ASF Bug 57592 – numberwriter example: Response status 500, asyncOperation() not valid for request with state DISPATCHED Correctly handle the case where an AsyncContext is used for non-blocking I/O and is completed during a write operation.

First noted this when testing 8.0.20 release candidate, but this is also reproducible with 8.0.18 and 8.0.17.
http://markmail.org/message/rkkdl6publsievvi

Steps to reproduce:
1) go to /examples/servlets/nonblocking/numberwriter with a web browser
2) look into access log
Expected: status 200
Actual: status 500 for APR, NIO, NIO2. (BIO is OK)

This issue depends on timing. E.g. it reproduces for me consistently with HTTP connector, but not HTTPS connector. It does not reproduce in some other configurations.

3) Add the following line to logging.properties to enable FINE logging for Coyote:
org.apache.coyote.level=FINE

https://bz.apache.org/bugzilla/show_bug.cgi?id=57592
http://svn.apache.org/r1664661