fix: accessing null object (cache) after shutdown

[egil]

This fixes a NullReferenceException, that I think happens in GetQueueMessagesAsync when it tries to acces this.cache after EventHubAdapterReceiver.Shutdown() has been called.

This only happens under high load.

Here is the stack trace I have seen in production multiple times.

System.NullReferenceException:
   at Orleans.Streaming.EventHubs.EventHubAdapterReceiver+<GetQueueMessagesAsync>d__22.MoveNext (Orleans.Streaming.EventHubs, Version=9.0.0.0, Culture=neutral, PublicKeyToken=null: /_/src/Azure/Orleans.Streaming.EventHubs/Providers/Streams/EventHub/EventHubAdapterReceiver.cs:181)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Orleans.Streams.PersistentStreamPullingAgent+<ReadFromQueue>d__34.MoveNext (Orleans.Streaming, Version=9.0.0.0, Culture=neutral, PublicKeyToken=null: /_/src/Orleans.Streaming/PersistentStreams/PersistentStreamPullingAgent.cs:434)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Orleans.Internal.AsyncExecutorWithRetries+<ExecuteWithRetriesHelper>d__4`1.MoveNext (Orleans.Core, Version=9.0.0.0, Culture=neutral, PublicKeyToken=null: /_/src/Orleans.Core/Async/AsyncExecutorWithRetries.cs:241)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Orleans.Internal.AsyncExecutorWithRetries+<ExecuteWithRetriesHelper>d__4`1.MoveNext (Orleans.Core, Version=9.0.0.0, Culture=neutral, PublicKeyToken=null: /_/src/Orleans.Core/Async/AsyncExecutorWithRetries.cs:272)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Orleans.Streams.PersistentStreamPullingAgent+<PumpQueue>d__33.MoveNext (Orleans.Streaming, Version=9.0.0.0, Culture=neutral, PublicKeyToken=null: /_/src/Orleans.Streaming/PersistentStreams/PersistentStreamPullingAgent.cs:363)

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull Request Overview

This PR fixes a NullReferenceException that occurs when accessing the cache field after EventHubAdapterReceiver.Shutdown() has been called, particularly under high load conditions.

• Adds null-conditional operator when accessing this.cache in GetQueueMessagesAsync
• Uses null-coalescing operator to handle potential null messageStreamPositions
• Includes minor formatting improvements with additional newlines

Comments suppressed due to low confidence (1)

src/Azure/Orleans.Streaming.EventHubs/Providers/Streams/EventHub/EventHubAdapterReceiver.cs:1

• The GetCacheCursor method still accesses this.cache directly without null checking, which could cause the same NullReferenceException after shutdown. Consider adding null safety here as well.

using System;

[shacal]

Cleaner, I like it :)