How do I maintain an online users list?

Question

In a multiplayer JavaScript game client, is it a good idea to poll the server periodically to refresh online user list, or keep track of joined/left users? Is there a better option?

Answer 1

A combination of both strategies would likely yield the best results. Just keeping track of when user join/leave might not account for situations where the user is unexpectedly disconnected. A periodic poll would likely have to happen too often to get reasonably updated list of players joining and leaving.

So, update the list when a player joins or leaves and poll less periodically.

Answer 2

It depends is network traffic efficiency really important to you. If it is not you might have three actions in your server:

• connect - which will add user to a server list
• disconnect - which will delete user for a server list
• poll - which will periodically check all users alive status (simple ping with client app)

More complex but also better way is to use timers. Every user will have a separate timer when he joins. When the timer runs out, server will poll for his status.

• if he is alive server reset timer
• if he is not responding server will delete him from user list

It won`t generate as big lag as polling all users at once.

Edit:

actions for the client

• connect
• disconnect
• "ping" response

In other words, you are not polling server at all until server will ask you for alive status.