public class AsyncStateMachine
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.
 READ_WRITE_OP    - Performing an asynchronous read or write.
 MUST_COMPLETE    - ServletRequest.startAsync() followed by complete() have
                    been called during a single Servlet.service() method. The
                    complete() will be processed as soon as the request
                    finishes.
 COMPLETE_PENDING - ServletRequest.startAsync() has been called and before the
                    request in which that call was had finished processing,
                    complete() was called for a non-container thread. The
                    complete() will be processed as soon as the request
                    finishes. This is different to MUST_COMPLETE because of
                    differences required to avoid race conditions during error
                    handling.
 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    - ServletRequest.startAsync() followed by dispatch() have
                    been called during a single Servlet.service() method. The
                    dispatch() will be processed as soon as the request
                    finishes.
 DISPATCH_PENDING - ServletRequest.startAsync() has been called and before the
                    request in which that call was had finished processing,
                    dispatch() was called for a non-container thread. The
                    dispatch() will be processed as soon as the request
                    finishes. This is different to MUST_DISPATCH because of
                    differences required to avoid race conditions during error
                    handling.
 DISPATCHING      - The dispatch is being processed.
 MUST_ERROR       - ServletRequest.startAsync() has been called followed by an
                    I/O error on a non-container thread. The main purpose of
                    this state is to prevent additional async actions
                    (complete(), dispatch() etc.) on the non-container thread.
                    The container will perform the necessary error handling,
                    including ensuring that the AsyncLister.onError() method
                    is called.
 ERROR            - Something went wrong.

                           |-----«-------------------------------«------------------------------|
                           |                                                                    |
                           |      error()                                                       |
 |-----------------»---|   |  |--«--------MUST_ERROR---------------«------------------------|   |
 |                    \|/ \|/\|/                                                            |   |
 |   |----------«-----E R R O R--«-----------------------«-------------------------------|  |   |
 |   |      complete() /|\/|\\ \-«--------------------------------«-------|              |  |   |
 |   |                  |  |  \                                           |              |  |   |
 |   |    |-----»-------|  |   \-----------»----------|                   |              |  |   |
 |   |    |                |                          |dispatch()         |              |  ^   |
 |   |    |                |                         \|/                  ^              |  |   |
 |   |    |                |          |--|timeout()   |                   |              |  |   |
 |   |    |     post()     |          | \|/           |     post()        |              |  |   |
 |   |    |    |---------- | --»DISPATCHED«---------- | --------------COMPLETING«-----|  |  |   |
 |   |    |    |           |   /|\/|\ |               |                | /|\ /|\      |  |  |   |
 |   |    |    |    |---»- | ---|  |  |startAsync()   |       timeout()|--|   |       |  |  |   |
 |   |    ^    ^    |      |       |  |               |                       |       |  ^  |   |
 |   |    |    |    |   |-- \ -----|  |   complete()  |                       |post() |  |  |   |
 |   |    |    |    |   |    \        |     /--»----- | ---COMPLETE_PENDING-»-|       ^  |  |   |
 |   |    |    |    |   |     \       |    /          |                               |  |  |   |
 |   |    |    |    |   ^      \      |   /           |                    complete() |  |  |   |
 |  \|/   |    |    |   |       \    \|/ /   post()   |                     /---»-----|  |  ^   |
 | MUST_COMPLETE-«- | - | --«----STARTING--»--------- | ------------|      /             |  |   |
 |  /|\    /|\      |   |  complete()  | \            |             |     /   error()    |  |   ^
 |   |      |       |   |              |  \           |             |    //---»----------|  |   |
 |   |      |       ^   |    dispatch()|   \          |    post()   |   //                  |   |
 |   |      |       |   |              |    \         |    |-----|  |  //   nct-io-error    |   |
 |   |      |       |   |              |     \        |    |     |  | ///---»---------------|   |
 |   |      |       |   |             \|/     \       |    |    \|/\| |||                       |
 |   |      |       |   |--«--MUST_DISPATCH-----«-----|    |--«--STARTED«---------«---------|   |
 |   |      |       | dispatched() /|\   |      \               / |   |        post()       |   |
 |   |      |       |               |    |       \             /  |   |                     |   |
 |   |      |       |               |    |        \           /   |   |                     |   |
 |   |      |       |               |    |post()  |           |   |   |                     ^   |
 ^   |      ^       |               |    |       \|/          |   |   |asyncOperation()     |   |
 |   |      |       ^               |    |  DISPATCH_PENDING  |   |   |                     |   |
 |   |      |       |               |    |  |post()           |   |   |                     |   |
 |   |      |       |               |    |  |      |----------|   |   |»-READ_WRITE_OP--»---|   |
 |   |      |       |               |    |  |      |  dispatch()  |            |  |  |          |
 |   |      |       |               |    |  |      |              |            |  |  |          |
 |   |      |       |post()         |    |  |      |     timeout()|            |  |  |   error()|
 |   |      |       |dispatched()   |   \|/\|/    \|/             |  dispatch()|  |  |-»--------|
 |   |      |       |---«---------- | ---DISPATCHING«-----«------ | ------«----|  |
 |   |      |                       |     |    ^                  |               |
 |   |      |                       |     |----|                  |               |
 |   |      |                       |    timeout()                |               |
 |   |      |                       |                             |               |
 |   |      |                       |       dispatch()           \|/              |
 |   |      |                       |-----------«-----------TIMING_OUT            |
 |   |      |                                                 |   |               |
 |   |      |-------«----------------------------------«------|   |               |
 |   |                          complete()                        |               |
 |   |                                                            |               |
 |«- | ----«-------------------«-------------------------------«--|               |
     |                           error()                                          |
     |                                                  complete()                |
     |----------------------------------------------------------------------------|