how it works?

Grand Central Dispatch (GCD) is a powerful tool in Swift for managing concurrent tasks and improving the performance of your applications. It is a low-level API for managing queues of tasks that are executed on a pool of threads, and it is designed to make it easier for developers to write efficient and responsive applications.

GCD is based on the concept of dispatching tasks to queues, which can be either serial or concurrent. A serial queue executes tasks one at a time, in the order that they are added to the queue. A concurrent queue, on the other hand, can execute multiple tasks concurrently, but the order in which they are completed is not guaranteed.

One of the main advantages of GCD is that it takes care of the details of creating and managing threads, allowing developers to focus on the tasks that need to be executed. This makes it easier to write concurrent code and helps to avoid common pitfalls such as deadlocks and race conditions.

To use GCD in Swift, you can create a dispatch queue using the DispatchQueue class. You can specify whether the queue is serial or concurrent, and you can also specify a label for the queue to help you identify it. For example:

let queue = DispatchQueue(label: "com.example.myqueue", qos: .utility, attributes: .concurrent)

To add a task to a queue, you can use the async function, which takes a closure as an argument and executes it asynchronously on the queue. For example:

queue.async {
// Perform some task
}

You can also use the sync function to execute a task synchronously on the queue. This is useful if you need to ensure that a task is completed before proceeding with the rest of your code.

GCD also provides support for group tasks, which allow you to specify a set of tasks that should be executed together. You can use the DispatchGroup class to create a group of tasks, and then use the enter and leave functions to add and remove tasks from the group. When all tasks in the group have completed, you can use the notify function to execute a closure that is called when the group is finished.

In summary, Grand Central Dispatch is a powerful tool for managing concurrent tasks in Swift. It provides a simple and efficient way to perform tasks asynchronously and improve the performance of your applications. By using GCD, you can write responsive and performant code, without having to worry about the details of thread management.