public class AsyncStateMachine<S>
extends java.lang.Object

Manages the state transitions for async requests.

 The internal states that are used are:
 DISPATCHED    - Standard request. Not in Async mode.
 STARTING      - ServletRequest.startAsync() has been called but the
                 request in which that call was made has not finished
                 processing.
 STARTED       - ServletRequest.startAsync() has been called and the
                 request in which that call was made has finished
                 processing.
 MUST_COMPLETE - complete() has been called before the request in which
                 ServletRequest.startAsync() has finished. As soon as that
                 request finishes, the complete() will be processed.
 COMPLETING    - The call to complete() was made once the request was in
                 the STARTED state. May or may not be triggered by a
                 container thread - depends if start(Runnable) was used
 TIMING_OUT    - The async request has timed out and is waiting for a call
                 to complete(). If that isn't made, the error state will
                 entered.
 MUST_DISPATCH - dispatch() has been called from a container thread. The
                 dispatch will be processed once processing control returns to
                 the container.
 DISPATCHING   - dispatch() has been called from a non-container thread. The
                 dispatch will be processed as soon as a container thread is
                 available.
 ERROR         - Something went wrong.

 |----------------->--------------|
 |                               \|/
 |   |----------<---------------ERROR
 |   |      complete()         /|\ | \                                                          
 |   |                          |  |  \---------------|                                         
 |   |                          |  |                  |dispatch()                               
 |   |                          |  |postProcess()    \|/                                        
 |   |                   error()|  |                  |                                         
 |   |                          |  |  |--|timeout()   |                                         
 |   |           postProcess()  | \|/ | \|/           |         auto                            
 |   |         |--------------->DISPATCHED<---------- | --------------COMPLETING<-----|         
 |   |         |               /|\  |                 |                 | /|\         |         
 |   |         |    |--->-------|   |                 |                 |--|          |         
 |   |         ^    |               |startAsync()     |               timeout()       |         
 |   |         |    |               |                 |                               |         
 |  \|/        |    |  complete()  \|/  postProcess() |                               |         
 | MUST_COMPLETE-<- | ----<------STARTING-->--------- | ------------|                 ^         
 |         /|\      |               |                 |             |      complete() |         
 |          |       |               |                 |             |     /-----------|         
 |          |       ^               |dispatch()       |             |    /                      
 |          |       |               |                 |             |   /                       
 |          |       |              \|/                |            \|/ /                        
 |          |       |----<----MUST_DISPATCH----<------|          STARTED
 |          |       |   auto              \                      /|  
 |          |       |                      \                    / |   
 ^          ^       ^                       \        dispatch()/  |    
 |          |       |                        \                /   |    
 |          |       |               |-------- \ -------------/    |auto
 |          |       |               |          \                  |   
 |          |       |               |           \                 |   
 |          |       | auto         \|/           \               \|/  
 |          |       |---<------DISPATCHING        \---------TIMING_OUT
 |          |                                   dispatch()    |   |
 |          |                                                 |   |
 |          |-------<----------------------------------<------|   |
 |                              complete()                        |  
 |                                                                |  
 |<--------<-------------------<-------------------------------<--|  
                                 error()