question from servlet spec

From Java Spec/*******
Multiple servlets executing request threads may have active access to a single
session object at the same time.
*********************/
<b>please correct my understanding of the abave stmt<b>
In an distributed env...all the threads in the service method share the same sesion. So we haev to synchronize the session variable

hi,
to make things easier, first take distributed env out of consideration. lets see why a session object is accessible to mutiple threads. we know session is built on application level. it's easy to see a session object is accessable for all requests in the application.
in a distributed enverioment, session management is more complex. i think info about a session object should be kept in an external storage, like ejb or database. note that synchronization is only effective in a single VM.