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[blazor] fix multiple calls to OnConnectionDownAsync #62518

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Merged
merged 5 commits into from
Jul 18, 2025
Merged

[blazor] fix multiple calls to OnConnectionDownAsync #62518

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ebf208f
fix multiple calls to OnConnectionDownAsync
pavelsavara Jul 1, 2025
c25fdf7
Merge branch 'main' into blazor_dedup_OnConnectionDownAsync
pavelsavara Jul 14, 2025
89b709a
fix other scenarios where OnConnectionDownAsync needs to me more expl…
pavelsavara Jul 14, 2025
273fcf1
Merge branch 'main' into blazor_dedup_OnConnectionDownAsync
pavelsavara Jul 16, 2025
4f774f6
feedback
pavelsavara Jul 17, 2025
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15 changes: 14 additions & 1 deletion src/Components/Server/src/Circuits/CircuitHost.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -188,6 +188,16 @@ public Task InitializeAsync(ProtectedPrerenderComponentApplicationStore store, A
}));
}

public bool SetDisconnected()
{
if (Client.Connected)
{
Client.SetDisconnected();
return true;
}
return false;
}

// We handle errors in DisposeAsync because there's no real value in letting it propagate.
// We run user code here (CircuitHandlers) and it's reasonable to expect some might throw, however,
// there isn't anything better to do than log when one of these exceptions happens - because the
Expand All @@ -209,7 +219,10 @@ await Renderer.Dispatcher.InvokeAsync(async () =>

try
{
await OnConnectionDownAsync(CancellationToken.None);
if (this.Client.Connected)
{
await OnConnectionDownAsync(CancellationToken.None);
}
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I don't think this is the right change to fix the metric issue. It's changing an existing behavior of the system that users might be relying on.

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this event is called twice. That's a bug not a feature

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What is causing the 2nd call?

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The proper event is Hub.OnDisconnect()

CircuitHost.OnConnectionDownAsync() is called from CircuitHost.DisposeAsync() regardless if it's connected or not, creating dis-balance.

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@javiercn does this make sense or you have another proposal for the fix ?

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I just tested the "close tab" and "navigate to non-interactive page". Both behave as expected, that is, they call the event once.

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Terminate it's not being fired in those cases.

  • Close tab will likely don't cause unload to fire.
  • navigate to non-interactive page
    • It takes a bit of time for the client to start the circuit disposal.
    • If for some reason it's not happening, it's also a bug.

https://github.com/dotnet/aspnetcore/blob/main/src/Components/Server/src/CircuitDisconnectMiddleware.cs#L81-L87

https://github.com/dotnet/aspnetcore/blob/main/src/Components/Server/src/Circuits/CircuitRegistry.cs#L391

If we check for the circuit to be connected it won't fire when we want to eagerly terminate the circuit.

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Maybe we need to call that event from places that call circuitHost.Client.SetDisconnected() rather than relying that circuitHost.DisposeAsync() would always call it.

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Also I'm not sure that the new PauseAndDisposeCircuitHost is calling SetDisconnected()

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I made the calls to OnConnectionDownAsync more explicit now, instead of relying on the DisposeAsync.

@javiercn please review again.

}
catch
{
Expand Down
5 changes: 0 additions & 5 deletions src/Components/Server/src/Circuits/CircuitMetrics.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -70,11 +70,6 @@ public void OnCircuitDown(long startTimestamp, long currentTimestamp)
_circuitActiveCounter.Add(-1);
}

if (_circuitConnectedCounter.Enabled)
{
_circuitConnectedCounter.Add(-1);
}

if (_circuitDuration.Enabled)
{
var duration = Stopwatch.GetElapsedTime(startTimestamp, currentTimestamp);
Expand Down
25 changes: 18 additions & 7 deletions src/Components/Server/src/Circuits/CircuitRegistry.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -135,12 +135,12 @@ protected virtual bool DisconnectCore(CircuitHost circuitHost, string connection
var result = ConnectedCircuits.TryRemove(circuitId, out circuitHost);
Debug.Assert(result, "This operation operates inside of a lock. We expect the previously inspected value to be still here.");

circuitHost.Client.SetDisconnected();
var previouslyConnected = circuitHost.SetDisconnected();
RegisterDisconnectedCircuit(circuitHost);

Log.CircuitMarkedDisconnected(_logger, circuitId);

return true;
return previouslyConnected;
}

public void RegisterDisconnectedCircuit(CircuitHost circuitHost)
Expand Down Expand Up @@ -309,6 +309,11 @@ private Task PauseAndDisposeCircuitEntry(DisconnectedCircuitEntry entry)

private async Task PauseAndDisposeCircuitHost(CircuitHost circuitHost, bool saveStateToClient)
{
if (circuitHost.SetDisconnected())
{
await circuitHost.Renderer.Dispatcher.InvokeAsync(() => circuitHost.OnConnectionDownAsync(default));
}

await _circuitPersistenceManager.PauseCircuitAsync(circuitHost, saveStateToClient);
circuitHost.UnhandledException -= CircuitHost_UnhandledException;
await circuitHost.DisposeAsync();
Expand Down Expand Up @@ -376,10 +381,12 @@ private void DisposeTokenSource(DisconnectedCircuitEntry entry)
}

// We don't expect this to throw. User code only runs inside DisposeAsync and that does its own error handling.
public ValueTask TerminateAsync(CircuitId circuitId)
public async ValueTask TerminateAsync(CircuitId circuitId)
{
CircuitHost circuitHost;
DisconnectedCircuitEntry entry = default;
var circuitHandlerTask = Task.CompletedTask;

lock (CircuitRegistryLock)
{
if (ConnectedCircuits.TryGetValue(circuitId, out circuitHost) || DisconnectedCircuits.TryGetValue(circuitId.Secret, out entry))
Expand All @@ -388,17 +395,21 @@ public ValueTask TerminateAsync(CircuitId circuitId)
DisconnectedCircuits.Remove(circuitId.Secret);
ConnectedCircuits.TryRemove(circuitId, out _);
Log.CircuitDisconnectedPermanently(_logger, circuitHost.CircuitId);
circuitHost.Client.SetDisconnected();

if (circuitHost.SetDisconnected())
{
circuitHandlerTask = circuitHost.Renderer.Dispatcher.InvokeAsync(() => circuitHost.OnConnectionDownAsync(default));
}
}
}

await circuitHandlerTask;

if (circuitHost != null)
{
circuitHost.UnhandledException -= CircuitHost_UnhandledException;
return circuitHost.DisposeAsync();
await circuitHost.DisposeAsync();
}

return default;
}

// We don't need to do anything with the exception here, logging and sending exceptions to the client
Expand Down
9 changes: 4 additions & 5 deletions src/Components/Server/test/Circuits/CircuitMetricsTest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -108,15 +108,11 @@ public async Task OnCircuitDown_UpdatesCountersAndRecordsDuration()

// Assert
var activeMeasurements = activeCircuitCounter.GetMeasurementSnapshot();
var connectedMeasurements = connectedCircuitCounter.GetMeasurementSnapshot();
var durationMeasurements = circuitDurationCollector.GetMeasurementSnapshot();

Assert.Single(activeMeasurements);
Assert.Equal(-1, activeMeasurements[0].Value);

Assert.Single(connectedMeasurements);
Assert.Equal(-1, connectedMeasurements[0].Value);

Assert.Single(durationMeasurements);
Assert.True(durationMeasurements[0].Value > 0);
}
Expand Down Expand Up @@ -162,7 +158,10 @@ public void FullCircuitLifecycle_RecordsAllMetricsCorrectly()
// 4. Connection re-established
circuitMetrics.OnConnectionUp();

// 5. Circuit closes
// 5. Connection drops
circuitMetrics.OnConnectionDown();

// 6. Circuit closes
Thread.Sleep(10); // Add a small delay to ensure a measurable duration
var endTime = Stopwatch.GetTimestamp();
circuitMetrics.OnCircuitDown(startTime, endTime);
Expand Down
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