DaemonServerLifecycleTests.DaemonKilled_EveryThinClientExitsNonZero fails intermittently

[RikkiGibson]

@dibarbet for visibility

Failure

The test Microsoft.CodeAnalysis.LanguageServer.ProcessHost.UnitTests.DaemonServerLifecycleTests.DaemonKilled_EveryThinClientExitsNonZero fails intermittently in the Test_Windows_CoreClr_Debug leg of roslyn-CI.

When a daemon server is killed, one of the "thin client" processes exits with code 0 instead of a non-zero exit code, tripping the assertion:

Assert.NotEqual() Failure: Expected: Not 0, Actual: 0

This is a process-lifecycle timing race — under some scheduling, a thin client observes a clean shutdown/exit-0 before the killed-daemon condition propagates, rather than the expected non-zero exit.

Observed

• Build 1528743 (PR Do not report hidden pattern diagnostics #84576) — failed on both the initial run and a /azp run roslyn-CI retry.
  • Windows CoreClr Debug, Helix job bd7fb5e0-3583-41a8-80c7-72a5b0eced81, workitem_9.
• PR Do not report hidden pattern diagnostics #84576 only touches src/Compilers/CSharp + a benchmark file (no LanguageServer changes), so the failure is unrelated to the PR under test.

Error message

{
  "ErrorMessage": "DaemonServerLifecycleTests.DaemonKilled_EveryThinClientExitsNonZero",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1528743
Error message validated: [DaemonServerLifecycleTests.DaemonKilled_EveryThinClientExitsNonZero]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 7/28/2026 5:42:55 PM UTC

Report

Build	Repository	Test	Pull Request
1529969	dotnet/roslyn	workitem_9.WorkItemExecution	#84659
1530290	dotnet/roslyn	workitem_9.WorkItemExecution
1530261	dotnet/roslyn	workitem_9.WorkItemExecution	#84666
1530167	dotnet/roslyn	workitem_9.WorkItemExecution
1530149	dotnet/roslyn	workitem_9.WorkItemExecution
1530139	dotnet/roslyn	workitem_6.WorkItemExecution	#83593
1530113	dotnet/roslyn	workitem_6.WorkItemExecution	#84647
1530093	dotnet/roslyn	workitem_9.WorkItemExecution	#84660
1530086	dotnet/roslyn	workitem_9.WorkItemExecution
1529284	dotnet/roslyn	workitem_6.WorkItemExecution	#84655
1528743	dotnet/roslyn	workitem_9.WorkItemExecution	#84576

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
11	11	11