Identifying memory leak in Swift GCD.async call - swift

Question

Some background about my app: I am drawing a map. When the user moves the map I perform a database query. I first do an rTree query to find the features that would be draw in the current viewport. Once I have those IDs I perform a second database query to extract the features (geojson) from the database. I do a quick check to see if the item already has been drawn, if not I do a addChild to render the feature on the map. I want to do these database looks up in the background via GCD so the user can move the map smoothly. I've implemented this but the memory usage quickly grows to 1gb, whereas if I do all the work in the main thread it uses around 250mb (acceptable for me). I'm assuming something is not being cleaned up because of the closure use. Any insight into the cause of the memory leak is appreciated.
public func drawItemsInBox(boundingBox: [Double]) {
DispatchQueue.global(qos: .background).async { [weak self] in
guard let self = self else {
return
}
var drawItems: [Int64] = []
let table = Table("LNDARE_XS")
let tableRTree = Table("LNDARE_XS_virtual")
let coords = Expression<String?>("coords")
let foid = Expression<String>("foid")
let rTree = Expression<Int64>("rTree")
let minX = Expression<Double>("minX")
let maxX = Expression<Double>("maxX")
let minY = Expression<Double>("minY")
let maxY = Expression<Double>("maxY")
let id = Expression<Int64>("id")
// find all the features to draw via an rTree query
for row in try! self.db.prepare(tableRTree.filter(maxX >= boundingBox[0] && minX <= boundingBox[1] && maxY >= boundingBox[2] && minY <= boundingBox[3])) {
drawItems.append(row[id])
}
do {
// get all the features geojson data
let query = table.filter(drawItems.contains(rTree))
for row in try self.db.prepare(query) {
// skip drawing if the feature already exists on the map
if self.featureTracking["LNDARE_XS"]?[Int64(row[foid])!] == nil {
// convert the database string to an array of coords
var toBeRendered:[CGPoint] = []
let coordsArray = row[coords]!.components(separatedBy: ",")
for i in 0...(coordsArray.count / 2) - 1 {
toBeRendered.append(CGPoint(x: (Double(coordsArray[i*2])!), y: (Double(coordsArray[(i*2)+1])!)))
}
let linearShapeNode = SKShapeNode(points: &toBeRendered, count: toBeRendered.count)
linearShapeNode.position = CGPoint(x: self.frame.midX, y: self.frame.midY)
linearShapeNode.lineWidth = 0
linearShapeNode.fillColor = NSColor.black
// append the featureId for tracking and call addChild to draw
self.scaleLayer.addChild(linearShapeNode)
self.featureTracking["LNDARE_XS"]?[Int64(row[foid])!] = linearShapeNode
}
}
} catch {
// catch
}
}
}

Answer 1

Maybe change toBeRendered can save some:
var toBeRendered:[CGPoint] = []
for row in try self.db.prepare(query) {
// skip drawing if the feature already exists on the map
if self.featureTracking["LNDARE_XS"]?[Int64(row[foid])!] == nil {
// convert the database string to an array of coords
toBeRendered.removeAll()
let coordsArray = row[coords]!.components(separatedBy: ",")
for i in 0...(coordsArray.count / 2) - 1 {
toBeRendered.append(CGPoint(x: (Double(coordsArray[i*2])!), y: (Double(coordsArray[(i*2)+1])!)))
}

Answer 2

Maybe try using an auto release pool since you are not on the main thread
public func drawItemsInBox(boundingBox: [Double]) {
DispatchQueue.global(qos: .background).async { [weak self] in
guard let self = self else {
return
}
var drawItems: [Int64] = []
let table = Table("LNDARE_XS")
let tableRTree = Table("LNDARE_XS_virtual")
let coords = Expression<String?>("coords")
let foid = Expression<String>("foid")
let rTree = Expression<Int64>("rTree")
let minX = Expression<Double>("minX")
let maxX = Expression<Double>("maxX")
let minY = Expression<Double>("minY")
let maxY = Expression<Double>("maxY")
let id = Expression<Int64>("id")
// find all the features to draw via an rTree query
for row in try! self.db.prepare(tableRTree.filter(maxX >= boundingBox[0] && minX <= boundingBox[1] && maxY >= boundingBox[2] && minY <= boundingBox[3])) {
drawItems.append(row[id])
}
do {
// get all the features geojson data
let query = table.filter(drawItems.contains(rTree))
for row in try self.db.prepare(query) {
autoreleasepool{
// skip drawing if the feature already exists on the map
if self.featureTracking["LNDARE_XS"]?[Int64(row[foid])!] == nil {
// convert the database string to an array of coords
var toBeRendered:[CGPoint] = []
let coordsArray = row[coords]!.components(separatedBy: ",")
for i in 0...(coordsArray.count / 2) - 1 {
toBeRendered.append(CGPoint(x: (Double(coordsArray[i*2])!), y: (Double(coordsArray[(i*2)+1])!)))
}
let linearShapeNode = SKShapeNode(points: &toBeRendered, count: toBeRendered.count)
linearShapeNode.position = CGPoint(x: self.frame.midX, y: self.frame.midY)
linearShapeNode.lineWidth = 0
linearShapeNode.fillColor = NSColor.black
// append the featureId for tracking and call addChild to draw
self.scaleLayer.addChild(linearShapeNode)
self.featureTracking["LNDARE_XS"]?[Int64(row[foid])!] = linearShapeNode
}
}
}
} catch {
// catch
}
}
}