Fix: Host shutdown blocked by extended session idle timeout

[andystaples]

Problem
When extended sessions are enabled, every host stop is delayed by exactly ExtendedSessionIdleTimeoutInSeconds (default 30s). This affects deployments, scale-down events, and restarts.

Root Cause
Two bugs in the shutdown path:

Bug 1 — No cancellation token on session wait: OrchestrationSession.FetchNewOrchestrationMessagesAsync calls messagesAvailableEvent.WaitAsync(this.idleTimeout) without a cancellation token. During shutdown, shutdownSource is cancelled, but this cancellation never reaches active sessions — each session blocks for the full idle timeout before it can be drained. The AsyncAutoResetEvent already supports a CancellationToken overload; it just wasn't being used.

Bug 2 — isForced parameter ignored: AzureStorageOrchestrationService.StopAsync(bool isForced) completely ignores the isForced parameter. Whether forced or graceful, shutdown always waits for sessions to drain naturally.

Fix
Bug 1: Pass the shutdownSource.Token through OrchestrationSessionManager into each OrchestrationSession, and use the two-argument WaitAsync(timeout, cancellationToken) overload in FetchNewOrchestrationMessagesAsync. When the shutdown token is cancelled, the wait exits immediately (returning null), which causes the DTFx dispatcher to close the session.

Bug 2: Add OrchestrationSessionManager.AbortAllSessions() which clears all active sessions, unblocking DrainAsync immediately. AzureStorageOrchestrationService.StopAsync now calls this method when isForced is true, before awaiting appLeaseManager.StopAsync().

[Copilot]

Pull request overview

Fixes Azure Storage backend shutdown delays when extended sessions are enabled by ensuring session waits are cancellable and by honoring forced shutdown semantics to avoid waiting for sessions to drain.

Changes:

• Propagates a shutdown CancellationToken into OrchestrationSession and uses it to cancel idle waits in FetchNewOrchestrationMessagesAsync.
• Adds OrchestrationSessionManager.AbortAllSessions() and calls it from AzureStorageOrchestrationService.StopAsync(isForced: true) to unblock draining during forced shutdown.
• Adds new tests intended to validate cancellation behavior and forced shutdown session abort behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/DurableTask.AzureStorage/OrchestrationSessionManager.cs	Stores shutdown token for sessions; adds AbortAllSessions() to unblock draining during forced shutdown.
src/DurableTask.AzureStorage/Messaging/OrchestrationSession.cs	Cancels extended-session idle waits immediately on shutdown token cancellation.
src/DurableTask.AzureStorage/AzureStorageOrchestrationService.cs	Honors isForced by aborting sessions before stopping lease manager.
Test/DurableTask.AzureStorage.Tests/OrchestrationSessionTests.cs	Adds tests for cancellation/forced shutdown behavior (but currently not wired into the repo’s test project).

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

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[Copilot]

AbortAllSessions() clears only activeOrchestrationSessions, but leaves pendingOrchestrationMessageBatches and the ready-for-processing AsyncQueue buffers intact. Because OrchestrationSessionManager is reused across StartAsync/StopAsync, a forced stop could leave stale in-memory batches that may get processed after a subsequent StartAsync (or just retain memory). Consider also clearing the pending/ready buffers (or recreating the OrchestrationSessionManager on restart) when aborting sessions.

Suggested change

	{
	this.activeOrchestrationSessions.Clear();
	{
	// Clear any active sessions as well as all pending in-memory message batches
	// so that no stale work is processed after a subsequent StartAsync.
	this.activeOrchestrationSessions.Clear();
	this.pendingOrchestrationMessageBatches.Clear();

[Copilot]

This test uses reflection to reach into the private activeOrchestrationSessions field and assumes both the exact field name and concrete type. That makes the test brittle (a simple rename/type change becomes a runtime NullReferenceException/InvalidCastException). Consider asserting sessionsField != null before GetValue, and prefer exercising the manager via exposed/internal APIs (or an internal test hook) to avoid hard-coding private implementation details.

Suggested change

	varsessions=(Dictionary<string,OrchestrationSession>)sessionsField.GetValue(manager);
	Assert.IsNotNull(
	sessionsField,
	"Expected OrchestrationSessionManager to have a non-public instance field named 'activeOrchestrationSessions'.");
	varsessions=sessionsField.GetValue(manager)asIDictionary<string,OrchestrationSession>;
	Assert.IsNotNull(
	sessions,
	"Expected 'activeOrchestrationSessions' field to be assignable to IDictionary<string, OrchestrationSession>.");