What causes players to desync?

[Marshmalo]

Hi there, we have a desync issue with a map we are working on, we are having a look at the triggers but we cant see what is causing it. I have to admit I had no idea that players could desync due to trigger bugs but clearly something is going wrong.

There are a number of triggers that play sounds for specific players using costum scripts, could this be what is causing it?

 

[EmoBrother]

I don't think play sound for specific player will cause that.
As far as I know, create quest (it won't cause that if u use Enable/Disable), pause game for a specific player will cause desync.You can find these in Tutorial, GetLocalPlayer

 

[SeriousEnemy]

Mostly the command If GetLocalPlayer() == Player(whatever) then causes desyncs, when used wrong.
But it depents what you change in those local blocks.

You are just allowed to insert non-game changing stuff here.
For example:

local sound s
if GetLocalPlayer() == GetTriggerPlayer() then
     set s = Your sound path...
     call PlaySound(s)
endif

This could cause desyncs.
The wrong part in this script is set s = ...

 

[Marshmalo]

Oh that has to be it! We use local player function quite alot! I will direct my co-map maker (goblinkingsp) to this as a matter of urgency.

 

[Arhowk]

Mostly the command If GetLocalPlayer() == Player(whatever) then causes desyncs, when used wrong.
But it depents what you change in those local blocks.

You are just allowed to insert non-game changing stuff here.
For example:

local sound s
if GetLocalPlayer() == GetTriggerPlayer() then
     set s = Your sound path...
     call PlaySound(s)
endif

This could cause desyncs.
The wrong part in this script is set s = ...

no, the wrong part is where you dont set s outside of the block than play the sound inside the block

 

[Goblinkingsp]

Upon discussing this issue with the gremlins inside of our map, I can confirm I will be reviewing this process.

 

[Marshmalo]

I placed a "Display message to all players" action just after get local player in order to display the message to just one single player, could that be which is causing the desync? Is this not to be used in a get local player fuction?

no, the wrong part is where you dont set s outside of the block than play the sound inside the block

I don't know what that means but Goblinkingsp do you understand that?

 

[UgoUgo]

I don't know what that means but Goblinkingsp do you understand that?

Im not a JASS pro, but I think Arhowk meant that the actual script should be:

local sound s
set sound s =  Your sound path
if GetLocalPlayer () == GetTriggerPlayer() then
        call PlaySound(s)
endif

Or Im wrong, Im learning too.

 

[Arhowk]

Im not a JASS pro, but I think Arhowk meant that the actual script should be:

local sound s
set sound s =  Your sound path
if GetLocalPlayer () == GetTriggerPlayer() then
        call PlaySound(s)
endif

Or Im wrong, Im learning too.

no

local sound s = null
if GetLocalPlayer () == GetTriggerPlayer() then
        set s = your sound
endif
call PlaySound(s)

not that good with sounds but i think itd be safer to set the volume to 0% rather than setting the sound to null

 

[MortAr]

call StartSoundForPlayerBJ (<Player>, <Sound>)
If you don't want to bother with GetLocalPlayer()

call DisplayTimedTextToPlayer (<Player>, X, Y, Time, "<Message>")
To show a text to one player only.

Desync may be caused also by loading too many triggers at one time or a single trigger running too many actions really quick.

 

[Arhowk]

call StartSoundForPlayerBJ (<Player>, <Sound>)
If you don't want to bother with GetLocalPlayer()

call DisplayTimedTextToPlayer (<Player>, X, Y, Time, "<Message>")
To show a text to one player only.

Desync may be caused also by loading too many triggers at one time or a single trigger running too many actions really quick.

Oh i guess blizzard allows that... oh well. My way is correct for everything else -_-

function StartSoundForPlayerBJ takes player whichPlayer, sound soundHandle returns nothing
    if (whichPlayer == GetLocalPlayer()) then
        call StartSound(soundHandle)
    endif
endfunction

 

[T. D. W.]

if i can ask a question too about this topic: does using If (Player == GetLocalPlayer) then with a special effect will cause desync?
If not, how icefrog does it in dota?????

 

[Xonok]

if i can ask a question too about this topic: does using If (Player == GetLocalPlayer) then with a special effect will cause desync?
If not, how icefrog does it in dota?????

Special effects don't cause desyncs.

 

[T. D. W.]

Special effects don't cause desyncs.

ok ty

 

[WaterKnight]

local sound s
if GetLocalPlayer() == GetTriggerPlayer() then
     set s = Your sound path...
     call PlaySound(s)
endif

This could cause desyncs.
The wrong part in this script is set s = ...

By itself, no.

not that good with sounds but i think itd be safer to set the volume to 0% rather than setting the sound to null

While setting it to null for playing does not make a difference, there are functions like GetSoundIsPlaying that would of course provide different results when starting the sound locally.

Desync may be caused also by loading too many triggers at one time or a single trigger running too many actions really quick.

Never had. But of course you could locally hit the op limit, which should be avoided either way.

Special effects don't cause desyncs.

False. Effects belong to the shared object id pool that should be in sync. Create them with an async model instead ("").

 

[Xonok]

False. Effects belong to the shared object id pool that should be in sync. Create them with an async model instead ("").

The special effects themselves don't desync, what do are the strings used to create them, afaik.

 

[WaterKnight]

Nope. And the string table desync is a myth to me or only appears in special cases. Same with the long-rumored sync of global variables.

 

[Xonok]

Nope. And the string table desync is a myth to me or only appears in special cases. Same with the long-rumored sync of global variables.

I think it's about initialization.

Theory:
The first time a variable is initialized it is marked as "existant". (Probably by the existance of a value)
If you try to reference an unexistant variable, then it does something differently that affects the game. Thus, a desync.
There's a similar problem with trying to use i = i + 1 if i has not been initialized to a number. Simply put - variables reference to values. If they don't have a referenced value, then they are considered "nonexistant".

 

[Dr Super Good]

Anything that causes the internal synchronous game state to become different between two or more clients.

A very easy example is the use of terrain deformations from standard Blizzard spells (Shockwave, War Stomp) causing different terrain node heights depending on client platform and settings. The most common result is a split between Mac and Windows users.

 

[WaterKnight]

You should not read an unset variable. That's for sure. The trigger execution would halt. Nor should you call functions with invalid parameters.

I do not see the connection to what you quoted. The single variables do not have to be kept in sync let alone create extra traffic.

A very easy example is the use of terrain deformations from standard Blizzard spells (Shockwave, War Stomp) causing different terrain node heights depending on client platform and settings. The most common result is a split between Mac and Windows users.

Only if you use the GetLocationZ function, which may be async even with equal os and graphic options. Wc3 itself nowhere relies on the z dimension gameplay-wise.

 

[MortAr]

I've personally experienced a desync by loading too many actions within 0.3 seconds, causing all players except the host one to disconnect.

 

[Xonok]

You should not read an unset variable. That's for sure. The trigger execution would halt. Nor should you call functions with invalid parameters.

I do not see the connection to what you quoted. The single variables do not have to be kept in sync let alone create extra traffic.

What I mean is that the engine obviously has its own automated ways of sharing variables based on some criteria. However, an array doesn't immediately take the space it would take if it was filled with nulls.
Thus I assume that the variables are actually created on first initialization.
How should it relate? Well if a client tries to reference variables that don't exist for all parties, then it will desync. Seems quite obvious.
So the problem isn't about reading unset variables, but trying to manipulate nonexistant variables. After all, reading unset variables already has some error handling(returning 0 if something is wrong).

 

[WaterKnight]

Well if a client tries to reference variables that don't exist for all parties, then it will desync. Seems quite obvious.
So the problem isn't about reading unset variables, but trying to manipulate nonexistant variables.

No, the other parties do not need to know your variables and this would be overkill. There are even object types you can instantiate on single clients, those that are handled locally. If you avoid all possible false signals, you can even do more like starting different triggers on different clients.

However, as for variables, you should pay attention to the reference-counting of agent object types. A unit does not release its id before all pointers to it are gone. Since you should not desync the shared id pool, you have to refrain from resetting the last pointer in an async pattern. Maybe that is why global variables are said to be checked because the concept of nullifying variables in order to avoid memory leaks is mostly taught targeting local ones only since globals are recycled in usage/not dynamic.

 

[Dr Super Good]

Reading a variable that has not been initialized will cause a thread crash as the internal hashtable lookup will fail (yes, each time WC3 reads a variable it looks it up in an internal hashtable).

 

[Marshmalo]

Hey guys, well after messing about alot with my map it turns out players are STILL desyncing, in my latest test players desynced within a few seconds of map startup, I have looked at my triggers and I can't understand whats causing this.

If I gave one of you an unprotected version of my map would you be able to look at it and fix the triggers?

Its my LORDAERON: The Aftermath map (see link in sig).

If someone could fix this I would be eternally grateful as this is really holding up development of this map! It is an azeroth wars style map so pretty big though! Please can anyone help?

 

[BloodDrunk]

    if GetLocalPlayer() == GetTriggerPlayer() then
    call StopMusicBJ( false )
    call PlayMusicBJ( gg_snd_Orc1 )
    endif
endfunction

I use this for music... no desyncs, everything works properly

 

[Marshmalo]

Would anyone look at my map for me?

Players desynced at start of map and there are no call function triggers at startup so don't understand why this is happening.