:ref:`MPI_Sendrecv` |mdash| Sends and receives a message.
#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)
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
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
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).
recvbuf
: Initial address of receive buffer (choice).status
: Status object (status). This refers to the receive operation.ierror
: Fortran only: Error status (integer).
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.
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`