MPI_Sendrecv_replace(3)

NAME
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
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

C++ Syntax
#include <mpi.h>
void Comm::Sendrecv_replace(void* buf, int count, const
	Datatype& datatype, int dest, int sendtag, int source,
	int recvtag, Status& status) const

void Comm::Sendrecv_replace(void* buf, int count, const
	Datatype& datatype, int dest, int sendtag, int source,
	int recvtag) const

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 value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.

Before the error value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.

SEE ALSO

MPI_Sendrecv