I’ve found the Servlet 3.0 Asynchronous API tricky to implement correctly and helpful documentation to be sparse. After a lot of trial and error and trying many different approaches, I was able to find a robust solution that I’ve been very happy with. When I look at my code and compare it to yours, I … Read more
A recent post by Jacques Mattheij, referencing your very question, claims that although HTTP was designed as a synchronous protocol, the implementation was not. In practise the browser (he doesn’t specify which exactly) accepts answers to requests have not been sent yet. On the other hand, if you are looking to something less hacky, you … Read more
I’d take a look at evserver (http://code.google.com/p/evserver/) if all you need is comet. It “supports [the] little known Asynchronous WSGI extension” and is build around libevent. Works like a charm and supports django. The actual handler code is a bit ugly, but it scales well as it really is async io. I have used evserver … Read more
That tech is known as “comet”, but also as “server push”, “reverse ajax”, etc. It’s about pushing data from the server to the browser, keeping an http connection alive. Find more info on it on the wikipedia article (English version). Also here’s a pretty good presentation with Joe Walker from DWR, where he talks about … Read more
Agreeing/expanding what has already been said, I don’t think FastCGI will solve the problem. Apache Each request into Apache will use one worker thread until the request completes, which may be a long time for COMET requests. This article on Ajaxian mentions using COMET on Apache, and that it is difficult. The problem isn’t specific … Read more
Just for the sake of argument. Both are http request (xhr), and its at least partially untrue it uses more server resources (depends totally on technology, will explain later). Short polling. Lot of request that are processed as they come on server. Creates a lot of traffic (uses resources, but frees them as soon as … Read more
Comet is challenging to scale with IIS because of comet’s persistent connectivity, but there is a team looking at Comet scenarios now. Also look at Aaron Lerch’s blog as I believe he’s done some early Comet work in ASP.NET.
I wrote the plugin mentioned by Till. The plugin is an implementation of the Bayeux protocol and currently supports long-polling (local server via AJAX) and callback-polling (remote server via XSS). There is a Bayeux implementation for Python called cometd-twisted that I have heard my plugin works with, but I have not verified this. I have … Read more
Yes, what you’re looking for is COMET http://en.wikipedia.org/wiki/Comet_(programming). Other good Google terms to search for are AJAX-push and reverse-ajax.
There are more differences than the ones you have identified. Duplex/directional: Uni-directional: HTTP poll, long poll, streaming. Bi-direcitonal: WebSockets, plugin networking In order of increasing latency (approximate): WebSockets Plugin networking HTTP streaming HTTP long-poll HTTP polling CORS (cross-origin support): WebSockets: yes Plugin networking: Flash via policy request (not sure about others) HTTP * (some recent … Read more