Retain cycle
Generated on 8/2/2024
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A retain cycle, also known as a reference cycle, occurs when two or more objects hold strong references to each other, preventing them from being deallocated. This can lead to memory leaks in your application.
In the context of Swift, retain cycles often occur with closures. By default, closures capture references strongly, which can create reference cycles. For example, if a closure captures a reference to an object that also holds a reference to the closure, neither can be deallocated.
To break these cycles, you can use weak or unowned references. Weak references do not increase the reference count and are set to nil
when the referenced object is deallocated. Unowned references also do not increase the reference count but are not set to nil
, so they should only be used when you are certain the referenced object will outlive the reference.
Here are some relevant segments from the WWDC sessions that discuss retain cycles and how to resolve them:
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Analyze heap memory:
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A Swift Tour: Explore Swift’s features and design:
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Explore Swift performance:
For a detailed explanation on how to identify and resolve retain cycles using the Xcode memory graph debugger, you can refer to the session Analyze heap memory.
Analyze heap memory
Dive into the basis for your app’s dynamic memory: the heap! Explore how to use Instruments and Xcode to measure, analyze, and fix common heap issues. We’ll also cover some techniques and best practices for diagnosing transient growth, persistent growth, and leaks in your app.
Explore Swift performance
Discover how Swift balances abstraction and performance. Learn what elements of performance to consider and how the Swift optimizer affects them. Explore the different features of Swift and how they’re implemented to further understand the tradeoffs available that can impact performance.
A Swift Tour: Explore Swift’s features and design
Learn the essential features and design philosophy of the Swift programming language. We’ll explore how to model data, handle errors, use protocols, write concurrent code, and more while building up a Swift package that has a library, an HTTP server, and a command line client. Whether you’re just beginning your Swift journey or have been with us from the start, this talk will help you get the most out of the language.