When the thread is writing to the response in
RECEIVED.onWritePossible(), the execution may stop because isReady()
returned false. In this case the buffer is partially written.
When there is partially written case:
1. The state will be changed from WRITING to RECEIVED
2. A check for "write possible" will be performed:
- If onWritePossible event has been already called by the web
container while in WRITING state then this check will trigger
RECEIVED.onWritePossible() because isReady() will be true and the
writing will continue.
- Otherwise the writing will be resumed when the web container sends
onWritePossible event.