190 lines
4.4 KiB
Groff
190 lines
4.4 KiB
Groff
.TH MPI_Buffer_detach 3 "2/3/2025" " " "MPI"
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.SH NAME
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MPI_Buffer_detach \- Removes an existing buffer (for use in MPI_Bsend etc)
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.SH SYNOPSIS
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.nf
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.fi
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.nf
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int MPI_Buffer_detach(void *buffer_addr, int *size)
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.fi
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.nf
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int MPI_Buffer_detach_c(void *buffer_addr, MPI_Count *size)
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.fi
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.SH OUTPUT PARAMETERS
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.PD 0
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.TP
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.B buffer_addr
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- initial buffer address (choice)
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.PD 1
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.PD 0
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.TP
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.B size
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- buffer size, in bytes (integer)
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.PD 1
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.SH NOTES
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The reason that
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.I MPI_Buffer_detach
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returns the address and size of the
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buffer being detached is to allow nested libraries to replace and restore
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the buffer. For example, consider
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.nf
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int size, mysize, idummy;
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void *ptr, *myptr, *dummy;
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MPI_Buffer_detach(&ptr, &size);
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MPI_Buffer_attach(myptr, mysize);
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\&.
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\&.
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\&.
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\&.
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\&.
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\&.
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library code ...
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\&.
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\&.
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\&.
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MPI_Buffer_detach(&dummy, &idummy);
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MPI_Buffer_attach(ptr, size);
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.fi
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This is much like the action of the Unix signal routine and has the same
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strengths (it is simple) and weaknesses (it only works for nested usages).
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Note that for this approach to work, MPI_Buffer_detach must return MPI_SUCCESS
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even when there is no buffer to detach. In that case, it returns a size of
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zero. The MPI 1.1 standard for
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.I MPI_BUFFER_DETACH
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contains the text
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.nf
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The statements made in this section describe the behavior of MPI for
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buffered-mode sends. When no buffer is currently associated, MPI behaves
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as if a zero-sized buffer is associated with the process.
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.fi
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This could be read as applying only to the various Bsend routines. This
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implementation takes the position that this applies to
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.I MPI_BUFFER_DETACH
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as well.
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.SH 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
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.I MPI_Info
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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.,
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.I MPI_Bsend
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) 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
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.I MPI_Buffer_attach
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\&.
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.SH NOTES FOR FORTRAN
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All MPI routines in Fortran (except for
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.I MPI_WTIME
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and
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.I MPI_WTICK
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) have
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an additional argument
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.I ierr
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at the end of the argument list.
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.I ierr
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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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.I call
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statement.
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All MPI objects (e.g.,
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.I MPI_Datatype
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,
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.I MPI_Comm
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) are of type
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.I INTEGER
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in Fortran.
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The Fortran binding for this routine is different. Because Fortran
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does not have pointers, it is impossible to provide a way to use the
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output of this routine to exchange buffers. In this case, only the
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size field is set.
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.SH NOTES FOR C
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Even though the
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.I bufferptr
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argument is declared as
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.I void *
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, it is
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really the address of a void pointer. See the rationale in the
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standard for more details.
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.SH ERRORS
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All MPI routines (except
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.I MPI_Wtime
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and
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.I MPI_Wtick
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) 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
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.I MPI_Comm_set_errhandler
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(for communicators),
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.I MPI_File_set_errhandler
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(for files), and
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.I MPI_Win_set_errhandler
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(for
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RMA windows). The MPI-1 routine
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.I MPI_Errhandler_set
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may be used but
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its use is deprecated. The predefined error handler
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.I MPI_ERRORS_RETURN
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may be used to cause error values to be returned.
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Note that MPI does
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.B not
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guarantee 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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.PD 0
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.TP
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.B MPI_SUCCESS
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- No error; MPI routine completed successfully.
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.PD 1
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.PD 0
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.TP
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.B MPI_ERR_ARG
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- Invalid argument. Some argument is invalid and is not
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identified by a specific error class (e.g.,
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.I MPI_ERR_RANK
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).
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.PD 1
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.PD 0
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.TP
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.B MPI_ERR_OTHER
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- Other error; use
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.I MPI_Error_string
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to get more information
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about this error code.
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.PD 1
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.SH SEE ALSO
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MPI_Buffer_attach
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.br
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