1MPIL_Comm_id(3) LAM/MPI MPIL_Comm_id(3)
2
6 MPIL_Comm_id - LAM/MPI-specific function to return the context ID of
7 the communicator
8
10 #include <mpi.h>
11 int
12 MPIL_Comm_id(MPI_Comm comm, int *pcid)
13
15 comm - communicator (handle)
16
19 pcid - communicator context id (integer)
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23 In the LAM implementation of MPI, each communicator has an integer con‐
24 text ID associated with it for synchronizing on different contexts.
25 This ID is global to all the processes in the communicator's group, and
26 uniquely identifies that communicator for each process. These proper‐
27 ties allow the processes to safely exchange messages without interfer‐
28 ence from operations on other communicators.
29 The MPI standard does not provide a way to access/view this implementa‐
31 tion-dependent synchronization since communicators are opaque objects.
32 Users do not need such access for normal MPI operations. On the other
33 hand, when debugging MPI applications, the opaque nature of communica‐
34 tors hinders the user's efforts. This is especially true on fully
35 observable systems such as LAM, where users can monitor the full state
36 of the processes and message queues, which includes the context ID (see
37 mpitask (1) and mpimsg (1)).
38 This is a LAM/MPI-specific function and is intended mainly for debug‐
40 ging. If this function is used, it should be used in conjunction with
41 the LAM_MPI C preprocessor macro
42 #if LAM_MPI
44 int cid;
45 MPIL_Comm_id(MPI_COMM_WORLD, &cid);
46 #endif
47
51 All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have
52 an additional argument ierr at the end of the argument list. ierr is
53 an integer and has the same meaning as the return value of the routine
54 in C. In Fortran, MPI routines are subroutines, and are invoked with
55 the call statement.
56 All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in
58 Fortran.
59
62 If an error occurs in an MPI function, the current MPI error handler is
63 called to handle it. By default, this error handler aborts the MPI
64 job. The error handler may be changed with MPI_Errhandler_set ; the
65 predefined error handler MPI_ERRORS_RETURN may be used to cause error
66 values to be returned (in C and Fortran; this error handler is less
67 useful in with the C++ MPI bindings. The predefined error handler
68 MPI::ERRORS_THROW_EXCEPTIONS should be used in C++ if the error value
69 needs to be recovered). Note that MPI does not guarantee that an MPI
70 program can continue past an error.
71 All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error
73 value; C routines as the value of the function and Fortran routines in
74 the last argument. The C++ bindings for MPI do not return error val‐
75 ues; instead, error values are communicated by throwing exceptions of
76 type MPI::Exception (but not by default). Exceptions are only thrown
77 if the error value is not MPI::SUCCESS .
78 Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI
81 functions will return upon an error, there will be no way to recover
82 what the actual error value was.
83 MPI_SUCCESS
84 - No error; MPI routine completed successfully.
85 MPI_ERR_COMM
86 - Invalid communicator. A common error is to use a null commu‐
87 nicator in a call (not even allowed in MPI_Comm_rank ).
88 MPI_ERR_ARG
89 - Invalid argument. Some argument is invalid and is not identi‐
90 fied by a specific error class. This is typically a NULL
91 pointer or other such error.
92
95 MPIL_Comm_gps, MPIL_Type_id
96
98 mpil_id.c
99LAM/MPI 7.1.2 2/23/2006 MPIL_Comm_id(3)