In .NET 6, thread ID in agent log shows generic name instead of numeric thread ID

[nr-ahemsath]

When running the agent attached to a .NET 6 Preview application, the agent's log file shows messages like this:

“NewRelic FINEST: [pid: 24300, tid: .NET ThreadPool Worker]” instead of having the tid field be a numeric thread ID as it currently is in all other .NET runtimes. We're assuming this is because the .NET threadpool is re-implemented in managed code in .NET 6.

More specifically, our Log4Net logging template uses the %thread formatting directive. Under the covers, Log4Net first tries to get the thread's name and then falls back to getting the numeric thread ID if no name is set. Apparently pre-.NET 6 the threadpool threads were not named by default, and in .NET 6 they will be. See this SO discussion for more context and a possible solution: https://stackoverflow.com/questions/42675024/log4net-printing-threadid-and-thread-name-in-the-log/44112461