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_Bsend(3) MPI MPI_Bsend(3) NAME
MPI_Bsend - Basic send with user-provided buffering SYNOPSIS
int MPI_Bsend(void *buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm) INPUT PARAMETERS
buf - initial address of send buffer (choice) count - number of elements in send buffer (nonnegative integer) datatype - datatype of each send buffer element (handle) dest - rank of destination (integer) tag - message tag (integer) comm - communicator (handle) NOTES
This send is provided as a convenience function; it allows the user to send messages without worring about where they are buffered (because the user must have provided buffer space with MPI_Buffer_attach ). In deciding how much buffer space to allocate, remember that the buffer space is not available for reuse by subsequent MPI_Bsend s unless you are certain that the message has been received (not just that it should have been received). For example, this code does not allocate enough buffer space MPI_Buffer_attach( b, n*sizeof(double) + MPI_BSEND_OVERHEAD ); for (i=0; i<m; i++) { MPI_Bsend( buf, n, MPI_DOUBLE, ... ); } because only enough buffer space is provided for a single send, and the loop may start a second MPI_Bsend before the first is done making use of the buffer. In C, you can force the messages to be delivered by MPI_Buffer_detach( &b, &n ); MPI_Buffer_attach( b, n ); (The MPI_Buffer_detach will not complete until all buffered messages are delivered.) THREAD AND INTERRUPT SAFETY
This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe. 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. 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 communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (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 guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible. MPI_SUCCESS - No error; MPI routine completed successfully. MPI_ERR_COMM - Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank ). MPI_ERR_COUNT - Invalid count argument. Count arguments must be non-negative; a count of zero is often valid. MPI_ERR_TYPE - Invalid datatype argument. May be an uncommitted MPI_Datatype (see MPI_Type_commit ). MPI_ERR_RANK - Invalid source or destination rank. Ranks must be between zero and the size of the communicator minus one; ranks in a receive ( MPI_Recv , MPI_Irecv , MPI_Sendrecv , etc.) may also be MPI_ANY_SOURCE . MPI_ERR_TAG - Invalid tag argument. Tags must be non-negative; tags in a receive ( MPI_Recv , MPI_Irecv , MPI_Sendrecv , etc.) may also be MPI_ANY_TAG . The largest tag value is available through the the attribute MPI_TAG_UB . SEE ALSO
MPI_Buffer_attach, MPI_Ibsend, MPI_Bsend_init LOCATION
bsend.c 5/20/2010 MPI_Bsend(3)