GCD running background thread in spritekit

Question

Created May ’21

Replies 1

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Participants 2

I have this problem when I am running a background thread that uses "self" to look for variables with specific names. The project crashes and says that I cant make any enumerations on the "NSArray" which I searched up, and found out that is a list of all the objects in the scene which can't be edited. So I made this dummy project to show my problem in a simpel way.
Here is the code:

Code Block import SpriteKit
import Foundation
class GameScene: SKScene{
override func sceneDidLoad() {
    
    
}
var boxArray = [String]()
var boxNumber = 1
func addBox(){
    
    var box = SKSpriteNode()
    box.size = CGSize(width: 100, height: 100)
    box.color = SKColor.red
    box.position = CGPoint(x: 0, y: 0)
    box.name = "box\(boxNumber)"
    self.addChild(box)
    boxArray.append(box.name!)
    boxNumber += 1
    
    
}
func moveBox(){
    
    
    for i in boxArray{
        if self.childNode(withName: "\(i)") != nil{
            var box = self.childNode(withName: "\(i)") as! SKSpriteNode
            box.position.x += 10
        }
    }
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    addBox()
}
override func update(_ currentTime: TimeInterval) {
    
    
    DispatchQueue.global(qos: .background).async {
        self.moveBox()
    }
}

Here is the crash report

2021-05-07 20:06:12.568267+0200 threading[99375:16974860] Metal GPU Frame Capture Enabled 2021-05-07 20:06:12.568677+0200 threading[99375:16974860] Metal API Validation Enabled IPHONE 2021-05-07 20:06:18.951497+0200 threading[99375:16975092] * Terminating app due to uncaught exception 'NSGenericException', reason: '* Collection <__NSArrayM: 0x283018060> was mutated while being enumerated.' * First throw call stack: (0x18d09d9d8 0x1a1406b54 0x18d09d39c 0x1bf463c90 0x1bf463480 0x1bf462ecc 0x1bf462e10 0x102fcc50c 0x102fcca08 0x102fcca4c 0x103733ce4 0x103735528 0x1037471e4 0x103747970 0x1d5743568 0x1d5746874) 2021-05-07 20:06:18.954714+0200 threading[99375:16975088] * Terminating app due to uncaught exception 'NSGenericException', reason: '* Collection <__NSArrayM: 0x283018060> was mutated while being enumerated.' * First throw call stack: (0x18d09d9d8 0x1a1406b54 0x18d09d39c 0x1bf463c90 0x1bf463480 0x1bf462ecc 0x1bf462e10 0x102fcc380 0x102fcca08 0x102fcca4c 0x103733ce4 0x103735528 0x1037471e4 0x103747970 0x1d5743568 0x1d5746874) libc++abi.dylib: terminating with uncaught exception of type NSException * Terminating app due to uncaught exception 'NSGenericException', reason: '* Collection <__NSArrayM: 0x283018060> was mutated while being enumerated.'

So the function "moveBox" is being ran in the background thread which is all fine and it works. But by making a new SKSpritenode I will have made a change in the NSArray by inserting a new element, therefor the app crashes.
How can I make a new SKSpriteNode, use the background thread and call a node from "self" all the same time without the app crashing?
I appreciate all the help i can get.

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Answer 1

Claude31 OP

May ’21

Where does it crash exactly ? In moveBox ?
I do not understand wheree you add a node here.

Looking at the crash report, I would do differently to enumerate the array:

Code Block func moveBox() {
    for i in 0..<boxArray.count {
        if var box = self.childNode(withName: "\(boxArray[i])") as? SKSpriteNode { // Need also to test it can be cast to SKSpriteNode
            box.position.x += 10
        }
    }
}

0