NAME
MPI_Comm_join - Connect two MPI processed joined by a socket
SYNOPSIS
#include <mpi.h>
int
MPI_Comm_join(int fd, MPI_Comm *newcomm)
INPUT PARAMETER
fd - socket file descriptor
OUTPUT PARAMETER
newcomm
- intercommunicator with client as remote group
DESCRIPTION
This function only works between two LAM/MPI processes that are
connected by a socket. They either must have the same endian
orientation, or not have used the homogeneous flag to mpirun (1) (-O).
Both processes must be in a single LAM universe -- they must share LAM
daemons that are already connected to each other. That is, they were
either initially lamboot(1)ed together, or a lamgrow(1) command was
given to grow an initial LAM universe such that the resulting set
includes the two hosts in question.
The socket may not be used by the calling application until
MPI_Comm_join has completed. When MPI_Comm_join completes, fd may be
used by the calling application. Per MPI-2, the socket is only used
for initial handshaking -- it will not be used as the communications
channel between the newly connected processes.
SAMPLE
The following code shows an abbreviated example using MPI_Comm_join
since no example is provided in the MPI-2 standard. Note that only one
rank in each MPI application should call this function since each
socket can only have two endpoints (i.e., an endpoint in each process).
Upon successful completion, the intercommunicator that is returned will
have two members -- the local process and the remote process.
MPI_Comm
do_join(char* server_name, int port) {
int sfd, fd = -1;
unsigned char addr[4];
MPI_Comm intercomm;
if (server_name != NULL) {
if (getinetaddr(server_name, &addr) == 0)
fd = open_socket_to_server(addr, port);
} else {
if ((sfd = open_listening_socket(&port)) >= 0) {
fd = accept_client_socket(sfd, -1);
close(sfd);
}
}
if (fd < 0)
MPI_Abort(MPI_COMM_WORLD, 0);
MPI_Comm_join(fd, &intercomm);
return intercomm;
}
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.
USAGE WITH IMPI EXTENSIONS
The IMPI standard only supports MPI-1 functions. Hence, this function
is currently not designed to operate within an IMPI job.
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_ARG
- Invalid argument. Some argument is invalid and is not
identified by a specific error class. This is typically a NULL
pointer or other such error.
MPI_ERR_INTERN
- An internal error has been detected. This is fatal. Please
send a bug report to the LAM mailing list (see http://www.lam-
mpi.org/contact.php ).
MPI_ERR_OTHER
- Other error; use MPI_Error_string to get more information
about this error code.
SEE ALSO
lamboot(1), lamgrow(1), mpirun(1), MPI_Finalize(3)
MORE INFORMATION
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/
LOCATION
join.c