Monthly Archives: February 2012

 
17
Feb
2012
 

Extending NSData and (not) Overriding dealloc

by Tom Harrington

A couple of weeks ago Matt Long was having a problem with an app running out of memory. He had a ginormous data file he needed to load up and process, and that memory hit was more than the app could bear. It would load just fine, into an NSData, but before he could finish with it the app would run short of memory and die.

Until recently the obvious thing would have been to tell NSData to create a memory-mapped instance. Given NSString *path pointing to a file, you could create an NSData with almost no memory hit regardless of file size by creating it as:

Starting with iOS 5 though, this method has been deprecated. Instead, what you’re supposed to do is:

So, fine, whatever, it’s a different call, so what? Well, it wasn’t working. Instruments was showing that the app was taking the full memory hit when the NSData was created. Mapping wasn’t working despite using NSDataReadingMappedAlways. So what could he do? The wheels of my mind started turning.

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