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.TH "MPI_SENDRECV_REPLACE" "3" "Apr 08, 2024" "" "Open MPI"
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.sp
\fI\%MPI_Sendrecv_replace\fP — Sends and receives a message using a single
buffer.
.SH SYNTAX
.SS C Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
#include <mpi.h>

int MPI_Sendrecv_replace(void *buf, int count, MPI_Datatype datatype,
     int dest, int sendtag, int source, int recvtag, MPI_Comm comm,
     MPI_Status *status)
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
USE MPI
! or the older form: INCLUDE \(aqmpif.h\(aq
MPI_SENDRECV_REPLACE(BUF, COUNT, DATATYPE, DEST, SENDTAG, SOURCE,
             RECVTAG, COMM, STATUS, IERROR)
     <type>  BUF(*)
     INTEGER COUNT, DATATYPE, DEST, SENDTAG
     INTEGER SOURCE, RECVTAG, COMM
     INTEGER STATUS(MPI_STATUS_SIZE), IERROR
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran 2008 Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
USE mpi_f08
MPI_Sendrecv_replace(buf, count, datatype, dest, sendtag, source, recvtag,
             comm, status, ierror)
     TYPE(*), DIMENSION(..) :: buf
     INTEGER, INTENT(IN) :: count, dest, sendtag, source, recvtag
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     TYPE(MPI_Comm), INTENT(IN) :: comm
     TYPE(MPI_Status) :: status
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
.ft P
.fi
.UNINDENT
.UNINDENT
.SH INPUT/OUTPUT PARAMETER
.INDENT 0.0
.IP \(bu 2
\fBbuf\fP: Initial address of send and receive buffer (choice).
.UNINDENT
.SH INPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBcount\fP: Number of elements in send and receive buffer (integer).
.IP \(bu 2
\fBdatatype\fP: Type of elements to send and receive (handle).
.IP \(bu 2
\fBdest\fP: Rank of destination (integer).
.IP \(bu 2
\fBsendtag\fP: Send message tag (integer).
.IP \(bu 2
\fBsource\fP: Rank of source (integer).
.IP \(bu 2
\fBrecvtag\fP: Receive message tag (integer).
.IP \(bu 2
\fBcomm\fP: Communicator (handle).
.UNINDENT
.SH OUTPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBstatus\fP: Status object (status).
.IP \(bu 2
\fBierror\fP: Fortran only: Error status (integer).
.UNINDENT
.SH DESCRIPTION
.sp
The send\-receive operations combine in one call the sending of a message
to one destination and the receiving of another message, from another
process. The two (source and destination) are possibly the same. A
send\-receive operation is useful for executing a shift operation across
a chain of processes. If blocking sends and receives are used for such a
shift, then one needs to order the sends and receives correctly (for
example, even processes send, then receive; odd processes receive first,
then send) in order to prevent cyclic dependencies that may lead to
deadlock. When a send\-receive operation is used, the communication
subsystem takes care of these issues. The send\-receive operation can be
used in conjunction with the functions described in Chapter 6 of the MPI
Standard, “Process Topologies,” in order to perform shifts on various
logical topologies. Also, a send\-receive operation is useful for
implementing remote procedure calls.
.sp
A message sent by a send\-receive operation can be received by a regular
receive operation or probed by a probe operation; a send\-receive
operation can receive a message sent by a regular send operation.
.sp
\fI\%MPI_Sendrecv_replace\fP executes a blocking send and receive. The same
buffer is used both for the send and for the receive, so that the
message sent is replaced by the message received.
.sp
The semantics of a send\-receive operation is what would be obtained if
the caller forked two concurrent threads, one to execute the send, and
one to execute the receive, followed by a join of these two threads.
.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:
.INDENT 0.0
.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.
.UNINDENT
.sp
MPI applications can also implement their own error handlers by calling:
.INDENT 0.0
.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
.UNINDENT
.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 messages received
by \fI\%MPI_Sendrecv_replace\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_Sendrecv_replace\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
.INDENT 0.0
.IP \(bu 2
\fI\%MPI_Sendrecv\fP
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.SH COPYRIGHT
2003-2024, The Open MPI Community
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