Notify watchers only on output changes and pass previous values to callbacks

StoneRed.LogicSimulator.Simulation/CycleCircuitSimulator.cs

@@ -6,6 +6,7 @@ public sealed class CycleCircuitSimulator : SimulatorBase
 {
     private int[] nextInputMasks = [];
     private Action<int[], int[], int[]> computeOutputs = (_, _, _) => { };
+    private int[] previousOutputMasks = [];
 
     protected override void EnsureStorage()
     {
@@ -13,6 +14,7 @@ public sealed class CycleCircuitSimulator : SimulatorBase
         if (nextInputMasks.Length != gateKinds.Count)
         {
             nextInputMasks = new int[gateKinds.Count];
+            previousOutputMasks = new int[gateKinds.Count];
         }
     }
 
@@ -20,10 +22,9 @@ public sealed class CycleCircuitSimulator : SimulatorBase
     {
         base.Reset();
         Array.Clear(nextInputMasks);
+        Array.Clear(previousOutputMasks);
     }
 
-    protected override void OnSourceChanged(int gateId) { }
-
     public override void Step()
     {
         EnsureCompiled();
@@ -32,9 +33,13 @@ public sealed class CycleCircuitSimulator : SimulatorBase
             Reset();
         }
 
+        (outputMasks, previousOutputMasks) = (previousOutputMasks, outputMasks);
         computeOutputs(inputMasks, outputMasks, sourceStates);
         PropagateAndSwap();
-        NotifyAllWatchers();
+        if (hasAnyWatchers)
+        {
+            NotifyAllWatchers(previousOutputMasks);
+        }
     }
 
     private void PropagateAndSwap()
@@ -103,9 +108,13 @@ public sealed class CycleCircuitSimulator : SimulatorBase
         while (changed && steps < maxSteps)
         {
             steps++;
+            (outputMasks, previousOutputMasks) = (previousOutputMasks, outputMasks);
             computeOutputs(inputMasks, outputMasks, sourceStates);
             changed = PropagateAndSwapDetectChange();
-            NotifyAllWatchers();
+            if (hasAnyWatchers)
+            {
+                NotifyAllWatchers(previousOutputMasks);
+            }
         }
         return !changed;
     }

StoneRed.LogicSimulator.Simulation/SimulatorBase.cs

@@ -28,6 +28,7 @@ public abstract class SimulatorBase : ICircuitSimulator
     private readonly List<GateWatcherEntry> allWatchers = [];
     private Action<int, int>[][] watcherCache = [];
     private int[] gatesWithWatchers = [];
+    protected bool hasAnyWatchers;
     protected int nextWatcherId;
 
     protected sealed record GateWatcherEntry(int Id, int GateId, Action<int, int> Callback);
@@ -169,6 +170,7 @@ public abstract class SimulatorBase : ICircuitSimulator
         GateWatcherEntry entry = new GateWatcherEntry(id, gateId, callback);
         allWatchers.Add(entry);
         RebuildWatcherCache();
+        compiled = false;
         return new GateWatcherSubscription(this, id);
     }
 
@@ -176,6 +178,7 @@ public abstract class SimulatorBase : ICircuitSimulator
     {
         _ = allWatchers.RemoveAll(w => w.Id == id);
         RebuildWatcherCache();
+        compiled = false;
     }
 
     private void RebuildWatcherCache()
@@ -193,18 +196,22 @@ public abstract class SimulatorBase : ICircuitSimulator
         }
 
         gatesWithWatchers = [.. activeGates];
+        hasAnyWatchers = allWatchers.Count > 0;
     }
 
-    protected void NotifyAllWatchers()
+    protected void NotifyAllWatchers(int[] previousOutputMasks)
     {
         for (int i = 0; i < gatesWithWatchers.Length; i++)
         {
             int gateId = gatesWithWatchers[i];
-            Action<int, int>[] callbacks = watcherCache[gateId];
+            if (outputMasks[gateId] != previousOutputMasks[gateId])
-            int val = outputMasks[gateId];
-            for (int j = 0; j < callbacks.Length; j++)
             {
-                callbacks[j](gateId, val);
+                Action<int, int>[] callbacks = watcherCache[gateId];
+                int val = outputMasks[gateId];
+                for (int j = 0; j < callbacks.Length; j++)
+                {
+                    callbacks[j](gateId, val);
+                }
             }
         }
     }
@@ -275,7 +282,7 @@ public abstract class SimulatorBase : ICircuitSimulator
             GateKind.Buffer => Expression.Condition(Expression.NotEqual(Expression.And(inMask, Expression.Constant(1)), Expression.Constant(0)), Expression.Constant(1), Expression.Constant(0)),
             GateKind.Sink => Expression.Condition(Expression.NotEqual(Expression.And(inMask, Expression.Constant(1)), Expression.Constant(0)), Expression.Constant(1), Expression.Constant(0)),
             GateKind.Lut => Expression.ArrayIndex(lutDataConst, Expression.Add(Expression.Constant(lutOffsets[gateId]), Expression.And(inMask, Expression.Constant(lutMasks[gateId])))),
-            _ => throw new ArgumentOutOfRangeException(),
+            _ => throw new InvalidOperationException($"Unknown gate kind: {gateKinds[gateId]}")
         };
     }
 

StoneRed.LogicSimulator.Tests/SimulatorTests.cs

@@ -46,7 +46,6 @@ public abstract class SimulatorTestsBase
             Assert.AreEqual(expected, sim.GetOutput(sink), $"AND2 failed for {i1} & {i2}");
         }
 
-        sim.Reset();
         Check(false, false, false);
         Check(false, true, false);
         Check(true, false, false);
@@ -73,7 +72,6 @@ public abstract class SimulatorTestsBase
             Assert.AreEqual(expected, sim.GetOutput(sink), $"OR2 failed for {i1} | {i2}");
         }
 
-        sim.Reset();
         Check(false, false, false);
         Check(false, true, true);
         Check(true, false, true);
@@ -90,7 +88,6 @@ public abstract class SimulatorTestsBase
         sim.ConnectGates(s1, not, 0);
         sim.ConnectGates(not, sink, 0);
 
-        sim.Reset();
         sim.SetSource(s1, false);
         _ = sim.RunUntilStable();
         Assert.IsTrue(sim.GetOutput(sink), "NOT(0) should be 1");
@@ -118,7 +115,6 @@ public abstract class SimulatorTestsBase
         sim.ConnectGates(s3, lut, 2);
         sim.ConnectGates(lut, sink, 0);
 
-        sim.Reset();
         _ = sim.RunUntilStable();
 
         sim.SetSource(s1, true); sim.SetSource(s2, true); sim.SetSource(s3, false);
@@ -149,9 +145,50 @@ public abstract class SimulatorTestsBase
         sim.ConnectGates(src, inst.Inputs[0], 0);
         sim.ConnectGates(inst.Outputs[0], sink, 0);
 
-        sim.Reset();
         sim.SetSource(src, true);
         _ = sim.RunUntilStable();
         Assert.IsFalse(sim.GetOutput(sink), "Macro NOT(1) should be 0");
     }
+
+    [TestMethod]
+    public void TestWatcherNotification()
+    {
+        ICircuitSimulator sim = CreateSimulator();
+        int source = sim.AddGate(GateKind.Source);
+        int not = sim.AddGate(GateKind.Not);
+        sim.ConnectGates(source, not, 0);
+
+        int watcher1Count = 0;
+        int watcher2Count = 0;
+
+        IDisposable sub1 = sim.WatchGate(not, (id, val) => watcher1Count++);
+        IDisposable sub2 = sim.WatchGate(not, (id, val) => watcher2Count++);
+
+        // Initial state
+        sim.SetSource(source, false);
+        _ = sim.RunUntilStable();
+        Assert.AreEqual(1, watcher1Count, "Watcher 1 should fire on initial change");
+        Assert.AreEqual(1, watcher2Count, "Watcher 2 should fire on initial change");
+
+        // No change
+        sim.SetSource(source, false);
+        _ = sim.RunUntilStable();
+        Assert.AreEqual(1, watcher1Count, "Watcher 1 should not fire if no change");
+        Assert.AreEqual(1, watcher2Count, "Watcher 2 should not fire if no change");
+
+        // Change
+        sim.SetSource(source, true);
+        _ = sim.RunUntilStable();
+        Assert.AreEqual(2, watcher1Count, "Watcher 1 should fire on second change");
+        Assert.AreEqual(2, watcher2Count, "Watcher 2 should fire on second change");
+
+        // Dispose one watcher
+        sub2.Dispose();
+
+        // Change again
+        sim.SetSource(source, false);
+        _ = sim.RunUntilStable();
+        Assert.AreEqual(3, watcher1Count, "Watcher 1 should fire after sub2 is disposed");
+        Assert.AreEqual(2, watcher2Count, "Watcher 2 should NOT fire after being disposed");
+    }
 }