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MPI_Buffer_detach(3) MPI MPI_Buffer_detach(3) NAME MPI_Buffer_detach - Removes an existing buffer (for use in MPI_Bsend etc) SYNOPSIS int MPI_Buffer_detach(void *buffer_addr, int *size) int MPI_Buffer_detach_c(void *buffer_addr, MPI_Count *size) OUTPUT PARAMETERS buffer_addr - initial buffer address (choice) size - buffer size, in bytes (integer) NOTES The reason that MPI_Buffer_detach returns the address and size of the buffer being detached is to allow nested libraries to replace and re- store the buffer. For example, consider int size, mysize, idummy; void *ptr, *myptr, *dummy; MPI_Buffer_detach(&ptr, &size); MPI_Buffer_attach(myptr, mysize); . . . . . . library code ... . . . MPI_Buffer_detach(&dummy, &idummy); MPI_Buffer_attach(ptr, size); This is much like the action of the Unix signal routine and has the same strengths (it is simple) and weaknesses (it only works for nested usages). Note that for this approach to work, MPI_Buffer_detach must return MPI_SUCCESS even when there is no buffer to detach. In that case, it returns a size of zero. The MPI 1.1 standard for MPI_BUFFER_DETACH contains the text The statements made in this section describe the behavior of MPI for buffered-mode sends. When no buffer is currently associated, MPI behaves as if a zero-sized buffer is associated with the process. This could be read as applying only to the various Bsend routines. This implementation takes the position that this applies to MPI_BUFFER_DETACH as well. THREAD AND INTERRUPT SAFETY The user is responsible for ensuring that multiple threads do not try to update the same MPI object from different threads. This routine should not be used from within a signal handler. The MPI standard defined a thread-safe interface but this does not mean that all routines may be called without any thread locks. For example, two threads must not attempt to change the contents of the same MPI_Info object concurrently. The user is responsible in this case for using some mechanism, such as thread locks, to ensure that only one thread at a time makes use of this routine. Because the buffer for buffered sends (e.g., MPI_Bsend ) is shared by all threads in a process, the user is responsible for ensuring that only one thread at a time calls this routine or MPI_Buffer_attach . NOTES FOR FORTRAN All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement. All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran. The Fortran binding for this routine is different. Because Fortran does not have pointers, it is impossible to provide a way to use the output of this routine to exchange buffers. In this case, only the size field is set. NOTES FOR C Even though the bufferptr argument is declared as void * , it is really the address of a void pointer. See the rationale in the standard for more details. ERRORS All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for com- municators), MPI_File_set_errhandler (for files), and MPI_Win_set_er- rhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue when- ever possible. MPI_SUCCESS - No error; MPI routine completed successfully. MPI_ERR_ARG - Invalid argument. Some argument is invalid and is not identi- fied by a specific error class (e.g., MPI_ERR_RANK ). MPI_ERR_OTHER - Other error; use MPI_Error_string to get more information about this error code. SEE ALSO MPI_Buffer_attach 2/3/2025 MPI_Buffer_detach(3)
NAME | SYNOPSIS | OUTPUT PARAMETERS | NOTES | THREAD AND INTERRUPT SAFETY | NOTES FOR FORTRAN | NOTES FOR C | ERRORS | SEE ALSO
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