Multiplayer Desync

[dipwood]

We have been playing games regularly for a little while now with no problems.

Suddenly, today, we experienced a crippling desync that would not go away no matter how many times we saved and reloaded the game. So, we gave up and started a new game. Then, in the new game, it occurred again, and we found something that could be a coincidence, could be vital.

Basically, in both instances I was the only one to choose a melee special ship, and in both instances the desync occurred when I moved out a fleet of 200-300 melee ships through a wormhole to an enemy system. It happened right as all my ships popped out in the other system. The first game, I had vampires. The second: Cutlasses. Nothing we could do would alleviate this. I included the savegame where the desynch happened.

The host was saying that the desync was lighting up to one player, and every time he rejoined we got a couple seconds of gameplay before it went again. We were playing with this person fine all last week with no problems.

[x4000]

Thank you so much for sending this! Sorry to hear of your troubles, but I am excited by how reproducible the issue is for you. We were already aware there was a desync somewhere, but it was just an obscure thing that we could not reproduce and that only one other group of players was reporting. We will take a look at your save today and see if that doesn't help us narrow it down; sounds like the melée ships might have something to do with it, as you say.

If that isn't it, then we may have some other questions about exactly what you were doing. Any new features you might have been using, that would thus help us narrow it down further. But my hopes are high for this savegame, I really appreciate it. Apologies again for the inconvenience, though -- I know how frustrating that is.

[x4000]

Hi dipwood,

I've been testing with this save that you posted, and I'm unable to replicate the desync in either version 3.144 or 3.120 of the game.  I notice that you're playing on 3.120, which is unfortunate for us because that means your desync is happening in the current official version of the game, and so it must be longer-standing than we thought.  We'll have to broaden our search for this in terms of what code diffs we are looking at, clearly.

But at the moment I'm simply not able to duplicate this specific desync, which makes it all but impossible to track down.  Is there any more information you can provide?  Things that would be particularly useful:

1. What steps should I be taking in the savegame you provided in order to create the desync?

2. What kind of computers are each of you running?  Mainly what OS and if each is 32 or 64 bit is all that matters.

3. When the game desyncs, which players does the host see desync next to?  Was it you, or THEBOSS, or both?

4. If it was just a single person in #3, what was that person doing when the desync happened?  Were they looking at a specific system?  Doing a specific kind of action?  If it was not a single person in #3, then same questions but for the host -- what was he doing, etc?

5. If another desync occurs, then having every player save a copy of the game while it is frozen there in desync-state, and then all posting the different saves, would be really helpful in tracking that down.  That lets us look at the three saves and compare them to see what actually is different in them.  That doesn't always lead to anything, but it can help.

Any info you can provide is much appreciated!  Thanks again for your patience and help with this.

[keith.lamothe]

Does the service-pack-level of the .NET install matter too?  Or is that an older thing?

[x4000]

Yes, that will cause desuncs at random if everyone is not on sp1 of .net 3.5.

[dipwood]

1. I don't know. It's already desynced at that point.

2. I'm using 32-bit XP, I don't know what they're using.

3. The host, Justin, sees THEBOSS as desynced only.

4. I don't know. I don't think they were looking at the system I was attacking at that particular moment.

5. We're gonna try again tomorrow.

Maybe this can help: Both of them, Justin and THEBOSS, are on the same network. In previous games we had a different host. When we play again tomorrow I'll try hosting (I'll have to use hamachi/Tunngle due to some sort of block in the cable modem (not router) I can't do anything about).

[x4000]

Okay, thanks for the info, I really appreciate it.  In our other desync thread, we have a serious lead on what is causing their one. It seems to be related to engineers assisting starship constructors in some really specific circumstances.  I don't know if that's the same issue you are having, or not, but hopefully there's not multiple desyncs here.  If you get another desync tomorrow, then I could use the following:

1. The last autosave from before the desync (it ought to be 10 minutes before the desync at absolute most, at the default settings).

2. The savegames from all three of the players right after the desync.

3. Which player(s) the host sees as desynced, if it's THEBOSS again or what, and what he was doing and looking at at the time.

4. What the OS version and 32/64 bit levels of the other players are.


Hopefully we'll have it figured out before then and none of that will be needed anyway, but these desyncs are absolutely the trickiest things to hunt down in game programming, and this one is particularly a challenge for some reason.  Thanks again!

[x4000]

Okay, there is a new version out now here: http://arcengames.com/forums/index.php/topic,5466.0.html

The hope with this version is that either:

1. Hopefully the existing changes in that version will fix your desync.

2. If not, hopefully this version will cause your game to crash and give us a stack trace telling us exactly where there is a stack overflow, if that's what is causing your desync, which would then point us to the exact line of code we need to fix rather than leaving us in a sea of ambiguity as we are at the moment.

Hopefully #1 is true, and it just fixes your issue and that's the end of it!  Fingers crossed!