fillInterested() is called.
This is needed to avoid race conditions where fillInterested()
triggers a new thread entering onFillable() and acquiring a new buffer
while the previous thread is releasing the previous buffer.
Now instead of having the channel to dispatch when it detects that it
has to call the application (upon receiving a HEADERS frame, or upon
a push "fake" request), now the whole mechanism is controlled by an
ExecutionStrategy.
This is an initial recyling of the channel. The pool is a concurrent linked list, but it may be better to use an array backed list/stack that can easily enforce a maximum pool size.
The pool is currently on the session listener, when it really should be on the HTTP2ServerConnection, but more refactoring is needed for that.
Also the pool is currently inaccessible to the push mechanism
RequestLog can now be set on the HttpChannel and is called during the onCommitted callback.
The RequestLog may be set either on the server or via an updated RequestLogHandler that can
be applied to a specific context.
The HttpContent class has been reworked to store HttpField instances, we may be generated on
demand or instances of PreEncodedHttpField.
The encoding of HTTP2 fields has been generalized to handle both indexed and literal fields, selected
by header enum set.
Default servlet and response classes have been cleaned up in how they set response headers.
Introduced parameter "dispatchIO" in the relevant factories so that
they can be configured by users and connections will be created
taking into account this parameter.
For less configurable connection factories, this parameter is
currently hardcoded to either true or false depending on the case.
For example, ALPN and NPN connections have it to false, since they
don't do any blocking operation in onFillable().
Fixed by ensuring that when a failure happens, either by catching an
exception or by failing a callback, we always call completed() and
abort the channel (via new method terminate()).
Introduced ResetException, and using it when failing frames of streams
that have been reset already.
HttpTransportOverHTTP2.abort(Throwable) checks for this exception and
does not close the connection.
