[Trigger] Destroying Special Effect

[Neruvatar]

Hey hivers, I have this trigger that shows special effects when a coinbox is destroyed. The designated variable for such special effect is "specialeff[3]".

• Makhutha Gateway Coinbox
  • Events
    • Unit - A unit Dies
  • Conditions
    • (Unit-type of (Dying unit)) Equal to Coin Box
  • Actions
    • Player - Add (Random integer number between 9 and 17) to Player 1 (Red) Current gold
    • Special Effect - Create a special effect attached to the origin of (Attacked unit) using UI\Feedback\GoldCredit\GoldCredit.mdl
    • Set specialeff[3] = (Last created special effect)
    • Special Effect - Destroy specialeff[3]

Alright, my concern is, after destroying specialeff[3], can I reuse this specialeff[3] again for other types of special effect?

 

[Rheiko]

• Special Effect - Create a special effect attached to the origin of (Attacked unit) using UI\Feedback\GoldCredit\GoldCredit.mdl

Attacked unit is not the correct response for your trigger event. Use dying unit or killing unit.

You don't really need to store your that special effect into variable but well, it's okay.

For the question, yes, you can re-use the variable again for the other types of special effect with condition it won't get replaced by something else before it gets destroyed. In its current state, I'm not so sure because I think it's unsafe.

 

[Neruvatar]

Unsafe as in?

 

[Dr Super Good]

Alright, my concern is, after destroying specialeff[3], can I reuse this specialeff[3] again for other types of special effect?

You are not destroying the variable, you are destroying its contents. The variable can be reassigned to new special effects as much as you want, however do remember to eventually destroy them all to prevent leaks.

 

[Rheiko]

Unsafe as in?

In case you have another trigger with loop and the same variable is assigned there but during the loop, coin box dies and the event fires. It might mess up the other trigger. That's just my hypothesis because I haven't tried it in-game. That's why I think it's unsafe.

 

[Dr Super Good]

In case you have another trigger with loop and the same variable is assigned there but during the loop, coin box dies and the event fires. It might mess up the other trigger. That's just my hypothesis because I haven't tried it in-game. That's why I think it's unsafe.

Unsafe is probably the wrong word.

A race condition can occur in global variables due to one thread yielding for another thread. For example if a trigger thread uses the global variable index 3 to store a special effect and then deals enough damage to kill the box. That trigger thread will yield to run an on death trigger thread which will overwrite the contents of the variable with another effect which gets destroyed before returning control back to the original thread. The original thread might then try to destroy the effect but fail to do so as the reference to it was lost.

The correct solution is to use local variables rather than global variables. This requires using JASS directly. Local declared local handle variables must also be assigned null before function return to prevent a possible handle counter reference leak due to a JASS bug.