Grand Central Dispatch Tutorial for Swift 5: Part 1 2 Kodeco, the new raywenderlich com

Touch device users, explore by touch or with swipe gestures. In Part 2 of this tutorial, you’ll dive even deeper into GCD’s API to do even more cool stuff. Our iOS Concurrency with GCD and Operations video course also covers a lot of the same 11 Best Freelance Game Developers Hire in 48 Hours topics covered in this tutorial. One that you may have noticed when running it is that the download complete alert is premature. Get an in depth look at what’s covered in our video tutorial course iOS Concurrency with GCD & Operations.

Congratulations — your PhotoManager singleton is now thread-safe! No matter where or how you read or write photos, you can be confident that it will happen in a safe manner with no surprises. It should behave as before, but underneath the hood, you have some happy threads. Two or more items — in most cases, threads — deadlock if they get stuck waiting for each other to complete or perform another action. The first can’t finish because it’s waiting for the second to finish, but the second can’t finish because it’s waiting for the first to finish. Use sync to keep track of your work with dispatch barriers or when you need to wait for the operation to finish before you can use the data processed by the closure.

swift 3 gcd

You submit units of work to this queue, and GCD executes them in a FIFO order , guaranteeing that the first task submitted is the first one started. GooglyPuff is a non-optimized, “thread-unsafe” app that overlays googly eyes on detected faces using Core Image’s face detection API. You can select images on which to apply this effect from your photo library or download images from the internet. To execute a task, this has to be dispatched to an appropriate dispatch queue. Tasks can dispatched synchronously or asynchronously, singly or in groups.

A quick look at Grand Central Dispatch and Swift 3

The choice of approach depends on other aspects of what you’re writing – there’s much to consider with threading. While these algorithms all calculate the same result, comparing their plane complexity might not be enough to decide for one of them, though. The original iterative Euklidean algorithm is easier to understand. The Grand Central Dispatch was first introduced in iOS 4 and was written in C programming language. The GCD coding style was quite close to low level C syntax and had none of the Swift language design features.

It may look like there’s a lot of copying in your code when passing collections back and forth. The Swift collection types are optimized to make copies only when necessary, for instance, when your app modifies an array passed by value for the first time. To use Timer, you have to define a method, then create the timer with a selector or invocation to the defined method. With DispatchQueue and asyncAfter(), you simply add a closure. Head back to the app and add some photos from your photo library or use the Le Internet option to download a few.

This tutorial will help you to better understand how GCD works with serial and concurrent queues. It’s also beneficial to learn about these new asynchronous features that are now available. Grand Central Dispatch is a low-level API for managing concurrent operations. It can help improve your app’s responsiveness by deferring computationally expensive tasks to the background. It’s an easier concurrency model to work with than locks and threads. Learn the basics of concurrency and Grand Central Dispatch — serial and concurrent queues, synchronous and asynchronous dispatch.

swift 3 gcd

Tasks starts in the order in which they are added in the queue, but their execution occur concurrently and they don’t have to wait for each other to start. GCD provides dispatch queues to manage tasks that can be executed in a FIFO pattern guaranteeing that the queue that comes first for execution will also finish first. Finally, you post a notification that you’ve added the photo. You must post this notification on the main thread because it will do UI work.


It offer great flexibility and options when trying to achieve concurrency, performance, and parallel tasks. Apple/swift-evolution swift-evolution – This maintains proposals for changes and user-visible enhancements to the Swift Programming Language. If you want to try the other QoS queues, you could also use .userInteractive, .utility or .background.

  • DispatchQueue() , DispatchGroup(), DispatchWorkItem(), DispatchSource() to name just a few.
  • You move the work to a background global queue and run the work in the closure asynchronously.
  • In general, you want to use async when you need to perform a network-based or CPU-intensive task in the background without blocking the current thread.
  • This will indicate the task’s importance and guide GCD into determining the priority to give to the task.
  • GCD creates for you a number of queues, and places tasks in those queues depending on how important you say they are.
  • Dispatch queues are thread-safe which means that we can access them from multiple threads simultaneously.

Notice how in normal operation, the queue acts just like a normal concurrent queue. But when the barrier is executing, it essentially acts as a serial queue. After the barrier finishes, the queue goes back to being a normal concurrent queue.

Method 2 – Recursive Method

GCD provides an elegant solution of creating a read/write lock using dispatch barriers. Dispatch barriers are a group of functions acting as a serial-style Create cool applications that integrate with WordPress com bottleneck when working with concurrent queues. As the name suggests, concurrent queues allows us to execute multiple tasks in parallel.

Note that because our code is now inside a closure, we need to prefix our method calls with self. Step 4 − Call the function and store the result in “result” variable. Step 2 − Declare a int type variable named res to store the reminder. This tutorial will discuss how to write a Swift program to find GCD of two numbers. ShowOrHideNavPrompt() executes in viewDidLoad() and any time your UICollectionView reloads.

swift 3 gcd

Anyway there may still be times when we need to add a task synchronously to prevent race conditions or other synchronization issues. When we choose to create a queue as serial queue, the queue can only execute one task at a time. All tasks in the same serial queue will respect each other and execute serially.

So you dispatch another task asynchronously to the main queue to trigger the notification. Thread-safe code can safely be called from multiple threads or concurrent tasks without causing any problems such as data corruption or app crashes. Code that isn’t thread-safe can only run in one context at a time. Concurrent tasks on the other hand are managed and controlled by developers , we can dispatch multiple block of codes through multiple concurrent tasks. You still have to deal with thread safety when accessing code in the singleton that manipulates shared internal data. Handle this through methods such as synchronizing data access.

GCD differences in Swift 3

I have read elsewhere that this only occurs if no “save” of the object model was made before creating the managed objects. Also in the Data Model Inspector there is a new “Codegen” selection box. By default it is set to “Manual/None” which is the same behaviour as before.

iOS Concurrency with GCD and Operations

Most classes, like the first three just mentioned start in activated state, which means they are ready to use right away. Others like DispatchSource() have to be set active first to be useful. Secondly, DipatchObjects can be suspended or resumed if needbe via suspend() or resume(). But mind when The Continuous Delivery Maturity Model dealing with DispatchQueues that a queue excutes all its operations first before transitioning to its suspended state. The async() method takes one parameter, which is a closure to execute asynchronously. We’re using trailing closure syntax, which removes an unneeded set of parentheses.

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