How does asynclocal work for HttpRequestLatencyListener

[ShawnTMS]

From my understanding, the EventListener callback such as OnEventWritten should be triggered in the same process as the http request but does not guarantee it runs in the same async context. Why does AsyncLocal work in this library that during event callbacks, it can do the checkpoints and logs the latency of the event based on the initial request sent timestamp in HttpLatencyTelemetryHandler? Upon checking the bottom of the code, I did not find where and how this is done in other places either.

[ShawnTMS]

This post only mentioned the code runs in the same process https://learn.microsoft.com/en-us/dotnet/fundamentals/networking/telemetry/events#eventlistener, but somehow it also share the same AsyncContext after testing locally.

Can someone share more details about how it works internally, I could not find any official documents that talk about it.