Concurrency and Threading on Mobile Platforms Questions
Comprehensive understanding of concurrent programming specific to mobile. iOS: Grand Central Dispatch (GCD), OperationQueue, NSOperationQueue, thread safety, synchronization primitives. Android: ThreadPoolExecutor, Handler, HandlerThread, Coroutines, thread safety. Cross-platform reactive patterns with RxSwift, RxKotlin. Understanding race conditions, deadlocks, priority inversion, and how to design thread-safe mobile code. Real experience debugging concurrency bugs.
HardTechnical
37 practiced
You observed a priority inversion on iOS where a low-QoS task holds a lock while doing synchronous disk writes, blocking a UI task. Propose code-level fixes (for example moving disk IO out of critical sections, using atomic file writes) and larger architectural changes to eliminate the inversion. Explain how you would test under stress and which Instruments views you would use to validate the fix.
MediumTechnical
29 practiced
Compare the trade-offs of using a serial DispatchQueue, NSLock, and the Swift actor model to protect shared mutable state. For each approach describe performance characteristics, fairness, deadlock risk, composability, and Objective-C interoperability considerations and give an example scenario where it would be the preferred solution.
EasyTechnical
30 practiced
Define thread safety and provide three practical guidelines you use to ensure thread safety in mobile apps across iOS and Android, including examples such as using immutable models, thread confinement, and synchronization primitives, plus when to prefer each approach.
HardTechnical
29 practiced
Implement a lock-free concurrent FIFO queue in Java or Kotlin suitable for use on Android. Provide code or detailed pseudocode for enqueue and dequeue using AtomicReference and CAS, explain the ABA problem and one mitigation (for example version-tagging or AtomicStampedReference), and describe scenarios where this lock-free queue is preferable to synchronized collections.
MediumTechnical
41 practiced
Using Kotlin coroutines, design a cancellable API wrapper that performs a network call with automatic retries and exponential backoff. Provide sample code that runs on Dispatchers.IO, supports immediate cancellation by the caller, includes jitter on backoff, and demonstrates how to launch and cancel from a ViewModel when the view is destroyed.
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