PHP AJAX Multiplayer Game

I'm planning a relatively simple, online, multiplayer game and I'm stumped on what to use for player to player communication.

Game details:

• 6 Players
• Chat box
• 30 second rounds (intermissions)
• Time sync is important

Players select and action and at the end of the round, the action is performed, there is a brief intermission to detail actions and a new round begins.

I've determined to build this game entirely in JS and PHP (of course AJAX). I just don't know what I should use for the client to client communication - I initially planned on using constant 1/2 second AJAX calls to 开发者_JAVA技巧the PHP script using mySQL to store the game/user data, but I'm afraid that will be too slow and unpredictable.

I considered using something like a XML instead of mySQL and using something like the php fopen() function - what do you guys think about that?

I read in this question here, where the poster is considering using XMPP, could that be a good solution?

Should I go for a socket? Is that necessary for a game that doesn't require all that much data to be exchanged? What would be required to get this going?

Any suggestions on syncing the round time? Or is this something that I even really need to concern myself with?

I'm open to all suggestions and really appreciate any help I can get.

Go for Comet, you don't need sockets. Comet is a kind of reverse-AJAX. Works perfectly for p2p things like instant messenger, for example, because it pushes data to browser without browser needing to constantly poll the server. And there are many implementations for Comet in JS/PHP, just Google that. Then, as a backend, you could use MySQL or XML or whatever you want (but I would consider MySQL as a better solution, because XML is just a text file which needs to be opened, read, written and closed and the database is designed to be faster than that).

If you're determined to use PHP/JS/Ajax, then I would suggest you read about using the PHP usleep() function to delay returning the results of an ajax call until the server has something to say. This should result in much faster server to client communication.

I haven't done this myself, but I think the basic principle is that you can delay for 5 to 10 seconds per ajax call, performing a new call whenever one times out or is returned from the server with data.

Also, I would recommend a javascript framework (jQuery for example) to make the ajax calls more manageable.

I am also building a game with JS/PHP and here is my plan: have a plain text file on the server. Whenever the user does an action that needs to be sent to the server it sends an XMLHttpRequest to a php script, which appends the action to the file (for example, if a user launches a missile from Miami to Moscow it would write "launch Miami Moscow" to the file). To check for when the other person does something, you open an XMLHttpRequest on a different PHP script, and when the PHP script returns something, you record what it returned and reopen the connection. That PHP script checks for modifications to the file, and returns the file contents when it does change. Here is the PHP file that checks for changes:

<?php
#First, set infinite time limit
set_time_limit(0);
#record last modification time
$f1=filemtime('./nameoffile.txt');
#wait until the file changes
while($f1===filemtime('./nameoffile.txt'){
    #have a 10,000 microsecond break between each check so you do not use too much resources
    usleep(10000);
readfile('./nameoffile.txt');
?>

You may also want to look into HTML5 WebSockets. I do not use them and do not know if they work with PHP, but they seem interesting.