Saving Data from URLSession to disk and NSCache causes double the memory

Number:rdar://37082760 Date Originated:January 31 2018
Status:Closed Resolved:
Product:iOS SDK Product Version:iOS 11.2
Classification:Duplicate of 35563956 Reproducible:Always

When a 10MB file is downloaded using URLSession and written to disk and saved to NSCache the memory goes up by 20MB and doesn't go back down, in swift.

Steps to Reproduce:
Using Swift
Download file using URLSession using URLSession.dataTask(with: URL)
Save file data to disk
Save data using NSCache

In the Attached example project, pressing the button causes the above actions to occur.

Expected Results:
Memory usage goes up by around 10MB

Actual Results:
Memory usage goes up by around 20MB

Xcode 9.2 (9C40b)

iOS 11.2, Simulator and iPhone X


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