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.TH "MPI_TEST" "3" "May 30, 2025" "" "Open MPI"
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\fI\%MPI_Test\fP — Tests for the completion of a specific send or receive.
.SH SYNTAX
.SS C Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
#include <mpi.h>

int MPI_Test(MPI_Request *request, int *flag, MPI_Status *status)
.ft P
.fi
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.SS Fortran Syntax
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.INDENT 3.5
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.nf
.ft C
USE MPI
! or the older form: INCLUDE \(aqmpif.h\(aq
MPI_TEST(REQUEST, FLAG, STATUS, IERROR)
     LOGICAL FLAG
     INTEGER REQUEST, STATUS(MPI_STATUS_SIZE), IERROR
.ft P
.fi
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.SS Fortran 2008 Syntax
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.INDENT 3.5
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.nf
.ft C
USE mpi_f08
MPI_Test(request, flag, status, ierror)
     TYPE(MPI_Request), INTENT(INOUT) :: request
     LOGICAL, INTENT(OUT) :: flag
     TYPE(MPI_Status) :: status
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
.ft P
.fi
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.SH INPUT PARAMETER
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.IP \(bu 2
\fBrequest\fP: Communication request (handle).
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.SH OUTPUT PARAMETERS
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.IP \(bu 2
\fBflag\fP: True if operation completed (logical).
.IP \(bu 2
\fBstatus\fP: Status object (status).
.IP \(bu 2
\fBierror\fP: Fortran only: Error status (integer).
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.SH DESCRIPTION
.sp
A call to \fI\%MPI_Test\fP 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 \fBMPI_REQUEST_NULL\fP\&. The call returns flag =
false, otherwise. In this case, the value of the status object is
undefined. \fI\%MPI_Test\fP is a local operation.
.sp
The return status object for a receive operation carries information
that can be accessed as described in the “Return Status” subsection of
the “Point\-to\-Point Communication” chapter in the \fI\%MPI Standard\fP\&. The status object for a send
operation carries information that can be accessed by a call to
\fI\%MPI_Test_cancelled\fP (see the “Probe and Cancel” section of the
\fI\%MPI Standard\fP).
.sp
If your application does not need to examine the \fIstatus\fP field, you can
save resources by using the predefined constant \fBMPI_STATUS_IGNORE\fP as a
special value for the \fIstatus\fP argument.
.sp
One is allowed to call \fI\%MPI_Test\fP 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 \fI\%MPI_Wait\fP and \fI\%MPI_Test\fP can be used to complete both sends
and receives.
.SH NOTES
.sp
The use of the nonblocking \fI\%MPI_Test\fP 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
\fI\%MPI_Test\fP\&.
.SH ERRORS
.sp
Almost all MPI routines return an error value; C routines as the return result
of the function and Fortran routines in the last argument.
.sp
Before the error value is returned, the current MPI error handler associated
with the communication object (e.g., communicator, window, file) is called.
If no communication object is associated with the MPI call, then the call is
considered attached to MPI_COMM_SELF and will call the associated MPI error
handler. When MPI_COMM_SELF is not initialized (i.e., before
\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
Model exclusively) the error raises the initial error handler. The initial
error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error
handler is called for all other MPI functions.
.sp
Open MPI includes three predefined error handlers that can be used:
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.IP \(bu 2
\fBMPI_ERRORS_ARE_FATAL\fP
Causes the program to abort all connected MPI processes.
.IP \(bu 2
\fBMPI_ERRORS_ABORT\fP
An error handler that can be invoked on a communicator,
window, file, or session. When called on a communicator, it
acts as if \fI\%MPI_Abort\fP was called on that communicator. If
called on a window or file, acts as if \fI\%MPI_Abort\fP was called
on a communicator containing the group of processes in the
corresponding window or file. If called on a session,
aborts only the local process.
.IP \(bu 2
\fBMPI_ERRORS_RETURN\fP
Returns an error code to the application.
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.sp
MPI applications can also implement their own error handlers by calling:
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.IP \(bu 2
\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
.IP \(bu 2
\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
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.sp
Note that MPI does not guarantee that an MPI program can continue past
an error.
.sp
See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
.sp
See the Error Handling section of the MPI\-3.1 standard for
more information.
.sp
Note that per the “Return Status” section in the “Point\-to\-Point
Communication” chapter in the \fI\%MPI Standard\fP, MPI errors on requests passed to
\fI\%MPI_Test\fP do not set the \fBstatus.MPI_ERROR\fP field in the
returned \fIstatus\fP\&.  The error code is always passed to the back\-end
error handler and may be passed back to the caller through the return
value of \fI\%MPI_Test\fP if the back\-end error handler returns it.
The pre\-defined MPI error handler \fBMPI_ERRORS_RETURN\fP exhibits this
behavior, for example.
.sp
\fBSEE ALSO:\fP
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.INDENT 3.5
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.IP \(bu 2
\fI\%MPI_Comm_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_File_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_Testall\fP
.IP \(bu 2
\fI\%MPI_Testany\fP
.IP \(bu 2
\fI\%MPI_Testsome\fP
.IP \(bu 2
\fI\%MPI_Wait\fP
.IP \(bu 2
\fI\%MPI_Waitall\fP
.IP \(bu 2
\fI\%MPI_Waitany\fP
.IP \(bu 2
\fI\%MPI_Waitsome\fP
.IP \(bu 2
\fI\%MPI_Win_set_errhandler\fP
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.SH COPYRIGHT
2003-2025, The Open MPI Community
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