# Repeats

In many cases, there is a need to periodically execute some code. 
While you can create and manage threads to achieve the same effect, there are already functions to factilitate just that:

**MapGameTimeRepeat(*name*, *interval*, *func*)**
:	Declares a repeating function *func* which will be called every *interval* milliseconds of *GameTime* while there is a map loaded.

**MapRealTimeRepeat(*name*, *interval*, *func*)**
:	Declares a repeating function *func* which will be called every *interval* milliseconds of *RealTime* while there is a map loaded.

The function *func* receives as parameter the time from the previous invocation. On the first invocation it receives *nil* as parameter. 

*func* can return a value which will be used (one time only) as sleep time before the next invocation instead of the *interval* provided. 

!!! WARNING
    If *interval* is zero or a negative number *func* will be called in a loop without any delay. In that case it **must** sleep otherwise it will freeze the entire game.


Since *func* runs in its own thread it can sleep or wait for wakeup or wait for messages. You can easily wakeup a repeat function:

**WakeupPeriodicRepeatThread(*name*, ...)**
:	Wakes up the thread of the periodic repeat with *name*. To have an effect, the repeat function *func* should have called *WaitWakeup()*.

Repeats have several advantages:
- after lua reload, the new *func* is called instead of the old one
- after loading a savegame created with an old repeat func the new func gets called instead
- when loading a savegame created before the repeat was introduced in the code, the repeat is started
- the repeat is started on entering a map and stopped it when exiting the map


# Examples

Update the daily quest once a day. In this case, we know the map starts at 6am, 
so we use the first invocation when *interval* is *nil* to sleep 6 more hours 
and then call *UpdateDailyQuest()* exactly at 12h every day thereafter.

~~~~~~~~~~ Lua
MapRealTimeRepeat("", const.HourDuration * 24, function (interval)
	if not interval then
		return const.HourDuration * 6 -- sleep 6h on the first invocation
	end
	UpdateDailyQuest()
end)
~~~~~~~~~~


If updating the UI is slow, it can be done in a thread after *UpdateUI* is called 
but no more often than once every 100ms:

~~~~~~~~~~ Lua
MapVar("UIUpdatePending", false)
MapRealTimeRepeat("UpdateUI", 100, function (interval)
	if not UIUpdatePending then WaitWakeup() end
	UIUpdatePending = false
	UpdateUIForReal()
end)

function UpdateUI()
	UIUpdatePending = true
	WakeupPeriodicRepeatThread("UpdateUI")
end
~~~~~~~~~~


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