size information.

When you use this subroutine in a threads application, make sure that the
wait for a given request is done on only one thread. The wait does not have
to be done on the thread that created the request. See IBM Parallel
Environment for AIX: MPI Programming Guide for more information on
programming with MPI in a threads environment.

Parameters

request
     is the request to wait for (handle) (INOUT)
status
     is the status object (Status) (INOUT). Note that in FORTRAN a single
     status object is an array of integers.
IERROR
     is the FORTRAN return code. It is always the last argument.

Errors

A GRequest free function returned an error

A GRequest query function returned an error

Invalid status ignore value

Invalid form of status ignore

Invalid request handle

Truncation occurred

MPI not initialized

MPI already finalized

Develop mode error if:

Illegal buffer update (ISEND)

Inconsistent datatype (MPE_I collectives)

Inconsistent message length (MPE_I collectives)

Inconsistent op (MPE_I collectives)

Match of blocking and non-blocking collectives (MPE_I collectives)

Related information

     MPI_TEST
     MPI_WAITALL
     MPI_WAITANY
     MPI_WAITSOME