Fixing Memory Leaks In Auto UI Updates: A Deep Dive

Nov 25, 2025 by Alex Johnson 52 views

Memory leaks can be a nightmare for developers, especially when they occur in applications with intensive UI updates. These leaks can lead to performance degradation, application crashes, and a poor user experience. This article delves into a specific case of a memory leak encountered during intensive auto UI updates within the PostHog iOS SDK, version 3.35.0. We'll explore the steps to reproduce the issue, the root cause, and the proposed solution.

Understanding Memory Leaks

Before we dive into the specifics, let's briefly discuss what memory leaks are and why they're problematic. In simple terms, a memory leak occurs when an application allocates memory but fails to release it when it's no longer needed. Over time, these unreleased memory blocks accumulate, consuming available resources and potentially leading to application instability.

Memory leaks in applications with frequent UI updates can be particularly insidious. UI updates often involve creating and destroying objects, and if these objects aren't properly deallocated, the memory footprint can grow rapidly. This is especially true when dealing with value types like numbers, which can be boxed into Objective-C objects like NSNumber.

The Issue: NSNumber Allocation and Intensive UI Updates

The problem at hand arises in the PostHog iOS SDK, specifically version 3.35.0, when the application undergoes intensive UI updates. The user reported that while using the memory leak monitoring tools in Xcode, they observed a significant increase in memory usage, particularly related to NSNumber allocations. This issue was especially pronounced in projects with rapid UI refresh rates.

While NSNumber objects themselves are relatively small, the cumulative effect of allocating a large number of them can be substantial. In this case, the user observed memory usage climbing into the gigabytes, eventually causing the application to crash due to excessive RAM consumption. The memory usage was reported to increase geometrically, starting slowly but accelerating rapidly as the application approached its memory limit.

Steps to Reproduce

The user outlined the following steps to reproduce the issue:

Integrate the PostHog iOS SDK, version 3.35.0, into an iOS project.
Implement a UI that undergoes frequent updates, such as a real-time data display or an animated view.
Monitor the application's memory usage using Xcode's memory graph debugger or other memory analysis tools.
Observe the increasing NSNumber allocations and overall memory consumption, especially during periods of intensive UI updates.

The user noted that this issue was not as noticeable in applications with less frequent UI updates, highlighting the correlation between update frequency and memory leak severity.

Expected vs. Actual Result

The expected result, after adding the SDK, was for the application to maintain stable memory usage even during intensive UI updates. The actual result, however, was that the application's CPU usage reached 100%, and RAM usage gradually increased to its limit, eventually leading to a crash.

The Root Cause: JSON Decoding and NSNumber Boxing

The user identified a specific code snippet within the PostHog SDK as the likely source of the memory leak. This snippet is part of a JSON struct used for decoding JSON values. Let's examine the code in detail:

/// A helper type for decoding JSON values, which may be nested objects, arrays, strings, numbers, booleans, or nulls.
private struct JSON: Decodable {
    let value: Any

    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()

        if container.decodeNil() {
            value = NSNull()
        } else if let object = try? container.decode([String: JSON].self) {
            value = object.mapValues { $0.value }
        } else if let array = try? container.decode([JSON].self) {
            value = array.map(\.value)
        } else if let string = try? container.decode(String.self) {
            value = string
        } else if let bool = try? container.decode(Bool.self) {
            value = bool
        } else if let number = try? container.decode(Double.self) {
            value = NSNumber(value: number)
        } else if let number = try? container.decode(Int.self) {
            value = NSNumber(value: number)
        } else {
            throw DecodingError.dataCorruptedError(
                in: container, debugDescription: "Invalid JSON value"
            )
        }
    }
}

This JSON struct aims to handle various JSON value types, including numbers. The key issue lies in how numbers are handled: both Double and Int values are converted to NSNumber instances. This conversion, known as boxing, involves wrapping Swift value types (like Double and Int) into Objective-C objects (NSNumber).

While NSNumber provides flexibility in representing different number types, it comes with a performance overhead. Each NSNumber instance is an object allocated on the heap, requiring memory management. In scenarios with frequent JSON decoding, such as during intensive UI updates, the repeated allocation and deallocation of NSNumber objects can become a significant bottleneck and lead to memory leaks if not handled carefully.

The problem is exacerbated by the fact that the value property of the JSON struct is of type Any. This means that every time a number is decoded, a new NSNumber instance is created and stored in the value property. These NSNumber objects are then held in memory, potentially leading to a leak if they are not properly released.

The Solution: Using Double and Int Directly

The user proposed a simple yet effective solution: use Swift's native Double and Int types directly instead of boxing them into NSNumber. This avoids the overhead of Objective-C bridging and memory management associated with NSNumber.

By modifying the code to use Double and Int directly, the number of NSNumber allocations can be significantly reduced, mitigating the memory leak issue. This approach aligns with Swift's preference for value types, which are generally more efficient than reference types (like Objective-C objects) when used appropriately.

Implementing the Solution

To implement the solution, the JSON struct's init(from:) method needs to be modified. Instead of creating NSNumber instances, the decoded Double and Int values should be stored directly.

Here's how the modified code might look:

/// A helper type for decoding JSON values, which may be nested objects, arrays, strings, numbers, booleans, or nulls.
private struct JSON: Decodable {
    let value: Any

    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()

        if container.decodeNil() {
            value = NSNull()
        } else if let object = try? container.decode([String: JSON].self) {
            value = object.mapValues { $0.value }
        } else if let array = try? container.decode([JSON].self) {
            value = array.map(\.value)
        } else if let string = try? container.decode(String.self) {
            value = string
        } else if let bool = try? container.decode(Bool.self) {
            value = bool
        } else if let number = try? container.decode(Double.self) {
            value = number // Use Double directly
        } else if let number = try? container.decode(Int.self) {
            value = number // Use Int directly
        } else {
            throw DecodingError.dataCorruptedError(
                in: container, debugDescription: "Invalid JSON value"
            )
        }
    }
}

By simply changing value = NSNumber(value: number) to value = number for both Double and Int cases, the boxing process is avoided. This seemingly small change can have a significant impact on memory usage, especially in applications with frequent JSON decoding and UI updates.

Benefits of the Solution

Implementing this solution offers several benefits:

Reduced Memory Usage: By avoiding NSNumber allocations, the overall memory footprint of the application is reduced, preventing memory leaks and improving performance.
Improved Performance: Direct use of Double and Int avoids the overhead of Objective-C bridging, leading to faster JSON decoding and UI updates.
Simplified Memory Management: Swift's value types are automatically managed, reducing the risk of manual memory management errors.

Conclusion

Memory leaks can be a major headache in iOS development, especially in applications with intensive UI updates. This case study highlights how seemingly minor implementation choices, such as using NSNumber for JSON decoding, can lead to significant memory issues. By understanding the root cause and implementing a simple solution like using Swift's native number types, developers can prevent memory leaks, improve performance, and ensure a better user experience.

For more information on memory management and performance optimization in iOS development, check out Apple's documentation on memory management. This comprehensive resource provides valuable insights into best practices for managing memory in your iOS applications.