EventSource dynamic events (Write<T>) will be dispatched to all listeners regardless whether the listener enabled the source

[karolz-ms]

Run the following program to reproduce the problem:

    class Program
    {
        static void Main(string[] args)
        {
        
            var aSource = new AlphaSource();
            var bSource = new BravoSource();
            using (var al = new AlphaListener())
            {
                aSource.AlphaMessage("A1");
                bSource.BravoMessage("B1");

                using (var bl = new BravoListener())
                {
                    aSource.AlphaMessage("A2");
                    bSource.BravoMessage("B2");
                    aSource.Write("Dynamic", new { Message = "A3 dynamic" });

                    Console.ReadKey();
                }
            }         
        }
   }


    [EventSource(Name ="Alpha")]
    class AlphaSource: EventSource
    {
        [Event(1)]
        public void AlphaMessage(string arg)
        {
            this.WriteEvent(1, arg);
        }
    }

    [EventSource(Name = "Bravo")]
    class BravoSource : EventSource
    {
        [Event(1)]
        public void BravoMessage(string arg)
        {
            this.WriteEvent(1, arg);
        }
    }

    class AlphaListener : EventListener
    {
        protected override void OnEventWritten(EventWrittenEventArgs eventData)
        {
            Console.WriteLine($"AlphaListener: got event from {eventData.EventSource.Name}: {eventData.Payload[0]}");
        }

        protected override void OnEventSourceCreated(EventSource source)
        {
            if (source is AlphaSource)
            {
                this.EnableEvents(source, EventLevel.LogAlways, (EventKeywords) (-1));
            }
        }
    }

    class BravoListener : EventListener
    {
        protected override void OnEventWritten(EventWrittenEventArgs eventData)
        {
            Console.WriteLine($"BravoListener: got event from {eventData.EventSource.Name}: {eventData.Payload[0]}");
        }

        protected override void OnEventSourceCreated(EventSource source)
        {
            if (source is BravoSource)
            {
                this.EnableEvents(source, EventLevel.LogAlways, (EventKeywords)(-1));
            }
        }
    }

Talked to @vancem , he thinks it is a legitimate issue in DispatchToAllListeners implementation, specifically the eventId == -1 in the code if (eventId == -1 || dispatcher.m_EventEnabled[eventId])

[karolz-ms]

@brianrob FYI

[vancem]

Two things

First, this is a bug, but it is more like incomplete feature. When Write was added to EventSource, the subscription logic in DispatchToAllListerns was not appropriately completed.

The problem was that Dispatchers (which decide which EvenListeners get event), have a array of Booleans indexed by event ID that make this determination. Write events don't have eventIDs (just names, keywords and levels) and the logic simply ignored this (and unconditionally sent the event to all listeners).

At the very least we should have a bit in the Dispatcher that indicates that the listener has subscribe to the EventSource AT ALL, and skip listeners that did not subscribe at all (that is pretty easy).

However better is that we should dispatch only those Write events that, based on keywords and level, were subscribed by the listener. One way of doing this is to give Write events an event ID (allocated on the fly), and use the existing Boolean array (thus everything happens dynamically). The other way is to remember the keywords and level in the dispatcher and then do the comparison logic in the DispatchToAllListeners.

It will probably take a couple hours to design and code up.

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