memory-leak-diagnosis

name	memory-leak-diagnosis
description	Use when investigating memory growth, retain cycles, leaks in Instruments, Task cancellation issues, or ARC problems in Swift 6 apps.

Memory Leak Diagnosis

Find and fix leaks and retain cycles using modern concurrency patterns.

Non-negotiables

ALWAYS	NEVER
Cancel long-lived Tasks	Infinite Task loops without cancellation
Prefer structured async over stored escaping closures	Strong self in stored closures without reason
Profile with Instruments / Memory Graph	“Optimize” without evidence of a leak
Prefer @Observable + async over Combine sinks	Ignore purple leak markers in Memory Graph

Decision tree

• Growth while navigating? → Memory Graph + Leaks instrument
• Closure / delegate cycle? → weak / remove stored closures / use async
• Background work outlives UI? → store Task, cancel in deinit / .onDisappear / .task lifecycle
• Shared mutable state? → actor

Core fixes

@Observable
final class SafeViewModel {
    private var workTask: Task<Void, Never>?

    func start() {
        workTask?.cancel()
        workTask = Task {
            while !Task.isCancelled {
                await doWork()
                try? await Task.sleep(for: .seconds(1))
            }
        }
    }

    func stop() {
        workTask?.cancel()
        workTask = nil
    }

    deinit { workTask?.cancel() }
}

// Prefer .task for automatic cancellation with view lifetime
.task {
    await viewModel.load()
}

Instruments quick path

1. Product → Profile → Leaks (or Allocations)
2. Exercise suspect flows
3. Inspect Cycles & Roots
4. Confirm fix with Memory Graph (no abandoned graphs)

Common leak sources

Pattern	Fix
Uncancelled Task	Cancel + check Task.isCancelled
Stored closure capturing self	weak self or async API
NotificationCenter observer	AsyncSequence notifications + cancel
Timer	invalidate / use async loop with cancel

Pre-finish checklist

• Root cause identified (not guessed)
• Cancellation/ownership fixed
• Re-profiled or Memory Graph clean for the flow