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.TH "MPI_COMM_SET_ATTR" "3" "May 30, 2025" "" "Open MPI"
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\fI\%MPI_Comm_set_attr\fP — Stores attribute value associated with a key.
.SH SYNTAX
.SS C Syntax
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.INDENT 3.5
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.nf
.ft C
#include <mpi.h>

int MPI_Comm_set_attr(MPI_Comm comm, int comm_keyval, void *attribute_val)
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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_COMM_SET_ATTR(COMM, COMM_KEYVAL, ATTRIBUTE_VAL, IERROR)
     INTEGER COMM, COMM_KEYVAL, IERROR
     INTEGER(KIND=MPI_ADDRESS_KIND) ATTRIBUTE_VAL
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.SS Fortran 2008 Syntax
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.INDENT 3.5
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.ft C
USE mpi_f08
MPI_Comm_set_attr(comm, comm_keyval, attribute_val, ierror)
     TYPE(MPI_Comm), INTENT(IN) :: comm
     INTEGER, INTENT(IN) :: comm_keyval
     INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: attribute_val
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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.SH INPUT/OUTPUT PARAMETER
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.IP \(bu 2
\fBcomm\fP: Communicator from which attribute will be attached (handle).
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.SH INPUT PARAMETERS
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.IP \(bu 2
\fBcomm_keyval\fP: Key value (integer).
.IP \(bu 2
\fBattribute_val\fP: Attribute value.
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.SH OUTPUT PARAMETER
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.IP \(bu 2
\fBierror\fP: Fortran only: Error status (integer).
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.SH DESCRIPTION
.sp
\fI\%MPI_Comm_set_attr\fP stores the stipulated attribute value \fIattribute_val\fP
for subsequent retrieval by \fI\%MPI_Comm_get_attr\fP\&. If the value is already
present, then the outcome is as if \fI\%MPI_Comm_delete_attr\fP was first called
to delete the previous value (and the callback function \fBdelete_fn\fP was
executed), and a new value was next stored. The call is erroneous if
there is no key with value \fIcomm_keyval\fP; in particular
\fBMPI_KEYVAL_INVALID\fP is an erroneous key value. The call will fail if the
delete_fn function returned an error code other than \fBMPI_SUCCESS\fP\&.
.sp
This function replaces \fI\%MPI_Attr_put\fP, the use of which is deprecated. The
C binding is identical. The Fortran binding differs in that
\fIattribute_val\fP is an address\-sized integer.
.SH NOTES
.sp
Values of the permanent attributes \fBMPI_TAG_UB\fP, \fBMPI_HOST\fP, \fBMPI_IO\fP, and
\fBMPI_WTIME_IS_GLOBAL\fP may not be changed.
.sp
The type of the attribute value depends on whether C or Fortran is being
used. In C, an attribute value is a pointer (\fBvoid *\fP); in Fortran, it is
a single, address\-size integer system for which a pointer does not fit
in an integer.
.sp
If an attribute is already present, the delete function (specified when
the corresponding keyval was created) will be called.
.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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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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Note that MPI does not guarantee that an MPI program can continue past
an error.
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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.
.SH COPYRIGHT
2003-2025, The Open MPI Community
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