title: Should ServerEndpointConfig.Configurator instance be thread safe?
body: <p>I want to share some information between websocket connections. The shared data is a bit complex so I can not use <code>EndpointConfig.getUserProperties()</code>. I want to extend <code>ServerEndpointConfig.Configurator</code> and add my own data structures.(I don't want to override other methods such as <code>getEndpointInstance</code>). The question is should I use thread safe data structures? Or I can use any data structure and web socket container will guarantee that my instance of <code>ServerEndpointConfig.Configurator</code> will be accessed in safe manner.</p>