BaseServer.shutdown() waits for serve_forever() to return. The SIGINT /
SIGTERM handlers called it directly, and signal handlers run on the same
thread that is executing serve_forever(), so the server could never exit:
the process hung until SIGKILL and the client was never closed.
Ask a helper thread to call shutdown() and move server_close()/client.close()
into a finally block after serve_forever() returns. Add an in-process test
and a subprocess test that fires SIGALRM while serving on the main thread.
Co-authored-by: qiye.sjh <shijiahao_0802@youzan.com>
Co-authored-by: Claude Code <noreply@anthropic.com>
alvinfei