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Fix System.Timers.Timer Stop() not working after setting AutoReset or Interval on disabled one-shot timer #122843

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Merged
stephentoub merged 6 commits into from
Jan 11, 2026
Merged

Fix System.Timers.Timer Stop() not working after setting AutoReset or Interval on disabled one-shot timer #122843

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569303d
Initial plan
Copilot Jan 3, 2026
8518a8f
Fix Timer not stopping after setting AutoReset or Interval on disable…
Copilot Jan 3, 2026
72cb668
Fix potential race condition in StopWorksAfterSettingAutoResetOrInter…
Copilot Jan 4, 2026
0579fc7
Simplify timer test to be deterministic without Thread.Sleep race con…
Copilot Jan 4, 2026
419c4d9
Move _enabled check into UpdateTimer() method
Copilot Jan 8, 2026
cad9f74
Add wait with timeout to verify timer callback doesn't fire after set…
Copilot Jan 9, 2026
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16 changes: 7 additions & 9 deletions src/libraries/System.ComponentModel.TypeConverter/src/System/Timers/Timer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -89,10 +89,7 @@ public bool AutoReset
else if (_autoReset != value)
{
_autoReset = value;
if (_timer != null)
{
UpdateTimer();
}
UpdateTimer();
}
}
}
Expand Down Expand Up @@ -152,7 +149,11 @@ public bool Enabled

private void UpdateTimer()
{
Debug.Assert(_timer != null, $"{nameof(_timer)} was expected not to be null");
if (_timer is null || !_enabled)
{
return;
}

int i = (int)Math.Ceiling(_interval);
_timer.Change(i, _autoReset ? i : Timeout.Infinite);
}
Expand All @@ -172,10 +173,7 @@ public double Interval
}

_interval = value;
if (_timer != null)
{
UpdateTimer();
}
UpdateTimer();
}
}

Expand Down
29 changes: 29 additions & 0 deletions src/libraries/System.ComponentModel.TypeConverter/tests/TimerTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -62,6 +62,7 @@ public void TestTimerStartAutoReset()
target = 10;
mres.Reset();
timer.AutoReset = true;
timer.Start();
mres.Wait();

timer.Stop();
Expand Down Expand Up @@ -114,5 +115,33 @@ public void TestInterval(double interval)
Assert.Equal(interval, timer.Interval);
}
}

[ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
public void SettingAutoResetOrIntervalOnDisabledOneShotTimerDoesNotRestartIt()
{
using (var timer = new TestTimer(1))
{
var mres = new ManualResetEventSlim();

timer.AutoReset = false;
timer.Elapsed += (sender, e) => mres.Set();
timer.Start();

mres.Wait();
Assert.False(timer.Enabled);

// Setting AutoReset should not restart a disabled timer
mres.Reset();
timer.AutoReset = true;
Assert.False(timer.Enabled);
Assert.False(mres.Wait(100), "Timer callback should not have fired after setting AutoReset");

// Setting Interval should not restart a disabled timer
mres.Reset();
timer.Interval = 1;
Assert.False(timer.Enabled);
Assert.False(mres.Wait(100), "Timer callback should not have fired after setting Interval");
}
}
}
}
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