Skip to content

Latest commit

 

History

History
131 lines (99 loc) · 4.36 KB

MPI_Sendrecv.3.rst

File metadata and controls

131 lines (99 loc) · 4.36 KB
Raw

MPI_Sendrecv

:ref:`MPI_Sendrecv` |mdash| 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

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 the "Process Topologies" chapter in the MPI Standard 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.

:ref:`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

Note that per the "Return Status" section in the "Point-to-Point Communication" chapter in the MPI Standard, MPI errors on messages received by :ref:`MPI_Sendrecv` 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 :ref:`MPI_Sendrecv` if the back-end error handler returns it. The pre-defined MPI error handler MPI_ERRORS_RETURN exhibits this behavior, for example.

.. seealso::
   * :ref:`MPI_Sendrecv_replace`