#Swift share array between threads software#
#Swift share array between threads code#

Such as situation has long been a problem in software engineering, with the overall issue being that shared mutable state leads to non-deterministic behavior in our software. When this data is mutable - i.e when the accessors can modify the data - there is a real possibility that the data will be changed by one accessor when another accessor is simply trying to read the data. Shared state is data that is shared across multiple accessors, which can be threads, queues, etc. It’s hard to reason about shared mutable state. In addition to these bugs, we see the beginning of a “ pyramid of doom” at line 23, caused by the use of nested closures. In lines 16 and 35, we forget to do this. Also, we can’t use Swift’s error handling capabilities here, and so we have to ensure we explicitly call the completion handler at the correct points. As our function does not return a value, Swift fails to catch the error at line 7 where we forget to call return.

What we probably anticipated to be relatively straightforward code turns out to be - in this example - a bug-filled nightmare. The code for our model types is as follows:Ī lot of code, and a large surface area for potential bugs. If this is successful, we want to wrap the initial model and related image in a new model and return this to the function’s caller. When we successfully receive this data, we want to perform a second network request, this time to fetch a related image. We want to implement a function to perform a network request to fetch some data which corresponds to one of our models. To help demonstrate this, let’s examine an implementation that exhibits the following expected behavior.

Currently, working with asynchronous APIs in Swift means using closures and completion handlers, which can lead to overly complex, error-prone implementations. Working with existing asynchronous APIs is error-prone and onerous. However, as the number of CPU cores available is finite, continually bringing up new threads will eventually lead to overcommitting the system with more threads than CPU cores, leaving the OS overwhelmed. This will continue to happen as more threads are blocked. When a thread that is being used by a GCD queue is blocked, a new thread can be brought up. You will see a few things that are unusual in this code compared to standard Swift code, but thanks to Apple’s work on interoperability with Objective-C, it works just fine.Why a New Concurrency Model? Thread ExplosionĮxisting OS abstractions for implementing concurrency, such as Grand Central Dispatch, can lead to a situation known as ‘ thread explosion’. Not a lot has changed about it between iOS 7 and iOS 9. UIActivityViewController is an Objective-C API. Today though, we are just going to cover the built in aspects of using UIActivityViewController in your Swift app. If you’ve paid any attention to WWDC a few years, you have probably saw that this is the new home for Share and Action extensions. I think I originally started with “share sheet” and went on from there, so it may seem silly to point out something so obvious, but when I first tried, I knew what I wanted, I just had no idea what it was called. When I first learned about it, I didn’t even know what to search for.

That interface is known as the UIActivityViewController. In several iOS apps, such as Safari or the Camera app, you can click a button that brings up an interface that makes it easy to send or share what you are looking at via messages, Twitter, Facebook, etc.

#Swift share array between threads software#

#Swift share array between threads code#