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mpi_buffer_detach(3openmpi) [osx man page]

MPI_Buffer_detach(3OpenMPI)											       MPI_Buffer_detach(3OpenMPI)

NAME
MPI_Buffer_detach - Removes an existing buffer (for use in MPI_Bsend, etc.) SYNTAX
C Syntax #include <mpi.h> int MPI_Buffer_detach(void *buf, int *size) Fortran Syntax INCLUDE 'mpif.h' MPI_BUFFER_DETACH(BUF, SIZE, IERROR) <type> BUF(*) INTEGER SIZE, IERROR C++ Syntax #include <mpi.h> int Detach_buffer(void*& buffer) OUTPUT PARAMETERS
buf Initial buffer address (choice). size Buffer size, in bytes (integer). IERROR Fortran only: Error status (integer). DESCRIPTION
Detach the buffer currently associated with MPI. The call returns the address and the size of the detached buffer. This operation will block until all messages currently in the buffer have been transmitted. Upon return of this function, the user may reuse or deallocate the space taken by the buffer. Example: Calls to attach and detach buffers. #define BUFFSIZE 10000 int size char *buff; MPI_Buffer_attach( malloc(BUFFSIZE), BUFFSIZE); /* a buffer of 10000 bytes can now be used by MPI_Bsend */ MPI_Buffer_detach( &buff, &size); /* Buffer size reduced to zero */ MPI_Buffer_attach( buff, size); /* Buffer of 10000 bytes available again */ 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 restore 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's simple) and weaknesses (it only works for nested usages). For 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. For C: Even though the buf argument is declared as void, it is really the address of a void pointer. See Rationale, below, for more details. Even though the C functions MPI_Buffer_attach and MPI_Buffer_detach both have a first argument of type void*, these arguments are used dif- ferently: A pointer to the buffer is passed to MPI_Buffer_attach; the address of the pointer is passed to MPI_Buffer_detach, so that this call can return the pointer value. ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ func- tions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI:Exception object. Before the error value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; 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. SEE ALSO
MPI_Buffer_attach MPI_Bsend Open MPI 1.2 September 2006 MPI_Buffer_detach(3OpenMPI)

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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, int *size) OUTPUT PARAMETERS
buffer - 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 restore 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_BUF- FER_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 buf- fer 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. SEE ALSO
MPI_Buffer_attach LOCATION
buffree.c 5/20/2010 MPI_Buffer_detach(3)
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