MPI_SENDRECV_REPLACE(3)				     Open MPI				   MPI_SENDRECV_REPLACE(3)

MPI_Sendrecv_replace — Sends and receives a message using a single buffer.

SYNTAX
   C Syntax
	  #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)

   Fortran Syntax
	  USE MPI
	  ! or the older form: INCLUDE 'mpif.h'
	  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

   Fortran 2008 Syntax
	  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

INPUT/OUTPUT PARAMETER
       • buf: Initial address of send and receive buffer (choice).

INPUT PARAMETERS
       • count: Number of elements in send and receive buffer (integer).

       • datatype: Type of elements to send and receive (handle).

       • dest: Rank of destination (integer).

       • sendtag: Send message tag (integer).

       • source: Rank of source (integer).

       • recvtag: Receive message tag (integer).

       • comm: Communicator (handle).

OUTPUT PARAMETERS
       • status: Status object (status).

       • ierror: Fortran only: Error status (integer).

DESCRIPTION
       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.

       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.

       MPI_Sendrecv_replace 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.

       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.

ERRORS
       Almost all MPI routines return an error value; C routines as the return result of the function and  Fortran
       routines in the last argument.

       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	MPI_Init  <#mpi-init>/MPI_Init_thread  <#mpi-init-thread>,
       after  MPI_Finalize  <#mpi-finalize>,  or  when	using the Sessions Model exclusively) the error raises the
       initial error handler. The initial error handler can  be	 changed  by  calling  MPI_Comm_set_errhandler	<#
       mpi-comm-set-errhandler>	 on  MPI_COMM_SELF  when  using the World model, or the mpi_initial_errhandler CLI
       argument	 to  mpiexec  or  info	key   to   MPI_Comm_spawn   <#mpi-comm-spawn>/MPI_Comm_spawn_multiple	<#
       mpi-comm-spawn-multiple>.   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.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT  An  error handler that can be invoked on a communicator, window, file, or session. When
	 called on a communicator, it acts as if MPI_Abort <#mpi-abort> was called on that communicator. If called
	 on a window or file, acts as if MPI_Abort <#mpi-abort> 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.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler	 <#mpi-comm-create-errhandler>	   then	    MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	<#mpi-file-create-errhandler>	  then	   MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

       See the Error Handling section of the MPI-3.1 standard for more information.

       Note that per the “Return Status” section in the “Point-to-Point Communication” chapter in the MPI Standard
       <https://www.mpi-forum.org/docs/>,  MPI	errors on messages received by MPI_Sendrecv_replace do not set the
       status.MPI_ERROR field in the returned status.  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 MPI_Sendrecv_replace if the
       back-end error handler returns it.  The pre-defined  MPI	 error	handler	 MPI_ERRORS_RETURN  exhibits  this
       behavior, for example.

       See also:

	  • MPI_Sendrecv <#mpi-sendrecv>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				   MPI_SENDRECV_REPLACE(3)
