How to implement Server push / long polling / comet using PHP and Javascript

How can I implement the comet / server push design pattern using PHP and Javascript? Essentially what I would like is something like this:

• User clicks a 'submit' button
• Javascript shows a message like 'Process开发者_StackOverflowing 0 / 100 items'
• Whenever a new item is processed, the php / server pushes out an update, and the javascript changes the message to 'Processing 2/100 items, 3/100 items, and so on'.

How can I do this? Any links/info please?

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Comet with PHP has some tricky issues with scaling. An alternative would be a SaaS solution, such as WebSync On-Demand. (Disclaimer: I work there). That way you don't have to worry about any of the behind the scenes stuff, and you can just get your server-push functionality.

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There are a couple of very good examples at: How to implement comet with PHP

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Most of the services use the Client-initiated requests, but there's also Comet. There's a few articles out there on it.