stop http server safely

Signed-off-by: Shizuo Fujita <fujita@clear-code.com>

lib/fluent/plugin_helper/http_server/server.rb

@@ -40,6 +40,8 @@ def initialize(addr:, port:, logger:, default_app: nil, tls_context: nil)
  @uri = URI("#{scheme}://#{@addr}:#{@port}").to_s
  @router = Router.new(default_app)
  @server_task = nil
+ @server_task_queue = Thread::Queue.new
+
  Console.logger = Fluent::Log::ConsoleAdapter.wrap(@logger)
 
  opts = if tls_context
@@ -67,17 +69,17 @@ def start(notify = nil)
  if notify
  notify.push(:ready)
  end
+
+ @server_task_queue.pop
+ @server_task.stop
  end
 
  @logger.debug('Finished HTTP server')
  end
 
  def stop
  @logger.debug('closing HTTP server')
-
- if @server_task
- @server_task.stop
- end
+ @server_task_queue.push(:stop)
  end
 
  HttpServer::Methods::ALL.map { |e| e.downcase.to_sym }.each do |name|