Can we avoid running IdleTrackingBackgroundService if HTTP Server transport is configured as stateless?

[srogovtsev]

From what I can see in the code, IdleTrackingBackgroundService will check for sessions to clear even if server is configured as stateless - which seems somewhat wasteful if we know that there'll never be an open session to clear. This is probably even more relevant after 1.2.0 which pushes to "stateless by default".

csharp-sdk/src/ModelContextProtocol.AspNetCore/IdleTrackingBackgroundService.cs

Lines 38 to 44 in 54caccc

	var timeProvider = _options.Value.TimeProvider;
	using var timer = new PeriodicTimer(TimeSpan.FromSeconds(5), timeProvider);
	while (!stoppingToken.IsCancellationRequested && await timer.WaitForNextTickAsync(stoppingToken))
	{
	await _sessions.PruneIdleSessionsAsync(stoppingToken);
	}

The fix seems to be as simple as overriding StartAsync:

public override Task StartAsync(CancellationToken cancellationToken)
{
  if (_options.Value.Stateless)
    return Task.CompletedTask;

  return base.StartAsync(cancellationToken);
}

PS I've asked this in the discussions space (#1485), but as there was no response, I'm not sure it was a proper place.

[jayaraman-venkatesan]

This is a good catch @srogovtsev . stateless requests never register in _sessions, there is nothing to prune.

I am wondering instead of having a idle background service to support the stateful session cleanup , a per-session CancellationTokenSource would eliminate both problems:

Start a timer when referenceCount drops to 0 — UnreferenceDisposable.DisposeAsync. The session just went idle; start CancelAfter(IdleTimeout).

Cancel the timer when the session is reacquired — AcquireReferenceAsync. A new request arrived; discard the pending cancellation.

This makes expiry event-driven rather than sweep-based: a session is cleaned up exactly at LastActivity + IdleTimeout, not up to 5 seconds later

The one major piece remaining piece will be moving DisposeAllSessionsAsync (currently in IdleTrackingBackgroundService finally) to a shutdown hook on StatefulSessionManager itself, which would allow IdleTrackingBackgroundService to be removed entirely.