1MPI_Comm_join(3) LAM/MPI MPI_Comm_join(3)
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6 MPI_Comm_join - Connect two MPI processed joined by a socket
7
9 #include <mpi.h>
10 int
11 MPI_Comm_join(int fd, MPI_Comm *newcomm)
12
14 fd - socket file descriptor
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18 newcomm
19 - intercommunicator with client as remote group
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23 This function only works between two LAM/MPI processes that are con‐
24 nected by a socket. They either must have the same endian orientation,
25 or not have used the homogeneous flag to mpirun (1) (-O). Both pro‐
26 cesses must be in a single LAM universe -- they must share LAM daemons
27 that are already connected to each other. That is, they were either
28 initially lamboot(1)ed together, or a lamgrow(1) command was given to
29 grow an initial LAM universe such that the resulting set includes the
30 two hosts in question.
31 The socket may not be used by the calling application until
33 MPI_Comm_join has completed. When MPI_Comm_join completes, fd may be
34 used by the calling application. Per MPI-2, the socket is only used
35 for initial handshaking -- it will not be used as the communications
36 channel between the newly connected processes.
37
40 The following code shows an abbreviated example using MPI_Comm_join
41 since no example is provided in the MPI-2 standard. Note that only one
42 rank in each MPI application should call this function since each
43 socket can only have two endpoints (i.e., an endpoint in each process).
44 Upon successful completion, the intercommunicator that is returned will
45 have two members -- the local process and the remote process.
46 MPI_Comm
48 do_join(char* server_name, int port) {
49 int sfd, fd = -1;
50 unsigned char addr[4];
51 MPI_Comm intercomm;
52 if (server_name != NULL) {
53 if (getinetaddr(server_name, &addr) == 0)
54 fd = open_socket_to_server(addr, port);
55 } else {
56 if ((sfd = open_listening_socket(&port)) >= 0) {
57 fd = accept_client_socket(sfd, -1);
58 close(sfd);
59 }
60 }
61 if (fd < 0)
62 MPI_Abort(MPI_COMM_WORLD, 0);
63 MPI_Comm_join(fd, &intercomm);
64 return intercomm;
65 }
66
70 All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have
71 an additional argument ierr at the end of the argument list. ierr is
72 an integer and has the same meaning as the return value of the routine
73 in C. In Fortran, MPI routines are subroutines, and are invoked with
74 the call statement.
75 All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in
77 Fortran.
78
81 The IMPI standard only supports MPI-1 functions. Hence, this function
82 is currently not designed to operate within an IMPI job.
83
86 If an error occurs in an MPI function, the current MPI error handler is
87 called to handle it. By default, this error handler aborts the MPI
88 job. The error handler may be changed with MPI_Errhandler_set ; the
89 predefined error handler MPI_ERRORS_RETURN may be used to cause error
90 values to be returned (in C and Fortran; this error handler is less
91 useful in with the C++ MPI bindings. The predefined error handler
92 MPI::ERRORS_THROW_EXCEPTIONS should be used in C++ if the error value
93 needs to be recovered). Note that MPI does not guarantee that an MPI
94 program can continue past an error.
95 All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error
97 value; C routines as the value of the function and Fortran routines in
98 the last argument. The C++ bindings for MPI do not return error val‐
99 ues; instead, error values are communicated by throwing exceptions of
100 type MPI::Exception (but not by default). Exceptions are only thrown
101 if the error value is not MPI::SUCCESS .
102 Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI
105 functions will return upon an error, there will be no way to recover
106 what the actual error value was.
107 MPI_SUCCESS
108 - No error; MPI routine completed successfully.
109 MPI_ERR_ARG
110 - Invalid argument. Some argument is invalid and is not identi‐
111 fied by a specific error class. This is typically a NULL
112 pointer or other such error.
113 MPI_ERR_INTERN
114 - An internal error has been detected. This is fatal. Please
115 send a bug report to the LAM mailing list (see http://www.lam-
116 mpi.org/contact.php ).
117 MPI_ERR_OTHER
118 - Other error; use MPI_Error_string to get more information
119 about this error code.
120
123 lamboot(1), lamgrow(1), mpirun(1), MPI_Finalize(3)
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127 For more information, please see the official MPI Forum web site, which
128 contains the text of both the MPI-1 and MPI-2 standards. These docu‐
129 ments contain detailed information about each MPI function (most of
130 which is not duplicated in these man pages).
131 http://www.mpi-forum.org/
133
135 join.c
136LAM/MPI 7.1.2 2/23/2006 MPI_Comm_join(3)