JVM does not exit immediately after main method exits when akka-actor instrumentation is enabled

[NomadBlacky]

Describe the bug

When using OpenTelemetry Java agent v2.9.0 or later with Akka, it takes a long time from the end of the main method to the end of the JVM.

Steps to reproduce

• https://github.com/NomadBlacky/scala-cli-playland/tree/1bc3ee2c3e9ae3c8fcd0376f7fd49f7de7b0ea2a/opentelemetry-akka-issue

Expected behavior

The JVM exits immediately after the main method finishes.

Actual behavior

The JVM does not exit immediately after the main method exits.

Javaagent or library instrumentation version

javaagent v2.9.0 or later

Environment

JDK: temurin:21
OS:

ProductName:            macOS
ProductVersion:         14.6.1
BuildVersion:           23G93

Additional context

No response

[NomadBlacky]

I took a thread dump and found that a non-daemon thread, system-akka.actor.internal-dispatcher-N remained.

• https://github.com/NomadBlacky/scala-cli-playland/blob/1bc3ee2c3e9ae3c8fcd0376f7fd49f7de7b0ea2a/opentelemetry-akka-issue/threaddump.txt

This is supposed to terminate when ActorSystem#terminate is called, but for some reason it continues to exist.
In v2.9.0 an implementation of context propagation was added for the Akka Scheduler (#12373), but I wasn't sure if this was the cause.
I haven't tried it yet, but Pekko may have similar issues.