How is multithreading implemented and managed in the iOS operating system?

In iOS, multithreading is implemented and managed using several key technologies:

• Grand Central Dispatch (GCD) — a high-level API for managing task queues. GCD allows creating asynchronous and synchronous tasks that run on a thread pool, automatically managing the number of threads and their scheduling.

• NSOperation and NSOperationQueue — a more object-oriented layer over GCD, enabling the creation of operations with dependencies and priorities.

• Threads (NSThread) — a lower-level way of creating and managing threads, but used less frequently due to its complexity.

iOS itself manages a thread pool, optimizing their number based on load and device resources. Developers usually work with GCD or NSOperationQueue without managing threads directly.

Example of using GCD:

DispatchQueue.global(qos: .background).async {
    // Background task
    print("Running in background thread")
    DispatchQueue.main.async {
        // UI update on the main thread
        print("Updating UI")
    }
}