How to synchronize Timer

[caniko]

I am using Timer in my turnbased game, how do you synchronize the timer on the server with a timer on the client? Authoritatively, you could compare the start timestamp between A and B, and rectify the timer on the slave side; is there any better way?

[cBournhonesque]

Only ticks are guaranteed to be fully synchronized. In fact the client's simulation slightly speeds up/slows down to remain in sync with the server simulation, so I wouldn't trust Timer to run exactly the same on both.
Maybe I should provide a lightyear Timer that internally converts the duration to ticks?

[caniko]

Timer that internally converts the duration to ticks?

Can I use this for my turn based game? Yes. So, yes please.

This doesn't solve all the issue with time. You need to remember the one-way trip latency from the authority to the clients. Idea for solution: Provide the timestamp of when the "ticking" started, so that they can be in proper sync with respect to UTC.

I can help with testing when you make the PR, I really need this 🙏🏼

[cBournhonesque]

It would help to know the exact usecase and what kind of api you have in mind.

A client input on tick T is guaranteed to be read by the server when the server reaches tick T, so maybe you can start a timer for D ticks whenever the server receives the input.
In the opposite direction (server->client) it's a bit trickier. Maybe you can just run the Timer on the server, and the server sends a message to the client when the timer is done?

[caniko]

My usecase: The server triggers the timer for the turn; the clients get a view into the time remaining; we signal all clients when the time is up from the server.

A client input on tick T is guaranteed to be read by the server when the server reaches tick T, so maybe you can start a timer for D ticks whenever the server receives the input.

Yes, if you provide the mentioned "tick interface", or are the components for this already available?

In the opposite direction (server->client) it's a bit trickier.

Yes.

Maybe you can just run the Timer on the server, and the server sends a message to the client when the timer is done?

That is definitely what will happen, but I need a representation of the time remaining on the client side. Since the input is handled exactly on tick T, starting a timer for D ticks then ensures that the timer will expire exactly at tick T + D; this could be taken into account on the client side.

Considering timers are a component of many games in different genres, I would prefer this to be implemented on the lightyear side.

[cBournhonesque]

What about just creating a component that holds ms_since_epoch or something and simply replicating that component?
Or you could maybe register Timer directly in your protocol with a custom serialize/deserialize function that serializes ms_since_epoch

[caniko]

Yes, this removes a lot of the issues around synchronization at the cost of additional processing per tick. A small price to pay I guess 🤷🏼‍♂️

I will need ms_remaining, which can be computed by durantion - ms_since_epoch; I think this is the most useful data. Also, ms_since_epoch should be computed by T + D, and not T; T is unfair towards the clients. Note that the T + D will not work during async-turns, so it should be an opt-in feature.