Prevent Test Hangs Caused By Concurrent Trace Listener Mutation

[Brian Robbins (brianrob)]

Summary

Prevent assertion dialogs from blocking test runs while preserving parallel execution.

• Stop the ELF mismatch tests from clearing and restoring the process-wide Trace.Listeners collection.
• Eagerly initialize the .NET Framework trace-listener configuration from a TraceEventTests module initializer before xUnit starts test methods in parallel.
• Validate the existing listener configuration before intentionally triggering assertions; the tests do not install or repair listeners.
• Disable interactive assertion UI in test app.config files while retaining ThrowingTraceListener.
• Add the previously missing listener configuration to FastSerialization.Tests.

Root cause

Trace.Listeners is process-wide state and its configuration is loaded lazily. The ELF mismatch tests previously cleared and restored that collection while other tests could use it, allowing assertion tests to run with DefaultTraceListener and open an interactive assertion dialog.

Removing the explicit listener mutation fixed that race, but the full parallel TraceEventTests workload also reproduced concurrent first access to the lazily initialized listener configuration. The module initializer now forces that configuration to finish loading on one thread before any test method executes. Test parallelization remains enabled.

On .NET Framework, AssertValid() verifies that DefaultTraceListener is absent and ThrowingTraceListener was registered by the test assembly's app.config. It only inspects the collection because repairing process-wide listener state could introduce another race. Modern .NET ignores this app.config diagnostics section, but its built-in assertion behavior already throws; the assertion tests verify that behavior directly.

Validation

• TraceEvent.Tests builds successfully for net462 and net8.0.
• Three exact seven-assembly VSTest 18.9.0 Debug/Release stress iterations passed with TraceEvent.Tests parallelization enabled.
• Removing the listener configuration causes the validation test to fail through xUnit within seconds instead of opening an assertion dialog.
• Twenty consecutive public Azure DevOps PR merge-ref runs against 2acb78c01d6d3331e6b091740827b80c15dfd1e9 completed both the PerfView_Debug and PerfView_Release test tasks without a hang. Nineteen builds passed; build 1583681 completed normally but had two unrelated transient TdhEnumerateProviders test failures.

CI build IDs: 1583568, 1583609, 1583612, 1583613, 1583614, 1583615, 1583652, 1583653, 1583654, 1583655, 1583656, 1583678, 1583679, 1583680, 1583681, 1583682, 1583734, 1583735, 1583736, 1583737.