Description

There is a deadlock that occurs transiently when our .NET 6.0 application is starting. From the call stack, the application is hanging on a call to Threadpool.GetMaxThreads(). Looking at the dump with repro with the 2 deadlocked threads, the deadlock involves locking around the ThreadPool type constructor and a lock taken in the EventListener class:

The dump has been shared with the .NET team, filing this issue at the request of the .NET team for tracking.

Reproduction Steps

It's a not trivial repro. It involves running a .NET 6.0 app that calls into Threadpool.GetMaxThreads() during application startup and an external entity (on the same machine) triggering an ETW session that, in turn instantiates EventSource inside the application at the same time.

From David Mason (@davmason):

Expected behavior

No deadlock.

Actual behavior

There is a deadlock.

Regression?

No response

Known Workarounds

@davmason suggested creating the EventListener explicitly before calling ThreadPool.GetMaxThreads() as a workaround. I can confirm this works.

class RuntimeEventListener : EventListener
{
    internal static int eventCount;

    protected override void OnEventSourceCreated(EventSource eventSource)
    {
        base.OnEventSourceCreated(eventSource);

        if (eventSource.Name.Equals("System.Runtime"))
        {
            Dictionary<string, string> refreshInterval = new Dictionary<string, string>();
            refreshInterval["EventCounterIntervalSec"] = "1";
            EnableEvents(source, EventLevel.Informational, (EventKeywords)(-1), refreshInterval);
        }
    }

    protected override void OnEventWritten(EventWrittenEventArgs eventData)
    {
        base.OnEventWritten(eventData);
    }
}

And then create one at the beginning of Main before calling ThreadPool.GetMaxThreads():
RuntimeEventListener listener = new RuntimeEventListener();

Configuration

.NET 6.0.20

Other information

No response