How to identify memory leak with slowly eating up memory - macos

Question

I wrote a small app which calls every few seconds for checking folders. I run this app for appr. one week. Now I saw that it had occupied 32 GB of my physical 8 GB RAM. So system forced me to stop it.
So it seems that very slowly the app eats up memory. I tried Instruments. With activity monitor the only slowly growing process is "DTServiceHub". Is this something I have to watch at?
For debugging I write some information with print to standard output. Is this information dropped, because app is Cocoa app or stored somewhere till termination of the app? In this case I have to remove all these print-Statements.
Some code for looping:
func startUpdating() {
running = true
timeInterval = 5
run.isEnabled = false
setTimer()
}
func setTimer() {
timer = Timer(timeInterval: timeInterval, target: self, selector: #selector(ViewController.update), userInfo: nil, repeats: false)
RunLoop.current.add(timer, forMode: RunLoopMode.commonModes)
}
func update() {
writeLOG("update -Start-", level: 0x2)
...
setTimer()
}

Answer 1

There are several problems with your code. You should not create a Timer and then add it to a run loop every time you set it, because the run loop will retain that Timer and will never release it. Even worse is when you try to do that every time you update. Just create the timer once. If you don't need it anymore you have to invalidate it to remove it from the run loop and allow its release. If you need to adjust it just set the next fire date.
Here is an example that was tested in a playground:
import Cocoa
class MyTimer
{
var fireTime = 10.0
var timer:Timer
init()
{
self.timer = Timer.scheduledTimer(timeInterval: fireTime, target: self, selector: #selector(update), userInfo: nil, repeats: true)
}
deinit
{
// it will remove the timer from the run loop and it will enable its release
timer.invalidate()
}
#objc func update()
{
print("update")
let calendar = Calendar.current
let date = Date()
if let nextFireDate = calendar.date(byAdding: .second, value: Int(fireTime), to: date)
{
print(date)
timer.fireDate = nextFireDate
}
}
}
let timer = MyTimer()
CFRunLoopRun()

Answer 2

The problem is that your app loops forever and thus never drains the auto release pool. You should never write an app like that. If you need to check something periodically, use an NSTimer. If you need to hear about changes in a folder, use NSWorkspace or kqueue or similar. In other words, use callbacks. Never just loop.