Added Grab/Release

1 files changed, 29 insertions, 5 deletions

diff --git a/dnn/Trigger.cc b/dnn/Trigger.cc
index 59a3b33..9b6db60 100644
--- a/dnn/Trigger.cc
+++ b/dnn/Trigger.cc
@@ -28,7 +28,8 @@ the trigger.
 Create a trigger with an empty list of associated reaction.
 ?*/
 DnnTrigger :: DnnTrigger ()
-: Subscribers ()
+: Subscribers (),
+  Grabs ()
 {
 }
 
@@ -52,6 +53,24 @@ void
 DnnTrigger :: Unsubscribe (DnnBaseReaction& a)
 {
 	Subscribers.Remove (&a);
+	Grabs.Remove (&a);
+}
+
+/*?nextdoc?*/
+void
+DnnTrigger :: Grab (DnnBaseReaction& a)
+{
+	Grabs.Prepend (&a);
+}
+
+/*?
+Add (resp. Remove) a reaction onto (resp. from) the stack of reactions that preempt
+events caused by this trigger.
+?*/
+void
+DnnTrigger :: Release (DnnBaseReaction& a)
+{
+	Subscribers.Remove (&a);
 }
 
 /*?
@@ -60,8 +79,13 @@ Have a trigger dispatch the event \var{ev} to its associated reactions.
 void
 DnnTrigger :: Dispatch (DnnEvent& ev)
 {
-	CcuListOf <DnnBaseReaction> subscribers = Subscribers;
-	CcuListIterOf <DnnBaseReaction> ai (subscribers);
-	while (++ai)
-		(*ai)->Manage (ev);
+	DnnBaseReaction* r = Grabs.First ();
+	if (r) {
+		r->Manage (ev);
+	} else {
+		CcuListOf <DnnBaseReaction> subscribers = Subscribers;
+		CcuListIterOf <DnnBaseReaction> ai = subscribers;
+		while (++ai)
+			(*ai)->Manage (ev);
+	}
 }