NSUserDefaults+SimulatorPerformance

Purpose

In iOS 8, NSUserDefaults read performance in the simulator declined significantly. For apps that read from NSUserDefaults often, this causes sluggishness while debugging and a misleading discrepancy between the real device and the simulator.

This project includes an NSUserDefaults category named NSUserDefaults+SimulatorPerformance that dramatically improves read performance in the simulator by adding a man-in-the-middle write-through cache in memory. It does so by swizzling out all of NSUserDefaults' setters and getters and replacing them with fl_-prefixed methods that correctly populate and update a cache.

Demo Project

A demo project is provided to illustrate the performance improvements this project has.

It includes three commands:

• Write will write a set of entries into NSUserDefaults. The count of entries written is determined by the slider below.
• Read (Slow) will read a set of entries from NSUserDefaults using the default uncached implementation of -setObject:forKey:. The count of entries read is determined by the slider below.
• Read (Fast) will read a set of entries from NSUserDefaults using the swizzled, cached implementation of -setObject:forKey:. The count of entries read is determined by the slider below.

Note that the first time Read (Fast) is tapped it will likely have performance similar to Read (Slow) because the cached values for the entries being read aren't updated yet. On subsequent uses of the Read (Fast) button you should see significant performance gains.

Installation

Using this project is easy! All you have to do to start using it is include the NSUserDefaults+Simulator .h/.m pair in your project, that's it. This category automatically swizzles out NSUserDefaults' methods when the class is loaded if TARGET_IPHONE_SIMULATOR is on. If this is loaded, you'll see the following log at launch time.

Extensions

Important Note:

Because use of NSUserDefaults+SimulatorPerformance adds a level of indirection between you and the actual values stored in NSUserDefaults, it may cause issues when debugging extensions.

Writes from an app to an instance of NSUserDefaults that's shared with an extension will go through synchronously since the write methods in this category are write-through.

However, values written by an extension to an instance of NSUserDefaults shared with an app may be inconsistent when read by that app if a cached value exists. This is because writes to NSUserDefaults in other processes will not update the in-memory cache this category uses.

It is highly recommended that if you're going to be testing an extension that you disable this category.

License

This project is available under the BSD 3-clause license. See the LICENSE file for more info.