NAME

MPI_Sendrecv - Sends and receives a message.

SYNTAX

C Syntax

#include <mpi.h>
int MPI_Sendrecv(const void *sendbuf, int sendcount, MPI_Datatype sendtype,
	int dest, int sendtag, void *recvbuf, int recvcount,
	MPI_Datatype recvtype, int source, int recvtag,
	MPI_Comm comm, MPI_Status *status)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_SENDRECV(SENDBUF, SENDCOUNT, SENDTYPE, DEST, SENDTAG,
		RECVBUF, RECVCOUNT, RECVTYPE, SOURCE, RECVTAG, COMM,
		STATUS, IERROR)
	<type>	SENDBUF(*), RECVBUF(*)
	INTEGER	SENDCOUNT, SENDTYPE, DEST, SENDTAG
	INTEGER	RECVCOUNT, RECVTYPE, SOURCE, RECVTAG, COMM
	INTEGER	STATUS(MPI_STATUS_SIZE), IERROR

Fortran 2008 Syntax

USE mpi_f08
MPI_Sendrecv(sendbuf, sendcount, sendtype, dest, sendtag, recvbuf,
		recvcount, recvtype, source, recvtag, comm, status, ierror)
	TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
	TYPE(*), DIMENSION(..) :: recvbuf
	INTEGER, INTENT(IN) :: sendcount, dest, sendtag, recvcount, source,
	recvtag
	TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
	TYPE(MPI_Comm), INTENT(IN) :: comm
	TYPE(MPI_Status) :: status
	INTEGER, OPTIONAL, INTENT(OUT) :: ierror

C++ Syntax

#include <mpi.h>
void Comm::Sendrecv(const void *sendbuf, int sendcount, const
	Datatype& sendtype, int dest, int sendtag, void *recvbuf,
	int recvcount, const Datatype& recvtype, int source,
	int recvtag, Status& status) const
void Comm::Sendrecv(const void *sendbuf, int sendcount, const
	Datatype& sendtype, int dest, int sendtag, void *recvbuf,
	int recvcount, const Datatype& recvtype, int source,
	int recvtag) const

INPUT PARAMETERS

sendbuf: Initial address of send buffer (choice).
sendcount: Number of elements to send (integer).
sendtype: Type of elements in send buffer (handle).
dest: Rank of destination (integer).
sendtag: Send tag (integer).
recvcount: Maximum number of elements to receive (integer).
recvtype: Type of elements in receive buffer (handle).
source: Rank of source (integer).
recvtag: Receive tag (integer).
comm: Communicator (handle).

OUTPUT PARAMETERS

recvbuf: Initial address of receive buffer (choice).
status: Status object (status). This refers to the receive operation.
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-1 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 executes a blocking send and receive operation. Both send and receive use the same communicator, but possibly different tags. The send buffer and receive buffers must be disjoint, and may have different lengths and datatypes.

If your application does not need to examine the status field, you can save resources by using the predefined constant MPI_STATUS_IGNORE as a special value for the status argument.

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.