fix: prevent duplicated scheduling of callbacks

Author: egil

docs/TimeProviderExtensions.AutoAdvanceBehavior.md

@@ -32,7 +32,7 @@ public System.TimeSpan ClockAdvanceAmount { get; set; }
 #### Exceptions
 
 [System.ArgumentOutOfRangeException](https://docs.microsoft.com/en-us/dotnet/api/System.ArgumentOutOfRangeException 'System.ArgumentOutOfRangeException')  
-Thrown when set to a value than [System.TimeSpan.Zero](https://docs.microsoft.com/en-us/dotnet/api/System.TimeSpan.Zero 'System.TimeSpan.Zero').
+Thrown when set to a value less than [System.TimeSpan.Zero](https://docs.microsoft.com/en-us/dotnet/api/System.TimeSpan.Zero 'System.TimeSpan.Zero').
 
 ### Remarks
 Set to [System.TimeSpan.Zero](https://docs.microsoft.com/en-us/dotnet/api/System.TimeSpan.Zero 'System.TimeSpan.Zero') to disable auto advance. The default value is [System.TimeSpan.Zero](https://docs.microsoft.com/en-us/dotnet/api/System.TimeSpan.Zero 'System.TimeSpan.Zero').
@@ -54,7 +54,7 @@ public System.TimeSpan TimestampAdvanceAmount { get; set; }
 #### Exceptions
 
 [System.ArgumentOutOfRangeException](https://docs.microsoft.com/en-us/dotnet/api/System.ArgumentOutOfRangeException 'System.ArgumentOutOfRangeException')  
-Thrown when set to a value than [System.TimeSpan.Zero](https://docs.microsoft.com/en-us/dotnet/api/System.TimeSpan.Zero 'System.TimeSpan.Zero').
+Thrown when set to a value less than [System.TimeSpan.Zero](https://docs.microsoft.com/en-us/dotnet/api/System.TimeSpan.Zero 'System.TimeSpan.Zero').
 
 ### Remarks
 Set to [System.TimeSpan.Zero](https://docs.microsoft.com/en-us/dotnet/api/System.TimeSpan.Zero 'System.TimeSpan.Zero') to disable auto advance. The default value is [System.TimeSpan.Zero](https://docs.microsoft.com/en-us/dotnet/api/System.TimeSpan.Zero 'System.TimeSpan.Zero').

docs/TimeProviderExtensions.ManualTimeProvider.md

@@ -241,7 +241,7 @@ The [ManualTimeProvider](TimeProviderExtensions.ManualTimeProvider.md 'TimeProvi
 
 ### Remarks
 Override this methods to return a custom implementation of [ManualTimer](TimeProviderExtensions.ManualTimer.md 'TimeProviderExtensions.ManualTimer'). This also allows for intercepting and wrapping
-the provided timer [callback](TimeProviderExtensions.ManualTimeProvider.md#TimeProviderExtensions.ManualTimeProvider.CreateManualTimer(System.Threading.TimerCallback,object,TimeProviderExtensions.ManualTimeProvider).callback 'TimeProviderExtensions.ManualTimeProvider.CreateManualTimer(System.Threading.TimerCallback, object, TimeProviderExtensions.ManualTimeProvider).callback') and [state](TimeProviderExtensions.ManualTimeProvider.md#TimeProviderExtensions.ManualTimeProvider.CreateManualTimer(System.Threading.TimerCallback,object,TimeProviderExtensions.ManualTimeProvider).state 'TimeProviderExtensions.ManualTimeProvider.CreateManualTimer(System.Threading.TimerCallback, object, TimeProviderExtensions.ManualTimeProvider).state'), enabling more advanced testing scenarioes.
+the provided timer [callback](TimeProviderExtensions.ManualTimeProvider.md#TimeProviderExtensions.ManualTimeProvider.CreateManualTimer(System.Threading.TimerCallback,object,TimeProviderExtensions.ManualTimeProvider).callback 'TimeProviderExtensions.ManualTimeProvider.CreateManualTimer(System.Threading.TimerCallback, object, TimeProviderExtensions.ManualTimeProvider).callback') and [state](TimeProviderExtensions.ManualTimeProvider.md#TimeProviderExtensions.ManualTimeProvider.CreateManualTimer(System.Threading.TimerCallback,object,TimeProviderExtensions.ManualTimeProvider).state 'TimeProviderExtensions.ManualTimeProvider.CreateManualTimer(System.Threading.TimerCallback, object, TimeProviderExtensions.ManualTimeProvider).state'), enabling more advanced testing scenarios.
 
 <a name='TimeProviderExtensions.ManualTimeProvider.CreateTimer(System.Threading.TimerCallback,object,System.TimeSpan,System.TimeSpan)'></a>
 

docs/TimeProviderExtensions.ManualTimer.md

@@ -3,7 +3,7 @@
 
 ## ManualTimer Class
 
-A implementaiton of a [System.Threading.ITimer](https://docs.microsoft.com/en-us/dotnet/api/System.Threading.ITimer 'System.Threading.ITimer') whose callbacks are scheduled via a [ManualTimeProvider](TimeProviderExtensions.ManualTimeProvider.md 'TimeProviderExtensions.ManualTimeProvider').
+A implementation of a [System.Threading.ITimer](https://docs.microsoft.com/en-us/dotnet/api/System.Threading.ITimer 'System.Threading.ITimer') whose callbacks are scheduled via a [ManualTimeProvider](TimeProviderExtensions.ManualTimeProvider.md 'TimeProviderExtensions.ManualTimeProvider').
 
 ```csharp
 public class ManualTimer :

src/TimeProviderExtensions/ManualTimeProvider.cs

@@ -1,5 +1,6 @@
 using System.Diagnostics;
 using System.Globalization;
+using System.Runtime.CompilerServices;
 
 namespace TimeProviderExtensions;
 
@@ -327,10 +328,13 @@ public void SetUtcNow(DateTimeOffset value)
             while (utcNow <= value && TryGetNext(value) is ManualTimerScheduler { CallbackTime: not null } scheduler)
             {
                 utcNow = scheduler.CallbackTime.Value;
-                scheduler.TimerElapsed();
+                scheduler.TimerElapsed(scheduleNextCallback: true);
             }
 
-            utcNow = value;
+            if (utcNow < value)
+            {
+                utcNow = value;
+            }
 
             Debug.Assert(callbacks.All(x => x.CallbackTime > utcNow), "Because there should never by any callbacks scheduled in the past at this point.");
         }
@@ -470,9 +474,13 @@ public void Jump(DateTimeOffset value)
                 // in the jump period and invokes the callback that
                 // number of times. Has to happen at least one time.
                 var callbacksPassed = Math.Max(1, Math.Floor((double)jump.Ticks / scheduler.Period.Ticks));
-                for (int i = 0; i < callbacksPassed; i++)
+
+                // Invoke scheduler.TimerElapsed with scheduleNextCallback = false
+                // to prevent duplicates in the callbacks collection.
+                // Only the last call should schedule next callback.
+                for (int invocations = 0; invocations < callbacksPassed; invocations++)
                 {
-                    scheduler.TimerElapsed();
+                    scheduler.TimerElapsed(scheduleNextCallback: invocations == callbacksPassed - 1);
                 }
             }
 
@@ -500,7 +508,7 @@ internal void ScheduleCallback(ManualTimerScheduler scheduler, TimeSpan waitTime
     {
         lock (callbacks)
         {
-            Debug.Assert(!callbacks.Contains(scheduler), "A scheduler should only be added to callbacks one time.");
+            Debug.Assert(!callbacks.Contains(scheduler), "A scheduler should only be added to callbacks one time, and is expected to be removed before callback is invoked.");
 
             scheduler.CallbackTime = utcNow + waitTime;
 
@@ -517,11 +525,11 @@ internal void ScheduleCallback(ManualTimerScheduler scheduler, TimeSpan waitTime
         }
     }
 
-    internal void RemoveCallback(ManualTimerScheduler timerCallback)
+    internal void RemoveCallback(ManualTimerScheduler scheduler)
     {
         lock (callbacks)
         {
-            var existingIndexOf = callbacks.FindIndex(0, x => ReferenceEquals(x, timerCallback));
+            var existingIndexOf = callbacks.FindIndex(0, x => ReferenceEquals(x, scheduler));
             if (existingIndexOf >= 0)
             {
                 callbacks.RemoveAt(existingIndexOf);

src/TimeProviderExtensions/ManualTimerScheduler.cs

@@ -51,13 +51,13 @@ internal void Change(TimeSpan dueTime, TimeSpan period)
         }
     }
 
-    internal void TimerElapsed()
+    internal void TimerElapsed(bool scheduleNextCallback)
     {
         CallbackTime = null;
         callback.Invoke(state);
         CallbackInvokeCount++;
 
-        if (Period != Timeout.InfiniteTimeSpan && Period != TimeSpan.Zero)
+        if (scheduleNextCallback && Period != Timeout.InfiniteTimeSpan && Period != TimeSpan.Zero)
         {
             ScheduleCallback(Period);
         }
@@ -67,7 +67,7 @@ private void ScheduleCallback(TimeSpan waitTime)
     {
         if (waitTime == TimeSpan.Zero)
         {
-            TimerElapsed();
+            TimerElapsed(scheduleNextCallback: true);
         }
         else
         {

test/TimeProviderExtensions.Tests/ManualTimeProviderTests.cs

@@ -318,7 +318,6 @@ public void ActiveTimers_with_after_timer_state_change()
         sut.ActiveTimers.Should().Be(0);
     }
 
-
     [Fact]
     public void CreateManualTimer_with_custom_timer_type()
     {

test/TimeProviderExtensions.Tests/ManualTimeProviderTimerTests.cs

@@ -209,4 +209,30 @@ public void Jumping_past_longer_than_recurrence()
 
         callbackTimes.Should().Equal(startTime + target);
     }
+
+    [Fact]
+    public void jumping_causes_multiple_timers_invokes_callback_in_order()
+    {
+        var sut = new ManualTimeProvider();
+        var callbacks = new List<(int timerId, TimeSpan callbackTime)>();
+        var startTime = sut.GetTimestamp();
+        using var timer1 = sut.CreateTimer(_ => callbacks.Add((1, sut.GetElapsedTime(startTime))), null, TimeSpan.FromMilliseconds(3), TimeSpan.FromMilliseconds(3));
+        using var timer2 = sut.CreateTimer(_ => callbacks.Add((2, sut.GetElapsedTime(startTime))), null, TimeSpan.FromMilliseconds(3), TimeSpan.FromMilliseconds(3));
+        using var timer3 = sut.CreateTimer(_ => callbacks.Add((3, sut.GetElapsedTime(startTime))), null, TimeSpan.FromMilliseconds(6), TimeSpan.FromMilliseconds(5));
+
+        sut.Jump(TimeSpan.FromMilliseconds(3));
+        sut.Jump(TimeSpan.FromMilliseconds(3));
+        sut.Jump(TimeSpan.FromMilliseconds(3));
+        sut.Jump(TimeSpan.FromMilliseconds(2));
+
+        callbacks.Should().Equal(
+            (1, TimeSpan.FromMilliseconds(3)),
+            (2, TimeSpan.FromMilliseconds(3)),
+            (3, TimeSpan.FromMilliseconds(6)),
+            (1, TimeSpan.FromMilliseconds(6)),
+            (2, TimeSpan.FromMilliseconds(6)),
+            (1, TimeSpan.FromMilliseconds(9)),
+            (2, TimeSpan.FromMilliseconds(9)),
+            (3, TimeSpan.FromMilliseconds(11)));
+    }
 }