Why does mmap fail on iOS?

Question

I\'m trying to use mmap to read and play audio files on iOS. It works fine for files up to about 400MB. But when I try a 500MB file, I get a ENOMEM error.

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Answer 1

After further investigation and reading this excellent blog post by John Carmack, here are my conclusions:

• 700MB is the limit for virtual memory on iOS (as of 2012, 32-bit iOS)
• It may or may not be available in a single block; this depends on device state and app behaviour

Therefore, to reliably mmap 700MB worth of file data it is necessary to break it into smaller chunks.