private static void EventLeakFixedByWeakEventListener()
{
var source = new EventSource();
var subscriber = new EventSubscriber {
Name = "subscriber"
};
subscriber.SubscribeWithWeakEventListener(source);
Console.WriteLine("Show event subscription in action");
source.GiveSignal("blah!");
Console.WriteLine("Done. Remove subscriber.");
Console.WriteLine("No need to unsubscribe, since weak listener");
Console.WriteLine("allows the subscriber to be collected");
subscriber = null;
GC.Collect();
GC.WaitForPendingFinalizers();
Console.WriteLine("Are we done? Was the subscriber destroyed? What about the listener?");
Console.WriteLine("The weak listener is held onto by the source, however this isn't");
Console.WriteLine("too bad since the listener doesn't take up much space.");
Console.WriteLine("");
Console.WriteLine("Let's kill the source now");
source = null;
GC.Collect();
GC.WaitForPendingFinalizers();
Console.WriteLine("");
Console.WriteLine("The weak listener will also be cleaned up if the event fires after");
Console.WriteLine("the subscriber has been destroyed. This will only happen if you've");
Console.WriteLine("configured the 'OnDetachAction'");
source = new EventSource();
subscriber = new EventSubscriber {
Name = "subscriber"
};
subscriber.SubscribeWithWeakEventListener(source);
Console.WriteLine("Show event subscription in action");
source.GiveSignal("blah!");
Console.WriteLine("Destroy the subscriber, then fire the event again. Is the weak listener finalised?");
subscriber = null;
GC.Collect();
GC.WaitForPendingFinalizers();
source.GiveSignal("blah!");
GC.Collect();
GC.WaitForPendingFinalizers();
Console.WriteLine("");
Console.WriteLine("Note that this is a drawback of this listener - the source event");
Console.WriteLine("must occur to clean up the weak listener. We could call Detach(),");
Console.WriteLine("but that defeats the purpose - why not use regular events if you");
Console.WriteLine("know when to unsubscribe?");
}
private static void EventLeak()
{
var source = new EventSource();
var subscriber = new EventSubscriber {
Name = "leaky subscriber"
};
subscriber.SubscribeWithPlusEquals(source);
Console.WriteLine("Show event subscription in action");
source.GiveSignal("blah!");
Console.WriteLine("Done. Remove subscriber. Naive dev will expect to see finaliser run here.");
subscriber = null;
GC.Collect();
GC.WaitForPendingFinalizers();
Console.WriteLine("Are we done? Was the subscriber destroyed? No!");
Console.WriteLine("The subscriber is held on to by the source until it is destroyed");
Console.WriteLine("Destroying souce now...");
source = null;
GC.Collect();
GC.WaitForPendingFinalizers();
}
private static void EventLeakFixedByWeakEventManager()
{
var source = new EventSource();
var subscriber = new EventSubscriber {
Name = "weak subscriber"
};
subscriber.SubscribeWithWeakEventManager(source);
Console.WriteLine("Show event subscription in action");
source.GiveSignal("blah!");
Console.WriteLine("Done. Remove subscriber.");
Console.WriteLine("No need to unsubscribe, since weak reference to subscriber");
Console.WriteLine("allows the subscriber to be collected");
subscriber = null;
GC.Collect();
GC.WaitForPendingFinalizers();
Console.WriteLine("Are we done? Was the subscriber destroyed?");
}
private static void EventLeakFixedByUnsubscribing()
{
var source = new EventSource();
var subscriber = new EventSubscriber {
Name = "diligent subscriber"
};
subscriber.SubscribeWithPlusEquals(source);
Console.WriteLine("Show event subscription in action");
source.GiveSignal("blah!");
Console.WriteLine("Done. Unsubscribe from source and remove subscriber.");
Console.WriteLine("The missing unsubscribe action was what caused the classic leak");
subscriber.UnsubscribeMinusEquals(source);
subscriber = null;
GC.Collect();
GC.WaitForPendingFinalizers();
Console.WriteLine("Are we done? Was the subscriber destroyed?");
}
