How is asynchronous task processing implemented in a sequential queue?

In iOS, asynchronous task processing in a serial queue is usually implemented using DispatchQueue from GCD (Grand Central Dispatch).

A serial queue guarantees that tasks will be executed one after another in order, but asynchronously, without blocking the main thread.

Example of creating and using a serial queue:

let serialQueue = DispatchQueue(label: "com.example.serialQueue")

serialQueue.async {
    // First task
    print("Task 1")
}

serialQueue.async {
    // Second task, will start after the first completes
    print("Task 2")
}

Here, async places tasks in the queue and immediately returns control, while tasks are executed sequentially in the order they were added. This is convenient for synchronizing access to resources or for step-by-step data processing without blocking the UI.