1MPI_Barrier(3) LAM/MPI MPI_Barrier(3)
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6 MPI_Barrier - Blocks until all process have reached this routine.
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9 #include <mpi.h>
10 int MPI_Barrier(MPI_Comm comm)
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13 comm - communicator (handle)
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17 Blocks the caller until all group members have called it; the call
18 returns at any process only after all group members have entered the
19 call.
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23 This function has had the IMPI extensions implemented. It is legal to
24 call this function on IMPI communicators.
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28 For 4 or less ranks, a linear algorithm is used, where rank 0 first
29 receives synchronization message from each other rank. Rank 0 then
30 sends out a synchronization message to each other rank.
31 If more than 4 ranks are involved, a tree-based algorithm is used to
33 receive and then send the synchronization messages to and from rank 0.
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37 All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have
38 an additional argument ierr at the end of the argument list. ierr is
39 an integer and has the same meaning as the return value of the routine
40 in C. In Fortran, MPI routines are subroutines, and are invoked with
41 the call statement.
42 All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in
44 Fortran.
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48 If an error occurs in an MPI function, the current MPI error handler is
49 called to handle it. By default, this error handler aborts the MPI
50 job. The error handler may be changed with MPI_Errhandler_set ; the
51 predefined error handler MPI_ERRORS_RETURN may be used to cause error
52 values to be returned (in C and Fortran; this error handler is less
53 useful in with the C++ MPI bindings. The predefined error handler
54 MPI::ERRORS_THROW_EXCEPTIONS should be used in C++ if the error value
55 needs to be recovered). Note that MPI does not guarantee that an MPI
56 program can continue past an error.
57 All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error
59 value; C routines as the value of the function and Fortran routines in
60 the last argument. The C++ bindings for MPI do not return error val‐
61 ues; instead, error values are communicated by throwing exceptions of
62 type MPI::Exception (but not by default). Exceptions are only thrown
63 if the error value is not MPI::SUCCESS .
64 Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI
67 functions will return upon an error, there will be no way to recover
68 what the actual error value was.
69 MPI_SUCCESS
70 - No error; MPI routine completed successfully.
71 MPI_ERR_COMM
72 - Invalid communicator. A common error is to use a null commu‐
73 nicator in a call (not even allowed in MPI_Comm_rank ).
74 MPI_ERR_OTHER
75 - A collective implementation was not able to be located at run-
76 time for this communicator.
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80 For more information, please see the official MPI Forum web site, which
81 contains the text of both the MPI-1 and MPI-2 standards. These docu‐
82 ments contain detailed information about each MPI function (most of
83 which is not duplicated in these man pages).
84 http://www.mpi-forum.org/
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90 The LAM Team would like the thank the MPICH Team for the handy program
91 to generate man pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sow‐
92 ing/sowing.tar.gz ), the initial formatting, and some initial text for
93 most of the MPI-1 man pages.
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96 barrier.c
97LAM/MPI 7.1.2 2/23/2006 MPI_Barrier(3)