class Puma::Launcher

def write_pid

to a file.
If configured, write the pid of the current process out

def write_pid
  path = @options[:pidfile]
  return unless path
  cur_pid = Process.pid
  File.write path, cur_pid, mode: 'wb:UTF-8'
  at_exit do
    delete_pidfile if cur_pid == Process.pid
  end
end