MPI_Sendrecv_replace(3OpenMPI) MPI_Sendrecv_replace(3OpenMPI)
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
INPUT/OUTPUT PARAMETER
buf Initial address of send and receive buffer (choice).
INPUT PARAMETERS
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 opera-tion operation
tion 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 opera-tion. operation.
tion.
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 concur-rent concurrent
rent 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
Open MPI 1.2 September 2006 MPI_Sendrecv_replace(3OpenMPI)
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