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MKBUF(3PVM)			PVM Version 3.4			   MKBUF(3PVM)

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	encod-
       ing  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 al-
       low 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 di-
       rectly 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_free-
       buf  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 buf-
       fer.

       There are several cases where multiple buffers are useful.  One example
       where multiple message buffers are needed involves libraries or graphi-
       cal 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

SEE ALSO
       pvm_initsend(3PVM), pvm_freebuf(3PVM)

				30 August, 1993			   MKBUF(3PVM)

NAME | SYNOPSIS | PARAMETERS | DESCRIPTION | RESTRICTIONS | EXAMPLES | ERRORS | SEE ALSO

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