Performance upgrade for Debounce/Throttle

src/Library/DeclarativeProperty/DebounceProperty.cs

@@ -1,52 +1,68 @@
 namespace DeclarativeProperty;
 
-public sealed class DebounceProperty<T> : TimingPropertyBase<T>
+public sealed class DebounceProperty<T> : DeclarativePropertyBase<T>
 {
-    private CancellationTokenSource? _debounceCts;
+    private readonly object _lock = new();
-    private bool _isActive;
+    private readonly Func<TimeSpan> _interval;
-    private DateTime _startTime;
+    private DateTime _startTime = DateTime.MinValue;
+    private T? _nextValue;
+    private CancellationToken _nextCancellationToken;
+    private bool _isThrottleTaskRunning;
     public bool ResetTimer { get; init; }
-    public TimeSpan WaitInterval { get; init; } = TimeSpan.FromMilliseconds(1);
+    public TimeSpan WaitInterval { get; init; } = TimeSpan.FromMilliseconds(10);
 
     public DebounceProperty(
         IDeclarativeProperty<T> from,
         Func<TimeSpan> interval,
-        Action<T?>? setValueHook = null) : base(from, interval, setValueHook)
+        Action<T?>? setValueHook = null) : base(from.Value, setValueHook)
     {
+        _interval = interval;
+        AddDisposable(from.Subscribe(SetValue));
     }
 
-    protected override Task SetValue(T? next, CancellationToken cancellationToken = default)
+    private Task SetValue(T? next, CancellationToken cancellationToken = default)
     {
-        _debounceCts?.Cancel();
+        lock (_lock)
-        var newTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
-        _debounceCts = newTokenSource;
-
-        var newToken = newTokenSource.Token;
-        
-        if (!_isActive || ResetTimer)
         {
-            _isActive = true;
+            _nextValue = next;
-            _startTime = DateTime.Now;
+            _nextCancellationToken = cancellationToken;
-        }
+            
-
+            if (_isThrottleTaskRunning)
-        Task.Run(async () =>
-        {
-            try
             {
-                while (DateTime.Now - _startTime < Interval())
+                if (ResetTimer)
                 {
-                    await Task.Delay(WaitInterval, newToken);
+                    _startTime = DateTime.Now;
                 }
-
+                return Task.CompletedTask;
-                WithLock(() => { _isActive = false; });
-
-                await FireAsync(next, cancellationToken);
             }
-            catch (TaskCanceledException ex)
+
-            {
+            _startTime = DateTime.Now;
-            }
+            _isThrottleTaskRunning = true;
-        });
+            Task.Run(async () => await StartDebounceTask());
+        }
 
         return Task.CompletedTask;
     }
+
+    private async Task StartDebounceTask()
+    {
+        while (DateTime.Now - _startTime < _interval())
+        {
+            await Task.Delay(WaitInterval);
+        }
+
+        T? next;
+        CancellationToken cancellationToken;
+        lock (_lock)
+        {
+            _isThrottleTaskRunning = false;
+            next = _nextValue;
+            cancellationToken = _nextCancellationToken;
+        }
+
+        await SetNewValueAsync(
+            next,
+            cancellationToken
+        );
+    }
 }

src/Library/DeclarativeProperty/DeclarativeProperty.cs

@@ -18,9 +18,24 @@ public sealed class DeclarativeProperty<T> : DeclarativePropertyBase<T>
 
     public DeclarativeProperty(T initialValue, Action<T?>? setValueHook = null) : base(initialValue, setValueHook)
     {
-
     }
 
     public async Task SetValue(T newValue, CancellationToken cancellationToken = default)
         => await SetNewValueAsync(newValue, cancellationToken);
+
+    public void SetValueSafe(T newValue, CancellationToken cancellationToken = default)
+    {
+        SetNewValueSync(newValue, cancellationToken);
+        if (cancellationToken.IsCancellationRequested) return;
+        Task.Run(async () =>
+        {
+            try
+            {
+                await NotifySubscribersAsync(newValue, cancellationToken);
+            }
+            catch
+            {
+            }
+        });
+    }
 }

src/Library/DeclarativeProperty/DeclarativePropertyBase.cs

@@ -52,7 +52,7 @@ public abstract class DeclarativePropertyBase<T> : IDeclarativeProperty<T>
     {
         _subscribers.Add(onChange);
         onChange(_value, default);
-        
+
         return new Unsubscriber<T>(this, onChange);
     }
 
@@ -84,6 +84,13 @@ public abstract class DeclarativePropertyBase<T> : IDeclarativeProperty<T>
         });
 
     protected async Task SetNewValueAsync(T? newValue, CancellationToken cancellationToken = default)
+    {
+        SetNewValueSync(newValue, cancellationToken);
+        if (cancellationToken.IsCancellationRequested) return;
+        await NotifySubscribersAsync(newValue, cancellationToken);
+    }
+
+    protected void SetNewValueSync(T? newValue, CancellationToken cancellationToken = default)
     {
         if (!(Value?.Equals(newValue) ?? false))
         {
@@ -102,8 +109,6 @@ public abstract class DeclarativePropertyBase<T> : IDeclarativeProperty<T>
                     }
 
                     _triggerDisposables.Clear();
-                    
-                    if(cancellationToken.IsCancellationRequested) return;
                 }
 
                 _value = newValue;
@@ -112,18 +117,16 @@ public abstract class DeclarativePropertyBase<T> : IDeclarativeProperty<T>
                 {
                     foreach (var subscribeTrigger in _subscribeTriggers)
                     {
-                        if(cancellationToken.IsCancellationRequested) return;
-                        
                         var disposable = subscribeTrigger(this, _value);
                         if (disposable != null) _triggerDisposables.Add(disposable);
                     }
                 }
             }
 
+            if (cancellationToken.IsCancellationRequested) return;
+
             OnPropertyChanged(nameof(Value));
         }
-
-        await NotifySubscribersAsync(newValue, cancellationToken);
     }
 
     public async Task ReFireAsync()

src/Library/DeclarativeProperty/DeclarativePropertyExtensions.cs

@@ -12,6 +12,12 @@ public static class DeclarativePropertyExtensions
     public static IDeclarativeProperty<T> Debounce<T>(this IDeclarativeProperty<T> from, Func<TimeSpan> interval, bool resetTimer = false)
         => new DebounceProperty<T>(from, interval) {ResetTimer = resetTimer};
 
+    public static IDeclarativeProperty<T> Throttle<T>(this IDeclarativeProperty<T> from, TimeSpan interval)
+        => new ThrottleProperty<T>(from, () => interval);
+
+    public static IDeclarativeProperty<T> Throttle<T>(this IDeclarativeProperty<T> from, Func<TimeSpan> interval)
+        => new ThrottleProperty<T>(from, interval);
+
     public static IDeclarativeProperty<T> DistinctUntilChanged<T>(this IDeclarativeProperty<T> from)
         => new DistinctUntilChangedProperty<T>(from);
 

src/Library/DeclarativeProperty/ThrottleProperty.cs

@@ -1,59 +1,35 @@
 namespace DeclarativeProperty;
 
-public class ThrottleProperty<T> : TimingPropertyBase<T>
+public class ThrottleProperty<T> : DeclarativePropertyBase<T>
 {
-    private CancellationTokenSource? _debounceCts;
+    private readonly object _lock = new();
-    private DateTime _lastFired;
+    private DateTime _lastFired = DateTime.MinValue;
+    private readonly Func<TimeSpan> _interval;
 
     public ThrottleProperty(
         IDeclarativeProperty<T> from,
         Func<TimeSpan> interval,
-        Action<T?>? setValueHook = null) : base(from, interval, setValueHook)
+        Action<T?>? setValueHook = null) : base(from.Value, setValueHook)
     {
+        _interval = interval;
+        AddDisposable(from.Subscribe(SetValue));
     }
 
-    protected override Task SetValue(T? next, CancellationToken cancellationToken = default)
+    private async Task SetValue(T? next, CancellationToken cancellationToken = default)
     {
-        _debounceCts?.Cancel();
+        lock (_lock)
-        var interval = Interval();
-        if (DateTime.Now - _lastFired > interval)
         {
-            _lastFired = DateTime.Now;
+            if (DateTime.Now - _lastFired < _interval())
-            // Note: Recursive chains can happen. Awaiting this can cause a deadlock.
-            Task.Run(async () => await FireAsync(next, cancellationToken));
-        }
-        else
-        {
-            _debounceCts = new();
-            Task.Run(async () =>
             {
-                try
+                return;
-                {
+            }
-                    await Task.Delay(interval, _debounceCts.Token);
-                    await FireIfNeededAsync(
-                        next,
-                        () => { _lastFired = DateTime.Now; },
-                        _debounceCts.Token, cancellationToken
-                    );
-                    /*var shouldFire = WithLock(() =>
-                    {
-                        if (_debounceCts.Token.IsCancellationRequested)
-                            return false;
 
-                        _lastFired = DateTime.Now;
+            _lastFired = DateTime.Now;
-                        return true;
-                    });
-
-                    if (!shouldFire) return;
-
-                    await Fire(next, cancellationToken);*/
-                }
-                catch (TaskCanceledException ex)
-                {
-                }
-            });
         }
-        
+
-        return Task.CompletedTask;
+        await SetNewValueAsync(
+            next,
+            cancellationToken
+        );
     }
 }

src/Library/DeclarativeProperty/TimingPropertyBase.cs

@@ -1,85 +0,0 @@
-namespace DeclarativeProperty;
-
-public abstract class TimingPropertyBase<T> : DeclarativePropertyBase<T>
-{
-    private readonly SemaphoreSlim _semaphore = new(1, 1);
-    protected Func<TimeSpan> Interval { get; }
-
-    protected TimingPropertyBase(
-        IDeclarativeProperty<T> from,
-        Func<TimeSpan> interval,
-        Action<T?>? setValueHook = null) : base(from.Value, setValueHook)
-    {
-        Interval = interval;
-        AddDisposable(from.Subscribe(SetValueInternal));
-    }
-
-    private async Task SetValueInternal(T? next, CancellationToken cancellationToken = default)
-        => await WithLockAsync(async () => await SetValue(next, cancellationToken), cancellationToken);
-
-
-    protected void WithLock(Action action)
-    {
-        try
-        {
-            _semaphore.Wait();
-            action();
-        }
-        finally
-        {
-            _semaphore.Release();
-        }
-    }
-
-    protected TResult WithLock<TResult>(Func<TResult> func)
-    {
-        try
-        {
-            _semaphore.Wait();
-            return func();
-        }
-        finally
-        {
-            _semaphore.Release();
-        }
-    }
-
-    protected async Task WithLockAsync(Func<Task> action, CancellationToken cancellationToken = default)
-    {
-        try
-        {
-            await _semaphore.WaitAsync(cancellationToken);
-            await action();
-        }
-        finally
-        {
-            _semaphore.Release();
-        }
-    }
-
-    protected abstract Task SetValue(T? next, CancellationToken cancellationToken = default);
-
-    protected async Task FireIfNeededAsync(
-        T? next,
-        Action cleanup,
-        CancellationToken timingCancellationToken = default,
-        CancellationToken cancellationToken = default)
-    {
-        await Task.Delay(Interval(), timingCancellationToken);
-        var shouldFire = WithLock(() =>
-        {
-            if (timingCancellationToken.IsCancellationRequested)
-                return false;
-
-            cleanup();
-            return true;
-        });
-
-        if (!shouldFire) return;
-
-        await FireAsync(next, cancellationToken);
-    }
-
-    protected async Task FireAsync(T? next, CancellationToken cancellationToken = default) 
-        => await SetNewValueAsync(next, cancellationToken);
-}