NAME¶
MPI_Sendrecv_replace - Sends and receives a message using a single
buffer.
SYNTAX¶
C Syntax¶
#include <mpi.h>
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)
Fortran Syntax¶
INCLUDE 'mpif.h'
MPI_SENDRECV_REPLACE( BUF, COUNT, DATATYPE, DEST, SENDTAG, SOURCE,
RECVTAG, COMM, STATUS, IERROR)
<type> BUF(*)
INTEGER COUNT, DATATYPE, DEST, SENDTAG
INTEGER SOURCE, RECVTAG, COMM
INTEGER STATUS(MPI_STATUS_SIZE), IERROR
C++ Syntax¶
#include <mpi.h>
void Comm::Sendrecv_replace(void* buf, int count, const
Datatype& datatype, int dest, int sendtag, int source,
int recvtag, Status& status) const
void Comm::Sendrecv_replace(void* buf, int count, const
Datatype& datatype, int dest, int sendtag, int source,
int recvtag) const
- buf
- Initial address of send and receive buffer (choice).
- count
- Number of elements in send and receive buffer (integer).
- datatype
- Type of elements to send and receive (handle).
- dest
- Rank of destination (integer).
- sendtag
- Send message tag (integer).
- source
- Rank of source (integer).
- recvtag
- Receive message tag (integer).
- comm
- Communicator (handle).
OUTPUT PARAMETERS¶
- status
- Status object (status).
- 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 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_replace executes 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.
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.
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