Can you explain what is meant by the term Lock in the context of multithreading or synchronization?

Lock — a synchronization mechanism used to control access to shared resources in a multithreaded environment. It ensures that only one thread can execute a critical section of code at a time, preventing race conditions and maintaining data integrity.

In iOS, objects like NSLock, DispatchSemaphore, or @synchronized are often used for this purpose.

Example of using NSLock:

let lock = NSLock()

func criticalSection() {
    lock.lock()
    // code that should only be executed by one thread
    lock.unlock()
}

Without locking, multiple threads could modify data simultaneously, leading to errors.