.\" -*- nroff -*-
.\" Copyright 2012 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" Copyright (c) 2020      Google, LLC. All rights reserved.
.\" $COPYRIGHT$
.TH MPI_Imrecv 3 "#OMPI_DATE#" "#PACKAGE_VERSION#" "#PACKAGE_NAME#"
.SH NAME
\fBMPI_Imrecv\fP \- Non-blocking receive for a matched message

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Imrecv(void \fI*buf\fP, int\fI count\fP, MPI_Datatype\fI type\fP,
	MPI_Message\fI *message\fP, MPI_Request\fI *request\fP)

.fi
.SH Fortran Syntax
.nf
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_IMRECV(\fIBUF, COUNT, DATATYPE, MESSAGE, REQUEST, IERROR\fP)
	<type>	\fIBUF(*)\fP
	INTEGER	\fICOUNT, DATATYPE, MESSAGE, REQUEST, IERROR\fP

.fi
.SH Fortran 2008 Syntax
.nf
USE mpi_f08
MPI_Imrecv(\fIbuf\fP, \fIcount\fP, \fIdatatype\fP, \fImessage\fP, \fIrequest\fP, \fIierror\fP)
	TYPE(*), DIMENSION(..), ASYNCHRONOUS :: \fIbuf\fP
	INTEGER, INTENT(IN) :: \fIcount\fP
	TYPE(MPI_Datatype), INTENT(IN) :: \fIdatatype\fP
	TYPE(MPI_Message), INTENT(INOUT) :: \fImessage\fP
	TYPE(MPI_Request), INTENT(OUT) :: \fIrequest\fP
	INTEGER, OPTIONAL, INTENT(OUT) :: \fIierror\fP

.fi
.SH INPUT PARAMETERS
.ft R
.TP 1i
count
Number of elements to receive (nonnegative integer).
.TP 1i
datatype
Datatype of each send buffer element (handle).
.TP 1i
message
Message (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
buf
Initial address of receive buffer (choice).
.TP 1i
request
Request (handle).
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
The functions MPI_Mrecv and MPI_Imrecv receive messages that have been
previously matched by a matching probe.
.sp
The \fIrequest\fP returned from MPI_Imrecv can be used with any of the
MPI_Test and MPI_Wait variants, like any non-blocking receive request.
.sp
If MPI_Imrecv is called with MPI_MESSAGE_NULL as the message argument,
a call to one of the MPI_Test or MPI_Wait variants will return
immediately with the \fIstatus\fP object set to \fIsource\fP =
MPI_PROC_NULL, \fItag\fP = MPI_ANY_TAG, and \fIcount\fP = 0, as if a
receive from MPI_PROC_NULL was issued.
.sp
If reception of a matched message is started with MPI_Imrecv, then it
is possible to cancel the returned request with MPI_Cancel. If
MPI_Cancel succeeds, the matched message must be found by a subsequent
message probe (MPI_Probe, MPI_Iprobe, MPI_Mprobe, or MPI_Improbe),
received by a subsequent receive operation or canceled by the
sender.
.sp
Note, however, that is it possible for the cancellation of operations
initiated with MPI_Imrecv to fail.  An example of a failing case is
when canceling the matched message receive would violate MPI message
ordering rules (e.g., if another message matching the same message
signature has matched -- and possible received -- before this
MPI_Imrecv is canceled).

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value
of the function and Fortran routines in the last argument.
.sp
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.

.SH SEE ALSO
.ft R
.nf
MPI_Mprobe
MPI_Improbe
MPI_Probe
MPI_Iprobe
MPI_Imrecv
MPI_Cancel