/* Part of SWI-Prolog Author: Jan Wielemaker E-mail: J.Wielemaker@vu.nl WWW: http://www.swi-prolog.org Copyright (c) 2006-2013, University of Amsterdam VU University Amsterdam All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ :- module(broadcast, [ listen/3, % Listener x Templ x Goal listen/2, % Templ x Goal unlisten/1, % Listener unlisten/2, % Listener x Templ unlisten/3, % Listener x Templ x Goal listening/3, % Listener x Templ x Goal broadcast/1, % Templ broadcast_request/1 % Templ ]). :- meta_predicate listen(+, 0), listen(+, +, 0), unlisten(+, +, 0). :- dynamic listener/4. /** Event service Generic broadcasting service. Broadcasts are made using the predicate broadcast(+Templ). All registered `listeners' will have their goal called. Success or failure of this is ignored. The listener can not bind arguments. This library is particulary useful for disconnecting modules in an application. Modules can broadcast events such as changes, anticipating other modules need to react on such changes. For example, settings.pl broadcasts changes to settings, allowing dependent modules to react on changes: == :- listing(setting(changed(http:workers, New)), change_workers(New)). change_workers(New) :- setting(http:port, Port), http_workers(Port, New). == */ %! listen(+Listener, +Templ, :Goal) is det. %! listen(+Templ, :Goal) is det. % % Open a channel for listening for events of the given `Templ'. listen(Listener0, Templ, Module:Goal) :- canonical_listener(Listener0, Listener), assert_listener(Templ, Listener, Module, Goal). listen(Templ, Module:Goal) :- assert_listener(Templ, Module, Module, Goal). %! unlisten(+Listener) is det. %! unlisten(+Listener, +Templ) is det. %! unlisten(+Listener, +Templ, :Goal) is det. % % Destroy a channel. All arguments may be variables, removing the % all matching listening channals. unlisten(Listener0) :- canonical_listener(Listener0, Listener), retractall(listener(_, Listener, _, _)). unlisten(Listener0, Templ) :- canonical_listener(Listener0, Listener), retractall(listener(Templ, Listener, _, _)). unlisten(Listener0, Templ, Module:Goal) :- canonical_listener(Listener0, Listener), retract_listener(Templ, Listener, Module, Goal). %! listening(?Listener, ?Templ, ?Goal) is nondet. % % returns currently open channels listening(Listener0, Templ, Module:Goal) :- canonical_listener(Listener0, Listener), listener(Templ, Listener, Module, Goal). %! broadcast(+Templ) is det. % % Broadcast given event. broadcast(Templ) :- ( listener(Templ, _Listener, Module, Goal), ( Module:Goal -> fail ) ; true ). %! broadcast_request(+Templ) is nondet. % % Broadcast given event till accepted. Succeeds then, fail if no % listener accepts the call. Bindings made by the listener goal % are maintained. May be used to make broadcast requests. broadcast_request(Templ) :- listener(Templ, _Listener, Module, Goal), Module:Goal. % {assert,retract}_listener(+Templ, +Listener, +Module, +Goal) % % Implemented as sub-predicate to ensure storage in this module. % Second registration is ignored. Is this ok? It avoids problems % using multiple registration of global listen channels. assert_listener(Templ, Listener, Module, TheGoal) :- listener(Templ, Listener, Module, TheGoal), !. assert_listener(Templ, Listener, Module, TheGoal) :- asserta(listener(Templ, Listener, Module, TheGoal)). retract_listener(Templ, Listener, Module, TheGoal) :- retractall(listener(Templ, Listener, Module, TheGoal)). %! canonical_listener(+Raw, -Canonical) % % Entry for later optimization. canonical_listener(Templ, Templ).