Correct. If you're Google, and can devote a team to build and maintain a webserver specifically designed to handle Comet, then you can use Comet.

If you're small and need to use off-the-shelf tech to get your thing up and running quickly, you're still best off going with Polling today.

A quick example would be to look at Thinkature vs. Twiddla. They had a team of two, one of which spent an entire year building a web server from the ground up so that they could use Comet. Twiddla only has me as a developer, and I'd rather spend my time improving the product, so we use Polling.

One year later, Twiddla has a ~300ms lag between when you draw a line and when it appears on a remote screen, whereas Thinkature is out of business. I don't think it's that black and white of a tradeoff, but hopefully you see the thrust of what I'm saying.

One day soon, there will be a mod_comet for Apache, or IIS 9 with Comet support built in. That will be the day it makes sense for small, lean teams to build a business around it.

I spent a year or so building my own comet server. Because I did that, I'm able to finely control every single element of it. I know in absolute detail how it works, what sucks, what rocks, etc.

Obviously you have to decide how important things are to your success, and decide if you should build it yourself, or use some existing code out there. For me, it was a no brainer decision.

mod_comet is missing the point. Apache is the issue when using comet. Apache is what needs fixing/replacing.

If Mibbit was using polling, my bandwidth bill would be through the roof.

Sounds like we're in agreement then.

If you want to use Comet today, you need to build something custom, and it will probably take a lot of time, but it will pay off as you describe in terms of flexibility.

Im cetainly not, iserve, yaws and mochiweb are all "off the shelf" web servers that can handle comet pretty well. I cant believe erlang has the monopoly on lightweight web servers either.

Fair enough. Like you said elsewhere on this thread, we're down to defining "off the shelf" now, so I think we should probably call it a day.

  http://code.google.com/p/mochiweb/issues/detail?id=2
  http://www.google.com/search?q=comet+site:http://yaws.hyber.org/
  http://frihjul.net/iserve

Those are the available docs for the technologies you mentioned. Yaws has some real documentation, but not for its Comet implementation. The others give you some source code and tell you to have fun.

So yeah, it's right there on the shelf (how 'bout we settle on "perched on the edge of the shelf?") I'm just not smart enough (or motivated enough) to actually use any of it.

I still kinda disagree with your point though. There's nothing particularly unique to comet here.

If you want to make anything the best it can be, you need to build it custom, and it will probably take a lot of time, but it will pay off...

or you could not use general purpose web servers for edge cases, mochiweb for example is pretty great at handling comet requests.

axod does mibbit by himself, we(hypernumbers) use comet and are a small team, meebo used comet from the start.

there really isnt much of a barrier with comet, it was actually a hell of a lot easier than the flash sockets setup I implemented before it.

* probably worth mentioning facebook used mochiweb for their chat (off the shelf), I do find it hard to believe the only lightweight webservers around are in erlang

Wouldn't you say that any application thinking of using Comet would by definition be an edge case?

But yeah, I'd disagree that the barrier to Comet is low. The natural thing to compare it to is HTTP Polling, which has no barrier whatsoever beyond knowing about window.setInterval(); (is it correct to end a sentence containing code with a semicolon?:)

Twiddla went from concept to launch in ten hours, largely because I didn't need to spend any time thinking about how to handle communications. The intention was to replace Polling with Comet at some point in the future, but you know what? It just isn't anywhere near as slow or problematic as I was expecting.

Back to my original point, there are a lot of smart people (such as yourself) working on this problem. Before the year is out, I suspect that somebody will have a good, proven, out-of-the-box Comet server that you can simply drop your application onto. That's the day I'm waiting for.

heh the point of all 3 of my comments is that there is a good, proven, out-of-the-box* comet server. mochiweb, I havent tested but I would imagine iserve and yaws handle themselves similarly well.

* depending on your definition of out-of-the-box, mochiweb doesnt actually enforce any "protocol" for handling comet for you, those are application specific and reasonably trivial to code.

* I also forgot about erlycomet, which is built on mochiweb, and is a straight out of the box comet server

axod is a team of one, and mibbit apparently uses "Comet".