Each HttpClient instance creates an additional platform thread for its SelectorManager. With recent updates to NIO/VirtualThreads that thread could now become a VirtualThread. This would avoid having each HttpClient instance use up one platform thread. This is similar to what was done for the HttpClient QuicSelectorThread in [JDK-8369920](https://bugs.openjdk.org/browse/JDK-8369920). This should be transparent for users of the API. An undocumented internal system property is introduced that can revert the change in case of unforeseen trouble.
------------- Commit messages: - 8372159: HttpClient SelectorManager thread could be a VirtualThread Changes: https://git.openjdk.org/jdk/pull/28395/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28395&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8372159 Stats: 290 lines in 8 files changed: 264 ins; 15 del; 11 mod Patch: https://git.openjdk.org/jdk/pull/28395.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/28395/head:pull/28395 PR: https://git.openjdk.org/jdk/pull/28395
