.TH MPI_Buffer_attach 3 "11/12/2019" " " "MPI"

.SH NAME

MPI_Buffer_attach \-  Attaches a user-provided buffer for sending 

.SH SYNOPSIS

.nf

int MPI_Buffer_attach(void *buffer, int size)

.fi

.SH INPUT PARAMETERS

.PD 0

.TP

.B buffer 

- initial buffer address (choice)

.PD 1

.PD 0

.TP

.B size 

- buffer size, in bytes (integer)

.PD 1

.SH NOTES

The size given should be the sum of the sizes of all outstanding Bsends that

you intend to have, plus 

.I MPI_BSEND_OVERHEAD

for each Bsend that you do.

For the purposes of calculating size, you should use 

.I MPI_Pack_size

\&.

In other words, in the code

.nf

MPI_Buffer_attach(buffer, size);

MPI_Bsend(..., count=20, datatype=type1,  ...);

\&.

\&.

\&.

MPI_Bsend(..., count=40, datatype=type2, ...);

.fi

the value of 

.I size

in the 

.I MPI_Buffer_attach

call should be greater than

the value computed by

.nf

MPI_Pack_size(20, type1, comm, &s1;;

MPI_Pack_size(40, type2, comm, &s2;;

size = s1 + s2 + 2 * MPI_BSEND_OVERHEAD;

.fi

The 

.I MPI_BSEND_OVERHEAD

gives the maximum amount of space that may be used in

the buffer for use by the BSEND routines in using the buffer.  This value

is in 

.I mpi.h

(for C) and 

.I mpif.h

(for Fortran).

.SH 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 

.I 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., 

.I 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 

.I MPI_Buffer_detach

\&.

.SH NOTES FOR FORTRAN

All MPI routines in Fortran (except for 

.I MPI_WTIME

and 

.I MPI_WTICK

) have

an additional argument 

.I ierr

at the end of the argument list.  

.I 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

.I call

statement.

All MPI objects (e.g., 

.I MPI_Datatype

, 

.I MPI_Comm

) are of type 

.I INTEGER

in Fortran.

.SH ERRORS

All MPI routines (except 

.I MPI_Wtime

and 

.I 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 

.I MPI_Comm_set_errhandler

(for communicators),

.I MPI_File_set_errhandler

(for files), and 

.I MPI_Win_set_errhandler

(for

RMA windows).  The MPI-1 routine 

.I MPI_Errhandler_set

may be used but

its use is deprecated.  The predefined error handler

.I MPI_ERRORS_RETURN

may be used to cause error values to be returned.

Note that MPI does 

.B not

guarentee that an MPI program can continue past

an error; however, MPI implementations will attempt to continue whenever

possible.

.PD 0

.TP

.B MPI_SUCCESS 

- No error; MPI routine completed successfully.

.PD 1

.PD 0

.TP

.B MPI_ERR_BUFFER 

- Invalid buffer pointer.  Usually a null buffer where

one is not valid.

.PD 1

.PD 0

.TP

.B MPI_ERR_INTERN 

- An internal error has been detected.  This is fatal.

Please send a bug report to 

.I mpi-bugs@mcs.anl.gov

\&.

.PD 1

.SH SEE ALSO

MPI_Buffer_detach, MPI_Bsend

.br