What is the purpose and use of primitives for thread synchronization in multithreaded applications?

Synchronization primitives in multithreaded applications are used to coordinate access to shared resources and prevent race conditions.

Main tasks:

• Ensure mutual exclusion (mutex) — so that only one thread can work with the critical section at a time.
• Synchronize the order of thread execution (semaphores, condition variables).
• Ensure the atomicity of operations.

In iOS (Objective-C/Swift), the following are often used:

• NSLock — a simple mutex.
• DispatchSemaphore — a semaphore to limit the number of concurrently executing threads.
• @synchronized (Objective-C) — syntactic sugar for mutex.
• DispatchQueue — for sequential execution of tasks.

Example of using NSLock:

let lock = NSLock()

func criticalSection() {
    lock.lock()
    // work with shared resource
    lock.unlock()
}

Thus, synchronization primitives help avoid errors related to parallel access and ensure the correct operation of multithreaded applications.