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From Remy Maucherat <r...@apache.org>
Subject Re: APR, WebSocket and Servlet 3.1 NIO refactoring
Date Tue, 15 Jan 2013 16:15:37 GMT
On Tue, 2013-01-15 at 13:29 +0000, Mark Thomas wrote:
> Hi,
> 
> I think I am going to need to refactor the APR Poller code. Before I get
> to far down that road I wanted to get a sanity check from those that
> understand the APR/native connector better than I do.
> 
> The main problem:
> - I need to be able to update the flags for a socket current in the
> poller. For example, adding FLAGS_WRITE to a socket that currently has
> FLAGS_READ
> 
> Side issues:
> - APR connections don't track number of HTTP keep-alives left (it gets
> reset every time the socket goes back to the Poller)
> - Currently we have two completely separate sets of Pollers. Once for
> Comet and one for non-Comet.
> 
> The reasoning for the refactoring:
> 
> 1. Sockets should only be added to a pollset once.
> 2. Because of 1) to update the flags the socket needs to be removed from
> the pollset and re-added with the new flags.
> 3. Currently, we have no record of which Poller a socket is registered
> with. This makes 2) more expensive as we have to iterate through the
> Pollers to find the socket. Tracking the current poller used by a socket
> would make 2) a cheaper operation.
> 4. Implementing 3) requires maintaining a mapping from socket to
> SocketWrapper (like KeyAttachment does in NIO)
> 5. A simple Map of Socket->SocketWrapper should give us what we need.

I had to solve each of these issues in the web container of JBoss.
Although this is not going to be quite 100% compatible with Tomcat, it
is very similar.

I recommend looking at the branch that is in AS 7 trunk:
http://anonsvn.jboss.org/repos/jbossweb/branches/7.2.x/

> In addition to enabling me to continue with the Servlet 3.1 NIO work,
> the other advantages to the proposed refactoring are:
> - Will be able to eliminate the CometPollers since the SocketWrapper
> knows if a request is Comet or not.
> - Proper tracking of HTTP keep-alive requests left per connection.
> 
> If anyone can see a good reason not to start down this path, please
> speak up.

With APR, I would keep a separate poller for events (called comet in
Tomcat) and keepalive, the code is rather different.

Rémy



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