Hibakeresés

While scripting you will often come across problems that are not immediately apparent. This page tries to point out some basic strategies to locate the error.

Debug console

MTA features a built-in debug console that shows debug messages output from MTA functions or from scripts. You can open it by typing debugscript x in console, while x is the debug level:

• 1: only errors
• 2: errors and warnings
• 3: errors, warnings and info messages

Thus, by typing debugscript 3 all messages are visible, that or level 2 are recommended for most occasions. You should have debugscript enabled most of the time you are testing your scripts, this will help you detect typos or other simple issues and solve them easily.

Example

This example snippet has two errors:

if (getPlayerName(player) == "Fedor")
	outputChatbox("Hello Fedor")
end

When the script this piece of code is in is tried to be loaded, debugscript will output something similiar to this:

INFO: Loading script failed: C:\<server path>\mods\deathmatch\resources\myResource\script.lua:15: 'then' expected near ´outputChatbox'

This means the script could not be parsed, because there was a syntax error. It shows the path of the script, so you can also see what resource it is in ('myResource' in this case) and of course the name of the script. After the filename it shows the line number and again after that what was wrong. Easy to solve now, we just forgot the 'then' keyword:

if (getPlayerName(player) == "Fedor") then
	outputChatbox("Hello Fedor")
end

Now the script will load fine and won't output any errors, until a player with the name 'Fedor' enters this section of the script. Then, debugscript will output:

ERROR: C:\<server path>\mods\deathmatch\resources\d\script.lua:15: attempt to call global 'outputChatbox' (a nil value)

This means the called function does not exist, which can be easily explained since the functions' name is outputChatBox (with a capital B):

if (getPlayerName(player) == "Fedor") then
	outputChatBox("Hello Fedor")
end

This is of course just an example, there are plenty of other messages and scenarios, but you should get the idea.

Server & client debug logging

Server

Navigate to: (MTA root folder)>server>mods>deathmatch

There are two nearly identical files:

• The local.conf is the settings for the "host game" shortcut in the main menu of MTA. This is a quick, easy, and temporary way of starting servers from inside the client. When the client is turned off the server will also turn off.

• The mtaserver.conf is used when "MTA Server.exe" is executed from (MTA root folder)>server. This runs the server in its own window, that does not need the client running. This is for long-term hosting.

Depending on which way you host, you will want to edit those files. The settings in question are:

<!-- Specifies the location and name of the debugscript log file. If left blank, server won't be saving this file. -->
	<scriptdebuglogfile>logs/scripts.log</scriptdebuglogfile> 
	
	<!-- Specifies the level of the debugscript log file. Available values: 0, 1, 2, 3. When not set, defaults to 0. -->
	<scriptdebugloglevel>0</scriptdebugloglevel>

You want to make sure you have a log name specified. Also you want to specify what level of errors will be logged. If it is 0 nothing will be logged. The levels were explained at the top of this article. If the logging level was changed to 3, then in this case all serverside script errors log to (MTA root folder)>server>mods>deathmatch>logs>scripts.log

Client

Navigate to: (MTA root folder)>server>clientscript.log

This file logs all clientside script errors. This is set to log by default, no setup required.

Debug strategies

There are several strategies that support finding errors, apart from going through the code of course. Most of them include outputting debug messages, with differing information depending on the situtation.

Useful functions

First of all some functions that may come in handy for debugging.

• outputDebugString or outputChatBox for outputting any information
• tostring() on a variable to turn it into a string, for example when it contains a boolean value
• getElementType to check an MTA Element for its type

Add debugmessages to check if, when or how often a section of code is executed

A typical example would be verify whether an if-section is executed or not. To do that, just add any message you will recognize later within the if-section.

if (variable1 == variable2) then
	outputDebugString("entered if")
	-- do anything
end

Another application would be to check when variable values are modified. First search for all occurences of the variable being edited and add a message just beside it.

Add debugmessages to check the value of a variable

Let's say you want to create a marker, but it doesn't appear at the position you expect it to be. The first thing you might want to do is check if the createMarker function is executed. But while doing this, you can also check the values being used in the createMarker function in one run.

outputChatBox("posX is: "..x.." posY is: "..y.." posZ is: "..z)
createMarker(x,y,z)

This would output all three variables that are used as coordinates for the marker. Assuming you read those from a map file, you can now compare the debug output to the desired values. The tostring() will ensure that the variables' value can be put together as a string, even if it's a boolean value for example.

Example

Imagine you created a colshape (collision shape) somewhere and you want a player to stay 10 seconds in it, then perform some action.

function colShapeHit(player)
	-- set a timer to output a message (could as well execute another function)
	-- store the timer id in a table, using the player as index
	colshapeTimer[player] = setTimer(outputChatBox,10000,1,"The player stayed 10 seconds in the colshape!")
end
addEventHandler("onColShapeHit",getRootElement(),colShapeHit)

function colShapeLeave(player)
	-- kill the timer when the player leaves the colshape
	killTimer(colshapeTimer[player])
end
addEventHandler("onColShapeLeave",getRootElement(),colShapeLeave)

When a player enters the colshape, debugscript outputs the following message:

ERROR: ..[path]: attempt to index global 'colshapeTimer' (a nil value)

This means you tried to index a table that does not exist. In the example above, this is done when storing the timer id in the table. We need to add a check if the table exists and if not create it.

function colShapeHit(player)
	if (colshapeTimer == nil) then
		colshapeTimer = {}
	end
	-- set a timer to output a message (could as well execute another function)
	-- store the timer id in a table, using the player as index
	colshapeTimer[player] = setTimer(outputChatBox,10000,1,"The player stayed 10 seconds in the colshape!")
end
addEventHandler("onColShapeHit",getRootElement(),colShapeHit)

function colShapeLeave(player)
	-- kill the timer when the player leaves the colshape
	killTimer(colshapeTimer[player])
end
addEventHandler("onColShapeLeave",getRootElement(),colShapeLeave)

Now we still get a warning when a player enters the colshape, waits for the message and leaves it again:

WARNING: [..]: Bad argument @ 'killTimer' Line: ..

Except for that (we will talk about that later) everything seems to work fine. A player enters the colshape, the timer is started, if he stays the message occurs, if he leaves the timer is killed.

A more inconspicuous error

But for some reason the message gets outputted twice when you stay in the colcircle while in a vehicle. Since it would appear some code is executed twice, we add debug messages to check this.

function colShapeHit(player)
	if (colshapeTimer == nil) then
		colshapeTimer = {}
	end
	-- add a debug message
	outputDebugString("colShapeHit")
	-- set a timer to output a message (could as well execute another function)
	-- store the timer id in a table, using the player as index
	colshapeTimer[player] = setTimer(outputChatBox,10000,1,"The player stayed 10 seconds in the colshape!")
end
addEventHandler("onColShapeHit",getRootElement(),colShapeHit)

function colShapeLeave(player)
	-- add a debug message
	outputDebugString("colShapeLeave")
	-- kill the timer when the player leaves the colshape
	killTimer(colshapeTimer[player])
end
addEventHandler("onColShapeLeave",getRootElement(),colShapeLeave)

Now we notice that both handler functions get executed twice when we are in a vehicle, but only once when we are on-foot. It would appear the vehicle triggers the colshape as well. To confirm this theory, we check the player variable that should contain a player element.

function colShapeHit(player)
	if (colshapeTimer == nil) then
		colshapeTimer = {}
	end
	-- add a debug message, with the element type
	outputDebugString("colShapeHit "..getElementType(player))
	-- set a timer to output a message (could as well execute another function)
	-- store the timer id in a table, using the player as index
	colshapeTimer[player] = setTimer(outputChatBox,10000,1,"The player stayed 10 seconds in the colshape!")
end
addEventHandler("onColShapeHit",getRootElement(),colShapeHit)

function colShapeLeave(player)
	-- add a debug message, with the element type
	outputDebugString("colShapeLeave "..getElementType(player))
	-- kill the timer when the player leaves the colshape
	killTimer(colshapeTimer[player])
end
addEventHandler("onColShapeLeave",getRootElement(),colShapeLeave)

The debug messages tell us that one of the player variables is a player, the other one a vehicle element. Since we only want to react when a player enters the colshape, we add an if that will end the execution of the function if it's not an player element.

function colShapeHit(player)
	if (colshapeTimer == nil) then
		colshapeTimer = {}
	end
	-- add a check for the element type
	if (getElementType(player) ~= "player") then return end
	-- add a debug message, with the element type
	outputDebugString("colShapeHit "..getElementType(player))
	-- set a timer to output a message (could as well execute another function)
	-- store the timer id in a table, using the player as index
	colshapeTimer[player] = setTimer(outputChatBox,10000,1,"The player stayed 10 seconds in the colshape!")
end
addEventHandler("onColShapeHit",getRootElement(),colShapeHit)

function colShapeLeave(player)
	-- add a check for the element type
	if (getElementType(player) ~= "player") then return end
	-- add a debug message, with the element type
	outputDebugString("colShapeLeave "..getElementType(player))
	-- kill the timer when the player leaves the colshape
	killTimer(colshapeTimer[player])
end
addEventHandler("onColShapeLeave",getRootElement(),colShapeLeave)

Now the script should work as desired, but will still output the warning mentioned above. This happens because the timer we try to kill when a player leaves the colshape will not exist anymore when it reached the 10 seconds and is executed. There are different ways to get rid of that warning (since you know that the timer might not exist anymore and you only want to kill it if it is there). One way would be to check if the timer referenced in the table really exists. To do this, we need to use isTimer, which we will use when we kill the timer:

if (isTimer(colshapeTimer[player])) then
	killTimer(colshapeTimer[player])
end

So the complete working code would be:

function colShapeHit(player)
	if (colshapeTimer == nil) then
		colshapeTimer = {}
	end
	-- add a check for the element type
	if (getElementType(player) ~= "player") then return end
	-- add a debug message, with the element type
	outputDebugString("colShapeHit "..getElementType(player))
	-- set a timer to output a message (could as well execute another function)
	-- store the timer id in a table, using the player as index
	colshapeTimer[player] = setTimer(outputChatBox,10000,1,"The player stayed 10 seconds in the colshape!")
end
addEventHandler("onColShapeHit",getRootElement(),colShapeHit)

function colShapeLeave(player)
	-- add a check for the element type
	if (getElementType(player) ~= "player") then return end
	-- add a debug message, with the element type
	outputDebugString("colShapeLeave "..getElementType(player))
	-- kill the timer when the player leaves the colshape
	if (isTimer(colshapeTimer[player])) then
		killTimer(colshapeTimer[player])
	end
end
addEventHandler("onColShapeLeave",getRootElement(),colShapeLeave)

Debugging Performance Issues

If your server is using up more resources than it should or you just want to make sure your scripts are efficient you can find the cause using a great tool that comes with MTA SA server, performancebrowser. Make sure that its started with "start performancebrowser" if it doesn't exist then get it from the default resources that come with the server. This tool provides an incredible amount of information for performance debugging. Memory leaks, element leaks and CPU intensive scripts are all easily findable via performancebrowser. If you use -d option in Lua timing you can see which functions are using up the CPU.

To access performancebrowser you will need to go to your web browser and enter the address: http://serverIPHere:serverHTTPPortHere/performancebrowser/ Note that the / at the end is required. So for example: http://127.0.0.1:22005/performancebrowser/ You will then need to login with an in-game admin account or any account that has access to "general.HTTP" Most of the information you will need are in the categories Lua timing and Lua memory, look for values that are much higher than other values.

Examples of scripts that could cause performance problems

Adding data to a table but never removing it. This would take months/years before it causes a problem though.

local someData = {}

function storeData()
    someData[source] = true
    -- There is no handling for when a player quits, this is considered a memory leak
    -- Using the Lua timing tab you can detect the RAM usage of each resource.
end
addEventHandler("onPlayerJoin", root, storeData)

Element leaking is possible if you use temporary colshapes for whatever reason and may not destroy them. This would cause bandwidth, CPU and memory performance issues over time.

function useTemporaryCol()
    local col = createColCircle(some code here)
    if (normally this should happen) then
        destroyElement(col)
    end
    -- But sometimes it didn't so the script ended but the collision area remained and over time
    -- you may end up with hundreds to thousands of pointless collision areas. 
    -- The Lua timing tab allows you to see the amount of elements each script has created.
end

High CPU usage resulting in the server FPS dropping so much that the server is unplayable. In under 24 hours this can create havoc on a very busy server. The amount of "refs" in the Lua timing detect this type of build up, surprisingly the Lua timing tab didn't help in this case but Lua memory did.

addEventHandler("onPlayerJoin", root, function()
    -- Code for joiner
    addEventHandler("onPlayerQuit", root, function()
        -- Code for when they have quit
        -- See the problem? It's bound to root which the event handler is being added again and again and again
    end)
end)

A function uses up a lot of your CPU because whatever it does takes a long time. This is just some function that takes a long time to complete. Without performancebrowser you'd have no idea its the cause but with performancebrowser you can see that a resource is using lots of CPU in the Lua timing tab. If you then enter: -d into the options edit box it will even tell you what file name and first line of the function that is using up so much CPU.

function someDodgyCode()
    for i=1, 100000 do
        -- some code
    end
end