A debug-stream session created after the consumer had already gone away was
leaked permanently. Both consumers awaited StartStreamAsync (up to 30s) and only
then published the session; a circuit teardown / client disconnect inside that
window ran the release path first, found nothing registered and stopped nothing.
The session stayed registered in the singleton DebugStreamService, whose
keepalive renews registered sessions forever (the 5-minute orphan reaper only
collects UNregistered ones), pinning the site gRPC subscription, the
DebugStreamBridgeActor and the dead consumer's object graph until process
restart.
Both call sites now publish the session and re-check liveness under a single
monitor, so exactly one side tears it down and neither can miss it:
- DebugView.Connect/Dispose/Disconnect share a _sessionLock; Dispose sets
_disposed and takes the session in one step, Connect publishes only if not
disposed and otherwise stops the session it just created. Dispose can run off
the renderer's thread, so the Blazor sync context is not relied on. Disconnect
and the onTerminated callback go through the same take-once helper, which also
makes a repeated Dispose stop-once instead of stop-again.
- DebugStreamHub uses the per-connection Items monitor: OnDisconnectedAsync marks
the connection gone before releasing, SubscribeInstance publishes only if
neither that flag nor ConnectionAborted is set, and UnsubscribeInstance takes
the id atomically.
DebugStreamService.StartStreamAsync/StopStream become virtual purely as a test
seam (no behaviour change, keepalive/orphan contract untouched) so the race can
be driven deterministically by a gated stub.
Tests: DebugViewConnectDisposeRaceTests (3) + DebugStreamHubSubscribeRaceTests
(3). Verified fail-unfixed: with the two source fixes stashed, both
dispose-mid-start tests report zero StopStream calls and the DebugView
double-dispose test reports two.
Joseph Doherty
561582747e