Graceful shutdown and restart

Shadowsocks supports graceful shutdown like nginx.

You can send SIGQUIT to sslocal or ssserver process. The process closes listening sockets but still serves alive connections, allowing you to start a new process on the same port. When all connections on the old process are closed, it will then exit.

If you are using workers, send SIGQUIT to master process.

On Windows, please use SIGTERM instead.