Seeking definitive clarification on the memory management behavior and thread safety issue when an instance method of a class marked with or confined to the @MainActor is called implicitly within a Task closure defined inside another @MainActor method.
Specifically, we observe that static analysis tools like SwiftLint's (explicit_self rule or Use weak self in closures Violation: Use weak self when create a closure.(weak_self_closure) often flag the use of self. inside the Task block as a potential, unhandled strong reference cycle, requiring the use of [weak self].
My understanding is that a strong reference cycle requires A (the class instance) to hold a strong reference to B (the closure/task) and B to hold a strong reference back to A (self). Since the Task is an ephemeral block of asynchronous work not captured or stored as a property of self, we do not believe a classic retain cycle exists, provided the Task naturally completes.
Need confirmation on whether the Swift Concurrency runtime creates any internal strong reference that could cause a memory leak if self is captured strongly here and clarify Any thread safety issue occurs ( not a retain cycle).
Retain Cycle Guarantee: Can you confirm that the strong capture of self within the Task { ... } closure does not create a strong reference cycle (i.e., a memory leak where deinit is never called) because the Task is not stored as a property?
Best Practice vs. Necessity: If a retain cycle is guaranteed not to occur, is using [weak self] purely an optional best practice to allow the Task instance to be deallocated before the asynchronous work completes, or is it necessary to prevent a genuine memory leak?
Threading Safety: Since Task is implicitly isolated to the @MainActor, and the Task block is started within an @MainActor function, are there any threading concerns regarding the implicit capture of self before the first await point, or does the runtime handle the isolation guarantee completely regardless of the capture list?
STEPS TO REPRODUCE
Here is the code snippet:
Does using self inside a fire-and-forget Task { MainActor in} closure (Not stored as a property) create a retain cycle / crash issue or any thread safety related issue ?
class MyOtherViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
doSomething()
}
func doSomething() {
// Fire and forget , Task not stored as a property
Task { @MainActor in
self.updateUI()
}
}
func updateUI() {
// Example UI Update
self.view.backgroundColor = .systemGreen
print("UI updated!")
}
}
If [weak self] is already captured in an outer closure, is it necessary to capture [weak self] again in nested closures ?
class MyViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
startProcess()
}
func startProcess() {
perfromStepOne { [weak self] in
guard let self = self else { return }
self.performStepTwo {
self.doSomething() // is this safe ?
}
}
}
func performStepOne(completion: @escaping () -> Void) {
// Simulate a step, then call completion
print("step one complete")
completion()
}
func performStepTwo(completion: @escaping () -> Void) {
// Simulate a step, then call completion
print("step two complete")
completion()
}
func doSomething() {
print("Do Something")
}
}