Apparently random execution time with GKGraph.findpath() method in Swift - swift

Question

I'm having a pathfinder class in a SpriteKit game that a I want to use to process every path request in the game. So I have my class stored in my SKScene and I access it from different parts of the game always from the main thread. The pathfinder uses a GKGridGraph of a pretty good size (288 x 224). The class holds an array of requests processed one after another at each update() call from the main scene. Here is the code :
class PathFinder {
var isLookingForPath = false
var groundGraph : GKGridGraph<MyNode>?
var queued : [PathFinderRequest] = []
var thread: DispatchQoS.QoSClass = .userInitiated
func generate(minPoint: CGPoint) {
// generate the groundGraph grid
}
func update() {
// called every frame
if !self.isLookingForPath {
findPath()
}
}
func findPath(from start: TuplePosition, to end: TuplePosition, on layer: PathFinderLayer, callBack: PathFinderCallback) {
// Generating request
let id = String.randomString(length: 5)
let request = PathFinderRequest(id: id, start: start, end: end, layer: layer, callback: callBack)
// Append the request object at the end of the array
queued.append(request)
}
func findPath() {
self.isLookingForPath = true
guard let request = queued.first else {
isLookingForPath = false
return
}
let layer = request.layer
let callback = request.callback
let start = request.start
let end = request.end
let id = request.id
var graph = self.groundGraph
queued.removeFirst()
let findItem = DispatchWorkItem {
if let g = graph, let sn = g.node(atGridPosition: start.toVec()), let en = g.node(atGridPosition: end.toVec()) {
if let path = g.findPath(from: sn, to: en) as? [GKGridGraphNode], path.count > 0 {
// Here we have the path found
// it worked !
}
}
// Once the findPath() method execution is over,
// we reset the "flag" so we can call it once again from
// the update() method
self.isLookingForPath = false
}
// Execute the findPath() method in the chosen thread
// asynchronously
DispatchQueue.global(qos: thread).async(execute: findItem)
}
func drawPath(_ path: [GKGridGraphNode]) {
// draw the path on the scene
}
}
Well the code works quite good as it is. If I send random path request within (x+-10, y+-10) length it will return them to each object holding the callback in the request object pretty quickly, but suddenly one request is randomly taking a huge amount of time (approximatively 20s compared to 0.001s) and despite everything I tried I wasn't able to find out what happens. It's never on the same path, never the same caller, never after a certain amount of time... here is a video of the issue : https://www.youtube.com/watch?v=-IYlLOQgJrQ
It sure happens more quickly when there is too much entities requesting but I can't figure why I'm sure it has to deal with the DispacthQueue async calls that I use to prevent the game from freezing.
With delay on every call, the error appear later but is still here :
DispatchQueue.global(qos: thread).asyncAfter(deadline: .now() + 0.1, execute: findItem)
When I look for what is taking so much time to process it is a sub method of the GKGridGraph class :
So I really don't know how to figure this out, I tried everything I could think of but it always happens whatever the delay, the number of entities, the different threads, etc...
Thank you for your precious help !