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 very 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) so as 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 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(sendbuf, sendcount, sendtype, dest, sendtag, recvbuf, recvcount, recvtype, source, recvtag, comm, status) | |
| IN sendbuf | initial address of send buffer (choice) |
| IN sendcount | number of elements in send buffer (non-negative integer) |
| IN sendtype | type of elements in send buffer (handle) |
| IN dest | rank of destination (integer) |
| IN sendtag | send tag (integer) |
| OUT recvbuf | initial address of receive buffer (choice) |
| IN recvcount | number of elements in receive buffer (non-negative integer) |
| IN recvtype | type of elements in receive buffer (handle) |
| IN source | rank of source or MPI_ANY_SOURCE (integer) |
| IN recvtag | receive tag or MPI_ANY_TAG (integer) |
| IN comm | communicator (handle) |
| OUT status | status object (Status) |
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)
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
MPI_SENDRECV(SENDBUF, SENDCOUNT, SENDTYPE, DEST, SENDTAG, RECVBUF, RECVCOUNT, RECVTYPE, SOURCE, RECVTAG, COMM, STATUS, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNT, SENDTYPE, DEST, SENDTAG, RECVCOUNT, RECVTYPE,
SOURCE, RECVTAG, COMM, STATUS(MPI_STATUS_SIZE), IERROR
Execute 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.
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.
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)
MPI_Sendrecv_replace(buf, count, datatype, dest, sendtag, source, recvtag, comm, status, ierror)
TYPE(*), DIMENSION(..) :: buf
INTEGER, INTENT(IN) :: count, dest, sendtag, source, recvtag
TYPE(MPI_Datatype), INTENT(IN) :: datatype
TYPE(MPI_Comm), INTENT(IN) :: comm
TYPE(MPI_Status) :: status
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_SENDRECV_REPLACE(BUF, COUNT, DATATYPE, DEST, SENDTAG, SOURCE, RECVTAG, COMM, STATUS, IERROR)
<type> BUF(*)
INTEGER COUNT, DATATYPE, DEST, SENDTAG, SOURCE, RECVTAG, COMM,
STATUS(MPI_STATUS_SIZE), IERROR
Execute 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.
Advice
to implementors.
Additional intermediate buffering is needed for the
``replace'' variant.
( End of advice to implementors.)