ADDMHF (3)
Install message-handler functions.
pvm_delmhf - Remove message-handler functions.
SYNOPSIS
B
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
The tag sent with the message.
The context sent with the message.
Function to call when message received.
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
SEE ALSO
pvm_setrbuf(3PVM) pvm_setsbuf(3PVM) pvm_freebuf(3PVM)
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