.\" -*- nroff -*-
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" Copyright 2007-2008 Cisco Systems, Inc.  All rights reserved.
.\" $COPYRIGHT$
.TH MPI_Test 3 "May 26, 2022" "4.1.4" "Open MPI"
.SH NAME
\fBMPI_Test\fP \- Tests for the completion of a specific send or receive.

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Test(MPI_Request *\fIrequest\fP, int\fI *flag\fP, MPI_Status\fI *status\fP)

.fi
.SH Fortran Syntax
.nf
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_TEST(\fIREQUEST, FLAG, STATUS, IERROR\fP)
	LOGICAL	\fIFLAG\fP
	INTEGER	\fIREQUEST, STATUS(MPI_STATUS_SIZE), IERROR\fP

.fi
.SH Fortran 2008 Syntax
.nf
USE mpi_f08
MPI_Test(\fIrequest\fP, \fIflag\fP, \fIstatus\fP, \fIierror\fP)
	TYPE(MPI_Request), INTENT(INOUT) :: \fIrequest\fP
	LOGICAL, INTENT(OUT) :: \fIflag\fP
	TYPE(MPI_Status) :: \fIstatus\fP
	INTEGER, OPTIONAL, INTENT(OUT) :: \fIierror\fP

.fi
.SH C++ Syntax
.nf
#include <mpi.h>
bool Request::Test(Status& \fIstatus\fP)

bool Request::Test()

.fi
.SH INPUT PARAMETER
.ft R
.TP 1i
request
Communication request (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
flag
True if operation completed (logical).
.TP 1i
status
Status object (status).
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
A call to MPI_Test returns flag = true if the operation identified by request is complete. In such a case, the status object is set to contain information on the completed operation; if the communication object was created by a nonblocking send or receive, then it is deallocated and the request handle is set to MPI_REQUEST_NULL. The call returns flag = false, otherwise. In this case, the value of the status object is undefined. MPI_Test is a local operation.
.sp
The return status object for a receive operation carries information that can be accessed as described in Section 3.2.5 of the MPI-1 Standard, "Return Status." The status object for a send operation carries information that can be accessed by a call to MPI_Test_cancelled (see Section 3.8 of the MPI-1 Standard, "Probe and Cancel").
.sp
If your application does not need to examine the \fIstatus\fP field, you can save resources by using the predefined constant MPI_STATUS_IGNORE as a special value for the \fIstatus\fP argument.
.sp
One is allowed to call MPI_Test with a null or inactive \fIrequest\fP argument. In such a case the operation returns with \fIflag\fP = true and empty \fIstatus\fP.
.sp
The functions MPI_Wait and MPI_Test can be used to complete both sends and
receives.

.SH NOTES
The use of the nonblocking MPI_Test call allows the user to schedule alternative activities within a single thread of execution. An event-driven thread scheduler can be emulated with periodic calls to MPI_Test.

.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. 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.
.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, MPI_File_set_errhandler, or
MPI_Win_set_errhandler (depending on the type of MPI handle that
generated the request); 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.
.sp
Note that per MPI-1 section 3.2.5, MPI exceptions on requests passed
to MPI_TEST do not set the status.MPI_ERROR field in the returned
status.  The error code is passed to the back-end error handler
and may be passed back to the caller through the return value of
MPI_TEST if the back-end error handler returns it.  The
pre-defined MPI error handler MPI_ERRORS_RETURN exhibits this
behavior, for example.

.SH SEE ALSO
.ft R
.sp
MPI_Comm_set_errhandler
.br
MPI_File_set_errhandler
.br
MPI_Testall
.br
MPI_Testany
.br
MPI_Testsome
.br
MPI_Wait
.br
MPI_Waitall
.br
MPI_Waitany
.br
MPI_Waitsome
.br
MPI_Win_set_errhandler
.br