fix: disposing or cancelling cancellation token after timer callback should not throw

Author: egil

src/TimeScheduler/System/Testing/TestPeriodicTimer.cs

@@ -34,7 +34,7 @@ public override ValueTask<bool> WaitForNextTickAsync(CancellationToken cancellat
         cancellationRegistration?.Unregister();
         cancellationRegistration = cancellationToken.Register(() =>
         {
-            completionSource.TrySetCanceled(cancellationToken);
+            completionSource?.TrySetCanceled(cancellationToken);
         });
 
         return new ValueTask<bool>(completionSource.Task);

src/TimeScheduler/Testing/TestScheduler.Timer.cs

@@ -72,6 +72,7 @@ public void Dispose()
             {
                 return;
             }
+
             isDisposed = true;
             callback = null;
             stopTimerCts.Dispose();
@@ -98,6 +99,11 @@ private void TimerElapsed()
 
         private void ScheduleCallback(TimeSpan waitTime)
         {
+            if (isDisposed)
+            {
+                return;
+            }
+
             running = true;
             owner.RegisterFutureAction(
                 owner.GetUtcNow() + waitTime,

src/TimeScheduler/TimeScheduler.csproj

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <Title>Scheduler</Title>
-    <Version>0.7.1</Version>
+    <Version>0.7.2</Version>
     <Company>Egil Hansen</Company>
     <Authors>Egil Hansen</Authors>
     <Description>

test/TimeScheduler.Tests/System/Testing/ManualTimeProviderPeriodicTimerTests.cs

@@ -149,6 +149,29 @@ public void GetUtcNow_matches_time_when_WaitForNextTickAsync_is_invoked()
             startTime + interval * 3);
     }
 
+    [Fact]
+    public async void Cancelling_token_after_WaitForNextTickAsync_safe()
+    {
+        var sut = new ManualTimeProvider();
+        var interval = TimeSpan.FromSeconds(3);
+        using var cts = new CancellationTokenSource();
+        var periodicTimer = sut.CreatePeriodicTimer(interval);
+        var cleanCancelTask = CancelAfterWaitForNextTick(periodicTimer, cts);
+
+        sut.ForwardTime(interval);
+
+        await cleanCancelTask;
+
+        static async Task CancelAfterWaitForNextTick(TimeScheduler.PeriodicTimer periodicTimer, CancellationTokenSource cts)
+        {
+            while (await periodicTimer.WaitForNextTickAsync(cts.Token))
+            {
+                break;
+            }
+            cts.Cancel();
+        }
+    }
+
     static async Task WaitForNextTickInLoop(TimeProvider scheduler, Action callback, TimeSpan interval)
     {
         using var periodicTimer = scheduler.CreatePeriodicTimer(interval);

test/TimeScheduler.Tests/System/Testing/ManualTimeProviderTimerTests.cs

@@ -130,4 +130,15 @@ public void GetUtcNow_matches_time_at_callback_time()
             startTime + interval + interval,
             startTime + interval + interval + interval);
     }
+
+    [Fact]
+    public void Disposing_timer_in_callback()
+    {
+        var interval = TimeSpan.FromSeconds(3);
+        var sut = new ManualTimeProvider();
+        ITimer timer = default!;
+        timer = sut.CreateTimer(_ => timer!.Dispose(), null, interval, interval);
+
+        sut.ForwardTime(interval);
+    }
 }

test/TimeScheduler.Tests/Testing/TestSchedulerPeriodicTimerTests.cs

@@ -137,6 +137,29 @@ public void GetUtcNow_matches_time_when_WaitForNextTickAsync_is_invoked()
             startTime + interval * 3);
     }
 
+    [Fact]
+    public async void Cancelling_token_after_WaitForNextTickAsync_safe()
+    {
+        var sut = new TestScheduler();
+        var interval = TimeSpan.FromSeconds(3);
+        using var cts = new CancellationTokenSource();
+        var periodicTimer = sut.CreatePeriodicTimer(interval);
+        var cleanCancelTask = CancelAfterWaitForNextTick(periodicTimer, cts);
+
+        sut.ForwardTime(interval);
+
+        await cleanCancelTask;
+
+        static async Task CancelAfterWaitForNextTick(TimeScheduler.PeriodicTimer periodicTimer, CancellationTokenSource cts)
+        {
+            while (await periodicTimer.WaitForNextTickAsync(cts.Token))
+            {
+                break;
+            }
+            cts.Cancel();
+        }
+    }
+
     static async Task WaitForNextTickInLoop(TimeProvider scheduler, Action callback, TimeSpan interval)
     {
         using var periodicTimer = scheduler.CreatePeriodicTimer(interval);

test/TimeScheduler.Tests/Testing/TestSchedulerTimerTests.cs

@@ -130,4 +130,15 @@ public void GetUtcNow_matches_time_at_callback_time()
             startTime + interval + interval,
             startTime + interval + interval + interval);
     }
+
+    [Fact]
+    public void Disposing_timer_in_callback()
+    {
+        var interval = TimeSpan.FromSeconds(3);
+        var sut = new TestScheduler();
+        ITimer timer = default!;
+        timer = sut.CreateTimer(_ => timer!.Dispose(), null, interval, interval);
+
+        sut.ForwardTime(interval);
+    }
 }