SWI-Prolog -- listen/2

Documentation
- Reference manual
  - The SWI-Prolog library
    - library(broadcast): Broadcast and receive event notifications
- Packages

Availability::- use_module(library(broadcast)).(can be autoloaded)

listen(+Template, :Goal)

Register a listen channel. Whenever a term unifying Template is broadcasted, call Goal. The following example traps all broadcasted messages as a variable unifies to any message. It is commonly used to debug usage of the library.

?- listen(Term, (writeln(Term),fail)).
?- broadcast(hello(world)).
hello(world)
true.

Examples

Using a multicast UDP network

Although the broadcast networks are the default. multicast networks have the advantage that you do not need to know your IP address and, with router support, they can be used on a WAN. Therefore simplest way to initialise the network to make two or more processes communicate on a LAN is using a multicast network:

?- udp_broadcast_initialize(ip(239,0,0,2), [method(multicast)]).
?- listen(write(X), writeln(X)).
?- broadcast(udp(subnet, write(hello))).
hello

See also: - IPv4 Multicast Address Space Registry. The range 239.0.0.0 - 239.255.255.255 is reserved as Organization-Local Scope.