NAME¶
MPI_Sendrecv_replace - Sends and receives using a single buffer
SYNOPSIS¶
#include <mpi.h>
int MPI_Sendrecv_replace(void *buf, int count,
MPI_Datatype dtype, int dest, int stag,
int src, int rtag, MPI_Comm comm,
MPI_Status *status)
- count
- - number of elements in send and receive buffer (integer)
- dtype
- - type of elements in send and receive buffer (handle)
- dest
- - rank of destination (integer)
- stag
- - send message tag (integer)
- src
- - rank of source (integer)
- rtag
- - receive message tag (integer)
- comm
- - communicator (handle)
OUTPUT PARAMETERS¶
- buf
- - initial address of send and receive buffer (choice)
- status
- - status object (Status)
NOTES¶
To dispell a common misconception:
src and
dest do not have to be
the same. Additionally, a common mistake when using this function is to
mismatch the tags with the source and destination ranks, which can result in
deadlock.
This function is guaranteed not to deadlock in situations where pairs of
blocking sends and receives may deadlock. For example, the following code may
deadlock if all ranks in
MPI_COMM_WORLD execute it simultaneously
int rank, size, to, from;
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &size);
to = (rank + 1) % size;
from = (rank + size - 1) % size;
MPI_Send(send_buffer, ..., to, tag, MPI_COMM_WORLD);
MPI_Recv(recv_buffer, ..., from, tag, MPI_COMM_WORLD);
If even one rank's
MPI_Send blocks and never completes, the entire
operation may deadlock. One alternative is to use
MPI_Sendrecv in this
situation because it is guaranteed not to deadlock.
NOTES FOR FORTRAN¶
All MPI routines in Fortran (except for
MPI_WTIME and
MPI_WTICK )
have an additional argument
ierr at the end of the argument list.
ierr is an integer and has the same meaning as the return value of the
routine in C. In Fortran, MPI routines are subroutines, and are invoked with
the
call statement.
All MPI objects (e.g.,
MPI_Datatype ,
MPI_Comm ) are of type
INTEGER in Fortran.
ERRORS¶
If an error occurs in an MPI function, the current MPI error handler is called
to handle it. By default, this error handler aborts the MPI job. The error
handler may be changed with
MPI_Errhandler_set ; the predefined error
handler
MPI_ERRORS_RETURN may be used to cause error values to be
returned (in C and Fortran; this error handler is less useful in with the C++
MPI bindings. The predefined error handler
MPI::ERRORS_THROW_EXCEPTIONS
should be used in C++ if the error value needs to be recovered). Note that MPI
does
not guarantee that an MPI program can continue past an error.
All MPI routines (except
MPI_Wtime and
MPI_Wtick ) return an error
value; C routines as the value of the function and Fortran routines in the
last argument. The C++ bindings for MPI do not return error values; instead,
error values are communicated by throwing exceptions of type
MPI::Exception (but not by default). Exceptions are only thrown if the
error value is not
MPI::SUCCESS .
Note that if the
MPI::ERRORS_RETURN handler is set in C++, while MPI
functions will return upon an error, there will be no way to recover what the
actual error value was.
- MPI_SUCCESS
- - No error; MPI routine completed successfully.
- MPI_ERR_COMM
- - Invalid communicator. A common error is to use a null communicator in a
call (not even allowed in MPI_Comm_rank ).
- MPI_ERR_COUNT
- - Invalid count argument. Count arguments must be non-negative; a count of
zero is often valid.
- MPI_ERR_TYPE
- - Invalid datatype argument. May be an uncommitted MPI_Datatype (see
MPI_Type_commit ).
- MPI_ERR_TAG
- - Invalid tag argument. Tags must be non-negative; tags in a receive (
MPI_Recv , MPI_Irecv , MPI_Sendrecv , etc.) may also
be MPI_ANY_TAG . The largest tag value is available through the the
attribute MPI_TAG_UB .
- MPI_ERR_RANK
- - Invalid source or destination rank. Ranks must be between zero and the
size of the communicator minus one; ranks in a receive ( MPI_Recv ,
MPI_Irecv , MPI_Sendrecv , etc.) may also be
MPI_ANY_SOURCE .
- MPI_ERR_TRUNCATE
- - Message truncated on receive. The buffer size specified was too small
for the received message. This is a recoverable error in the LAM/MPI
implementation.
- MPI_ERR_OTHER
- - This error is returned when some part of the LAM/MPI implementation is
unable to acquire memory.
SEE ALSO¶
MPI_Sendrecv
For more information, please see the official MPI Forum web site, which contains
the text of both the MPI-1 and MPI-2 standards. These documents contain
detailed information about each MPI function (most of which is not duplicated
in these man pages).
http://www.mpi-forum.org/
ACKNOWLEDGEMENTS¶
The LAM Team would like the thank the MPICH Team for the handy program to
generate man pages ("doctext" from
ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz ), the initial
formatting, and some initial text for most of the MPI-1 man pages.
LOCATION¶
sendrecvrep.c