Thread: how to write a timer?

Hey all, sorry if this is the wrong forum to post it in, seemed like the closest (or at least most active) part of the Lua scripting forums for my question.

I'm writing my first plugin, and I'm still quite a newbie when it comes to programming in general (no formal training) but I've been able to nearly finish my plugin until I ran into a problem trying to write a timer. Essentially I'm trying to write a simple timer that will call a function, wait 60 seconds, and then call another function. I've tried a few ways to get this to work using Turbine.Engine.GetGameTime(), something along the lines of:

Code:

function timer(duration,startTime)
    local completed = false
    local timestamp = Turbine.Engine.GetGameTime()
    if timestamp >= startTime + duration then
        completed = true
        return completed
        else
        timer(duration,startTime)
    end
end
curTime = Turbine.Engine.GetGameTime()
if timer(60,curTime) == true then
        <do more stuff>
end

that particular one got " \Main.lua:199: stack overflow" but it was a bit of a shot in the dark to begin with

I've also tried using while loops which crashed the client (such as: while timestamp <= duration do <stuff> timestamp = Turbine.Engine.GetGameTime() else <more stuff> )

anyway, I'm wondering if there is a way to accomplish this that I'm not seeing,or maybe if there's a way to fix my nubby little code there to make it work.

Thanks in advance
-Iinferno

The simplest solution would be to use an Update event handler to compare the current game time to a desired game time. The reason you use the Update event is that it fires asynchronously, allowing you to check the time once every time a frame is rendered, preventing the endless loops you were encountering. A more robust solution is to use a Timer class which can be instantiated as many times as needed, will support the AddCallback/RemoveCallback mechanism and will thus allow triggering multiple events if needed:

Code:

function AddCallback(object, event, callback)
    if (object[event] == nil) then
        object[event] = callback;
    else
        if (type(object[event]) == "table") then
            table.insert(object[event], callback);
        else
            object[event] = {object[event], callback};
        end
    end
    return callback;
end
function RemoveCallback(object, event, callback)
    if (object[event] == callback) then
        object[event] = nil;
    else
        if (type(object[event]) == "table") then
            local size = table.getn(object[event]);
            for i = 1, size do
                if (object[event][i] == callback) then
                    table.remove(object[event], i);
                    break;
                end
            end
        end
    end
end
Timer = class( Turbine.UI.Control );
function Timer:Constructor()
    Turbine.UI.Control.Constructor( self );
    self.EndTime=Turbine.Engine.GetGameTime();
    self.Repeat=false;
    self.SetTime=function(sender, numSeconds, setRepeat)
        numSeconds=tonumber(numSeconds);
        if numSeconds==nil or numSeconds<=0 then
            numSeconds=0;
        end
        self.EndTime=Turbine.Engine.GetGameTime()+numSeconds;
        self.Repeat=false; -- default
        self.NumSeconds=numSeconds;
        if setRepeat~=nil and setRepeat~=false then
            -- any non-false value will trigger a repeat
            self.Repeat=true;
        end
        self:SetWantsUpdates(true);
    end
    self.Update=function()
        if self.EndTime~=nil and Turbine.Engine.GetGameTime()>=self.EndTime then
            self:SetWantsUpdates(false); -- turn off timer to avoid firing again while we are processing (not likely but it's a good practice)
            -- fire whatever event you are trying to trigger
            if self.TimeReached~=nil then
                if type(self.TimeReached)=="function" then
                    self.TimeReached();
                elseif type(self.TimeReached)=="table"  then
                    for k,v in pairs(self.TimeReached) do
                        if type(v)=="function" then
                            v();
                        end
                    end
                end
            end
            if self.Repeat then
                self.EndTime=Turbine.Engine.GetGameTime()+self.NumSeconds;
                self:SetWantsUpdates(true);
            end
        end
    end
end
-- somewhere else in code, you would instantiate an instance of the timer
timer1=Timer();
-- then set the TimeReached event handler
myEvent=function()
    Turbine.Shell.WriteLine("Timer Just Fired!");
end
AddCallback(timer1,"TimeReached",myEvent)
-- and finally, set the timer
timer1:SetTime(60, true); -- cause the timer to fire every 60 seconds, auto repeating

Ideally you would also call RemoveCallback(timer1,"TimeRea ched",myEvent) when your plugin unloads or the timer is no longer needed.

EDIT: Fixed bug in Repeat code

thanks alot very helpful info. Game servers are still down so I can't try it quite yet but I'm pretty sure that's exactly what I needed.

Originally Posted by dookie123

thanks alot very helpful info. Game servers are still down so I can't try it quite yet but I'm pretty sure that's exactly what I needed.

You're welcome. Note, there was a minor bug in the Repeat part of the code which I fixed after you posted so you probably should review the code you are using. The bug was that the line "if setRepeat~=nil and setRepeat~=false then" was incorrectly typed as "if setRepeat~=nil and self.Repeat~=false then" and the line "self.Repeat=setRepeat" should have been removed.

I will be adding this sample to the Writing LotRO Lua Plugins for Noobs thread as it seems to be a worthy addition.