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)
- 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)
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