4.2.7. Blocking Send-Receive
Up: Blocking Send and Receive Operations
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The send-receive operations combine in one operation the sending of a
message to one destination and the receiving of another message, from
another MPI 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
MPI processes. If blocking sends and receives are used for such a shift,
then one needs to order the sends and receives correctly (for
example, MPI processes with even rank in the communicator
send, then receive, MPI processes with odd rank in the communicator 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 procedures described in Chapter Virtual Topologies for MPI Processes 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 receive buffer element (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) |
C binding
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)
int MPI_Sendrecv_c(const void *sendbuf, MPI_Count sendcount, MPI_Datatype sendtype, int dest, int sendtag, void *recvbuf, MPI_Count recvcount, MPI_Datatype recvtype, int source, int recvtag, MPI_Comm comm, MPI_Status *status)
Fortran 2008 binding
MPI_Sendrecv(sendbuf, sendcount, sendtype, dest, sendtag, recvbuf, recvcount, recvtype, source, recvtag, comm, status, ierror)
TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
INTEGER, INTENT(IN) :: sendcount, dest, sendtag, recvcount, source, recvtag
TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
TYPE(*), DIMENSION(..) :: recvbuf
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) !(_c)
TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
INTEGER(KIND=MPI_COUNT_KIND), INTENT(IN) :: sendcount, recvcount
TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
INTEGER, INTENT(IN) :: dest, sendtag, source, recvtag
TYPE(*), DIMENSION(..) :: recvbuf
TYPE(MPI_Comm), INTENT(IN) :: comm
TYPE(MPI_Status) :: status
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
Fortran binding
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-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.
| MPI_SENDRECV_REPLACE(buf, count, datatype, dest, sendtag, source, recvtag, comm, status) |
| INOUT buf | initial address of send and receive buffer (choice) |
| IN count | number of elements in send and receive buffer (non-negative integer) |
| IN datatype | type of elements in send and receive buffer (handle) |
| IN dest | rank of destination (integer) |
| IN sendtag | send message tag (integer) |
| IN source | rank of source or MPI_ANY_SOURCE (integer) |
| IN recvtag | receive message tag or MPI_ANY_TAG (integer) |
| IN comm | communicator (handle) |
| OUT status | status object (status) |
C binding
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)
int MPI_Sendrecv_replace_c(void *buf, MPI_Count count, MPI_Datatype datatype, int dest, int sendtag, int source, int recvtag, MPI_Comm comm, MPI_Status *status)
Fortran 2008 binding
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) !(_c)
TYPE(*), DIMENSION(..) :: buf
INTEGER(KIND=MPI_COUNT_KIND), INTENT(IN) :: count
TYPE(MPI_Datatype), INTENT(IN) :: datatype
INTEGER, INTENT(IN) :: dest, sendtag, source, recvtag
TYPE(MPI_Comm), INTENT(IN) :: comm
TYPE(MPI_Status) :: status
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
Fortran binding
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.)
Up: Blocking Send and Receive Operations
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