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@@ -35,8 +35,10 @@
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-module(gproc_ps).
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-export([subscribe/2,
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+ subscribe_cond/3,
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unsubscribe/2,
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publish/3,
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+ publish_cond/3,
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list_subs/2
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]).
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@@ -70,6 +72,37 @@
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subscribe(Scope, Event) when Scope==l; Scope==g ->
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gproc:reg({p,Scope,{?ETag, Event}}).
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+-spec subscribe_cond(scope(), event(), undefined | ets:match_spec()) -> true.
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+%% @doc Subscribe conditionally to events of type `Event'
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+%%
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+%% This function is similar to {@link subscribe/2}, but adds a condition
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+%% in the form of a match specification.
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+%%
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+%% The condition is tested by the {@link publish_cond/3} function
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+%% and a message is delivered only if the condition is true. Specifically,
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+%% the test is:
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+%%
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+%% `ets:match_spec_run([Msg], ets:match_spec_compile(Cond)) == [true]'
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+%%
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+%% In other words, if the match_spec returns true for a message, that message
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+%% is sent to the subscriber. For any other result from the match_spec, the
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+%% message is not sent. `Cond == undefined' means that all messages will be
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+%% delivered (that is, `publish_cond/3' will treat 'normal' subscribers just
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+%% like {@link publish/3} does, except that `publish/3' strictly speaking
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+%% ignores the Value part of the property completely, whereas `publish_cond/3'
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+%% expects it to be either undefined or a valid match spec).
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+%%
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+%% This means that `Cond=undefined' and ``Cond=[{'_',[],[true]}]'' are
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+%% equivalent.
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+%% @end
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+subscribe_cond(Scope, Event, Spec) when Scope==l; Scope==g ->
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+ case Spec of
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+ undefined -> ok;
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+ [_|_] -> _ = ets:match_spec_compile(Spec); % validation
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+ _ -> error(badarg)
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+ end,
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+ gproc:reg({p,Scope,{?ETag, Event}}, Spec).
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+
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-spec unsubscribe(scope(), event()) -> true.
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%% @doc Remove subscribtion created using `subscribe(Scope, Event)'
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%%
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@@ -91,6 +124,31 @@ unsubscribe(Scope, Event) when Scope==l; Scope==g ->
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publish(Scope, Event, Msg) when Scope==l; Scope==g ->
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gproc:send({p, Scope, {?ETag, Event}}, {?ETag, Event, Msg}).
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+-spec publish_cond(scope(), event(), msg()) -> msg().
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+%% @doc Publishes the message `Msg' to conditional subscribers of `Event'
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+%%
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+%% The message will be delivered to each subscriber provided their respective
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+%% condition tests succeed.
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+%%
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+%% @see subscribe_cond/3.
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+%%
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+publish_cond(Scope, Event, Msg) when Scope==l; Scope==g ->
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+ Message = {?ETag, Event, Msg},
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+ lists:foreach(
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+ fun({Pid, undefined}) -> Pid ! Message;
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+ ({Pid, Spec}) ->
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+ try C = ets:match_spec_compile(Spec),
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+ case ets:match_spec_run([Msg], C) of
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+ [true] -> Pid ! Message;
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+ _ -> ok
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+ end
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+ catch
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+ error:_ ->
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+ ok
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+ end
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+ end, gproc:select({Scope,p}, [{ {{p,Scope,{?ETag,Event}}, '$1', '$2'},
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+ [], [{{'$1','$2'}}] }])).
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+
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-spec list_subs(scope(), event()) -> [pid()].
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%% @doc List the pids of all processes subscribing to `Event'
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Ulf Wiger