Thread A                                                   Thread B

|                                                          |
session.invalidate()                                       |
|                                                          |
+- StandardSession#invalidate()                            |
   |                                                       |
   +- StandardSession#expire()                             |
      |                                                    |
      +- StandardSession#expire(true)                      |
         |                                                 |
         if (expiring || !isValid) { } --> false           |
         |                                         	   |       
         synchronized(this) {                      	   |
           |                                       	   |
           ...                                     	   |
           |                                       	   |
           expiring = true;                        	   |
           |                                       	   |
           ... (many things happening)             	   session.invalidate()
           |                                       	   |
           |                                       	   +- StandardSession#invalidate()                 
           |                                       	      |
           |                                       	      StandardSession#expire()
           |                                       	      |
           |                                       	      +- StandardSession#expire(true)
           |                                       	         |
           |                                       	         if (expiring || !isValid) return; --> true
           |                                       	         |
           |                                       	   +-----+
           |                                       	   |
           |                                       	   session = request.getSession(true)
           |					   	   |                                 
           |                                       	   +- ApplicationHttpRequest#getSession(true)		       
           |					   	      |							       
           |					   	      if (crossContext) {  --> true			       
           |					   	        |						       
           |					   	        ...						       
           |					   	        | 						       
           |					   	        if (session != null && session.isValid()) { --> true   
           |					   	          |						       
           |					   	          return (session.getSession());		       
           |					   	          |						       
	   |					   	        }                                       	       
           |                                       	        |
           |                                       	      }
           |                                       	      |
           |                                       	   +--+
           |                                       	   |
           |                                       	   | // now session refers to the same object as befor an object in state "expiring"
           setValid(false)                         	   |
           |                                               |
           ...                                             |
           |                                               |
           expiring = false;                               |
           |                                               |
         } // end of synchronization block                 |                                                   
         |                                                 | // now session refers to an invalidated object
+--------+                                                 |