Ubuntu Manpage: pvm_mkbuf - Creates a new message buffer.

NAME

       pvm_mkbuf - Creates a new message buffer.

SYNOPSIS

       C    int bufid = pvm_mkbuf( int encoding )

       Fortran   call pvmfmkbuf( encoding, bufid )

PARAMETERS

       encoding
               Integer specifying the buffer's encoding scheme.
               Options in C are:
                    Encoding value           MEANING
                    PvmDataDefault      0    XDR
                    PvmDataRaw          1    no encoding
                    PvmDataInPlace      2    data left in place

               Option names in Fortran are:
                    Encoding value           MEANING
                    PVMDEFAULT          0    XDR
                    PVMRAW              1    no encoding
                    PVMINPLACE          2    data left in place

       bufid   Integer  message  buffer  identifier  returned.  Values less than zero indicate an
               error.

DESCRIPTION

The routine pvm_mkbuf creates a new message buffer and sets its encoding status to
encoding. If pvm_mkbuf is successful, bufid will be the identifier for the new buffer,
which can be used as a send buffer. If some error occurs then bufid will be < 0.

With the default setting XDR encoding is used when packing the message because PVM can not
know if the user is going to add a heterogeneous machine before this message is sent. The
other options to encoding allow the user to take advantage of knowledge about his virtual
machine even when it is heterogeneous. For example, if the user knows that the next
message will only be sent to a machine that understands the native format, then he can use
PvmDataRaw encoding and save on encoding costs.

PvmDataInPlace encoding specifies that data be left in place during packing. The message
buffer only contains the sizes and pointers to the items to be sent. When pvm_send is
called the items are copied directly out of the user's memory. This option decreases the
number of times a message is copied at the expense of requiring the user to not modify the
items between the time they are packed and the time they are sent.

pvm_mkbuf is required if the user wishes to manage multiple message buffers and should be
used in conjunction with pvm_freebuf. pvm_freebuf should be called for a send buffer
after a message has been sent and is no longer needed.

Receive buffers are created automatically by the pvm_recv and pvm_nrecv routines and do
not have to be freed unless they have been explicitly saved with pvm_setrbuf.

Typically multiple send and receive buffers are not needed and the user can simply use the
pvm_initsend routine to reset the default send buffer.

There are several cases where multiple buffers are useful. One example where multiple
message buffers are needed involves libraries or graphical interfaces that use PVM and
interact with a running PVM application but do not want to interfere with the
application's own communication.

When multiple buffers are used they generally are made and freed for each message that is
packed.

RESTRICTIONS

       PvmDataInPlace  allows  only dense (stride = 1) data in version 3.3.  It cannot be used on
       shared memory (*MP) architectures; a PvmNotImpl error will occur at send time.

EXAMPLES

       C:
            bufid = pvm_mkbuf( PvmDataRaw );
            /* send message */
            info = pvm_freebuf( bufid );

       Fortran:
            CALL PVMFMKBUF(PVMDEFAULT, MBUF)
       *    SEND MESSAGE HERE
            CALL PVMFFREEBUF( MBUF, INFO )

ERRORS

       These error conditions can be returned by pvm_mkbuf
            PvmBadParam    giving an invalid encoding value.
            PvmNoMem       Malloc has failed. There is not enough memory
                           to create the buffer