What difficulties can a system face when working with multithreading?

When working with multithreading in iOS systems, the following difficulties may arise:

• Race conditions: when multiple threads simultaneously access and modify shared data, leading to unpredictable results.
• Deadlocks: a situation where two or more threads wait for each other, causing the program to halt.
• Synchronization issues: the need to properly use synchronization mechanisms (e.g., DispatchQueue, NSLock, semaphore) to avoid conflicts.
• Thread lifecycle management: creating too many threads can lead to decreased performance.
• Updating UI from background threads: in iOS, updating the user interface should only occur on the main thread, otherwise crashes or incorrect display may occur.

Example of using GCD for safe UI updates:

DispatchQueue.global(qos: .background).async {
    // Perform heavy task in background thread
    let data = fetchData()
    DispatchQueue.main.async {
        // Update UI on main thread
        self.label.text = data
    }
}