What are the main mechanisms for thread synchronization that you know?

In iOS, several main mechanisms are used for thread synchronization (parallel code execution):

• GCD (Grand Central Dispatch) — a high-level API for managing task queues. It allows executing tasks asynchronously or synchronously on different queues (serial, concurrent).

• NSOperation and NSOperationQueue — an object-oriented way to manage operations, with the ability to set dependencies between them.

• Locks (NSLock, pthread_mutex) — primitives for locking to protect critical sections.

• Dispatch Semaphores — semaphores for managing access to resources.

• @synchronized — syntactic sugar for locking code in Objective-C.

Example of using GCD for synchronous execution on the main queue:

DispatchQueue.main.sync {
    // Code that should run on the main thread
}

To protect data from concurrent access, locks or serial execution of tasks on a serial queue are often used.