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.TH "MPIX_COMM_GET_FAILED" "3" "May 30, 2025" "" "Open MPI"
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.sp
\fI\%MPIX_Comm_get_failed\fP \- Obtain a group that lists failed processes
in a communicator.
.sp
This is part of the User Level Fault Mitigation \fI\%ULFM extension\fP\&.
.SH SYNTAX
.SS C Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
#include <mpi.h>
#include <mpi\-ext.h>

int MPIX_Comm_get_failed(MPI_Comm comm, MPI_Group *failedgrp)
.ft P
.fi
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.SS Fortran Syntax
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.INDENT 3.5
.sp
.nf
.ft C
USE MPI
USE MPI_EXT
! or the older form: INCLUDE \(aqmpif.h\(aq

MPIX_COMM_GET_FAILED(COMM, FAILEDGRP, IERROR)
     INTEGER COMM, FAILEDGRP, 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
USE mpi_ext_f08

MPIX_Comm_get_failed(comm, failedgrp, ierror)
     TYPE(MPI_Comm), INTENT(IN) :: comm
     TYPE(MPI_Group), INTENT(OUT) :: failedgrp
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
.ft P
.fi
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.SH INPUT PARAMETERS
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.IP \(bu 2
\fBcomm\fP: Communicator (handle).
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.SH OUTPUT PARAMETERS
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.IP \(bu 2
\fBfailedgrp\fP: Group (handle).
.IP \(bu 2
\fBierror\fP: Fortran only: Error status (integer).
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.SH DESCRIPTION
.sp
This local operation returns the group \fIfailedgrp\fP of processes from the
communicator \fIcomm\fP that are locally known to have failed.
The \fIfailedgrp\fP can be empty, that is, equal to MPI_GROUP_EMPTY.
.sp
For any two groups obtained from calls to that routine at the same MPI
process, with the same \fIcomm\fP, the intersection of the largest group with
the smallest group is MPI_IDENT to the smallest group, that is, the same
processes have the same ranks in the two groups, up to the size of the
smallest group.
.SH PROCESS FAILURES
.sp
MPI makes no assumption about asynchronous progress of the failure detection.
A valid MPI implementation may choose to update the group of locally known
failed MPI processes only when it enters a function that must raise a fault
tolerance error.
.sp
It is possible that only the calling MPI process has detected the reported
failure. If global knowledge is necessary, MPI processes detecting failures
should call \fI\%MPIX_Comm_revoke\fP to enforce an error at other ranks.
.SH WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR
.sp
When the communicator is an inter\-communicator, the value of \fIfailedgrp\fP
contains the members known to have failed in both the local and the remote
groups of \fIcomm\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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\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
\fBSEE ALSO:\fP
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.IP \(bu 2
\fI\%MPIX_Comm_revoke\fP
.IP \(bu 2
\fI\%MPIX_Comm_ack_failed\fP
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.SH COPYRIGHT
2003-2025, The Open MPI Community
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