MPI_Sendrecv(3OpenMPI)

NAME
MPI_Sendrecv - Sends and receives a message.

SYNTAX

C Syntax
#include <mpi.h>
int MPI_Sendrecv(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
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

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.

SEE ALSO

MPI_Sendrecv_replace