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<TITLE>MPI_Buffer_attach</TITLE>
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MPI_Buffer_attach
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Attaches a user-provided buffer for sending
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Synopsis
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int MPI_Buffer_attach(void *buffer, int size)
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Input Parameters
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buffer initial buffer address (choice)
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size buffer size, in bytes (integer)
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Notes
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The size given should be the sum of the sizes of all outstanding Bsends that
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you intend to have, plus <tt>MPI_BSEND_OVERHEAD</tt> for each Bsend that you do.
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For the purposes of calculating size, you should use <tt>MPI_Pack_size</tt>.
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In other words, in the code
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MPI_Buffer_attach(buffer, size);
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MPI_Bsend(..., count=20, datatype=type1, ...);
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...
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MPI_Bsend(..., count=40, datatype=type2, ...);
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the value of <tt>size</tt> in the <tt>MPI_Buffer_attach</tt> call should be greater than
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the value computed by
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MPI_Pack_size(20, type1, comm, &s1);
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MPI_Pack_size(40, type2, comm, &s2);
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size = s1 + s2 + 2 * MPI_BSEND_OVERHEAD;
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The <tt>MPI_BSEND_OVERHEAD</tt> gives the maximum amount of space that may be used in
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the buffer for use by the BSEND routines in using the buffer. This value
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is in <tt>mpi.h</tt> (for C) and <tt>mpif.h</tt> (for Fortran).
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Thread and Interrupt Safety
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The user is responsible for ensuring that multiple threads do not try to
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update the same MPI object from different threads. This routine should
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not be used from within a signal handler.
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The MPI standard defined a thread-safe interface but this does not
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mean that all routines may be called without any thread locks. For
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example, two threads must not attempt to change the contents of the
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same <tt>MPI_Info</tt> object concurrently. The user is responsible in this
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case for using some mechanism, such as thread locks, to ensure that
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only one thread at a time makes use of this routine.
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Because the buffer for buffered sends (e.g., <tt>MPI_Bsend</tt>) is shared by all
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threads in a process, the user is responsible for ensuring that only
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one thread at a time calls this routine or <tt>MPI_Buffer_detach</tt>.
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Notes for Fortran
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All MPI routines in Fortran (except for <tt>MPI_WTIME</tt> and <tt>MPI_WTICK</tt>) have
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an additional argument <tt>ierr</tt> at the end of the argument list. <tt>ierr
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</tt>is an integer and has the same meaning as the return value of the routine
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in C. In Fortran, MPI routines are subroutines, and are invoked with the
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<tt>call</tt> statement.
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All MPI objects (e.g., <tt>MPI_Datatype</tt>, <tt>MPI_Comm</tt>) are of type <tt>INTEGER
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</tt>in Fortran.
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Errors
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All MPI routines (except <tt>MPI_Wtime</tt> and <tt>MPI_Wtick</tt>) return an error value;
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C routines as the value of the function and Fortran routines in the last
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argument. Before the value is returned, the current MPI error handler is
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called. By default, this error handler aborts the MPI job. The error handler
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may be changed with <tt>MPI_Comm_set_errhandler</tt> (for communicators),
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<tt>MPI_File_set_errhandler</tt> (for files), and <tt>MPI_Win_set_errhandler</tt> (for
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RMA windows). The MPI-1 routine <tt>MPI_Errhandler_set</tt> may be used but
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its use is deprecated. The predefined error handler
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<tt>MPI_ERRORS_RETURN</tt> may be used to cause error values to be returned.
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Note that MPI does not guarentee that an MPI program can continue past
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an error; however, MPI implementations will attempt to continue whenever
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possible.
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MPI_SUCCESS No error; MPI routine completed successfully.
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MPI_ERR_BUFFER Invalid buffer pointer. Usually a null buffer where
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one is not valid.
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MPI_ERR_INTERN An internal error has been detected. This is fatal.
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Please send a bug report to <tt>mpi-bugs@mcs.anl.gov</tt>.
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See Also
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MPI_Buffer_detach, MPI_Bsend
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