bionic (3) pvm_addmhf.3PVM.gz

NAME

       pvm_addmhf, pvm_delmhf - Install or remove message-handler functions.

SYNOPSIS

       C    int mhid = pvm_addmhf( int src, int tag, int ctx, int (*func)(int mid) )
            int info = pvm_delmhf( int mhid )

       Fortran   Not available

PARAMETERS

       src    The tid of the sender.

       tag    The tag sent with the message.

       ctx    The context sent with the message.

       func   Function to call when message received.

       mhid   Message handler id.

       info   Result code.

       mid    Message buffer identifier for new active receive buffer.

DESCRIPTION

       pvm_addmhf  specifies  a  function  that  will be called whenever libpvm copies in a message whose header
       fields of src, tag, and ctx match those provided to pvm_addmhf().

       The src and tag fields may be left unspecified (wildcard) by setting to -1.

       The calling sequence of the message handler function is:

            int handler( int mid )

       Where mid is the bufid of the received message.  The handler function can be used to unpack  and  process
       the  received  message  buffer.   PVM  automatically  saves  the current send and receive buffers, so the
       handler need not worry about interfering with message buffers in the regular program flow.  PVM also sets
       the  current  receive  buffer  to  the received message (using pvm_setrbuf()) before invoking the message
       handler, so the message can be unpacked directly.  PVM will free this message  buffer  when  the  message
       handler  returns,  if the handler has not already done so.  But, any other message buffers created by the
       handler routine should be freed using pvm_freebuf() before returning.

       Note: Operation in the message handler context is somewhat restricted.  The function may  call  some  PVM
       functions, but not others.  For example, it may compose and send a reply message as shown:

            pvm_packf( "%+ %s", PvmDataDefault, "got your message" );
            pvm_send( tid, tag );
            pvm_freebuf( pvm_setsbuf( 0 ) );

       or equivalently:

            pvm_setsbuf( pvm_mkbuf( PvmDataDefault ) );
            pvm_pkstr( "got your message" );
            pvm_send( tid, tag );
            pvm_freebuf( pvm_setsbuf( 0 ) );

       but is not allowed to call certain other PVM communication functions, such as multicast or receive.

       pvm_addmhf  returns  the id number of the newly created message handler if successful; this number may be
       passed to pvm_delmhf to remove the entry.  There is no guarantee to the ordering of id values returned by
       pvm_addmhf,  or  to  the  order  in which message handlers will be invoked.  PvmExists is returned if the
       handler already exists.

       pvm_delmhf returns PvmOk if successful.  PvmBadParam  if  pvm_delmhf  is  passed  a  negative  id  value.
       PvmNotFound if the id value is not found.

EXAMPLES

            /* Print a message when hosts are added to virtual machine */

            int
            hostAdded( int mid )
            {
                 int n;
                 pvm_unpackf( "%d", &n );
                 printf( "*** %d new hosts just added ***\n", n );
            }

            void
            main()
            {
                 int src, tag, ctx;

                 . . .

                 src = -1;
                 tag = 99;
                 ctx = -1;

                 pvm_addmhf( src, tag, ctx, hostAdded );
                 pvm_notify( PvmHostAdd, 99, -1, (int *) NULL );

                 . . .
            }

ERRORS

       The following error conditions can be returned by pvm_addmhf():

       PvmExists
              Can't insert as handler already exists with same (tag, ctx, src) including "wild-cards" (those set
              to -1)

       The following error conditions can be returned by pvm_delmhf():

       PvmBadParam
              Invalid (negative) mhid passed in.

       PvmNotFound
              Message handler mhid does not exist.

SEE ALSO

       pvm_setrbuf(3PVM), pvm_setsbuf(3PVM), pvm_freebuf(3PVM)

                                                  1 April, 1997                                     ADDMHF(3PVM)