How can “memory cleaner” apps determine the amount of used memory on iOS?

Question

Every now and then "memory cleaner" apps bubble to the top of the download charts on the iOS AppStore, yet I am always puzzled: How can these apps figure out how much memory is used when they are sandboxed and can't access any memory outside of their process? I'm not an expert in memory allocation on C, so maybe the solution is obvious and I just don't know it but I am curious as to how this works/could work.

Obviously the second question is how do they clean the memory once they have the count, I assume they just allocate a ton of heavy objects (eg. images) and thus force the OS to shut down other processes. Yet maybe there is a smarter way?

Note, I am not talking about Cydia here, these apps are available on the regular AppStore and work on non-cracked devices with the official consent from Apple. As an example, here is the current top seller: http://iputzfrau.professional-apps.at/

Answer 1

These apps, as with the "track any cell phone" apps that have "for entertainment purposes only" buried in line 30,239 of the description, are scams. It's exceedingly frustrating that Apple lets them through the review process.

Answer 2

The Mach/BSD host_statistics and sysctl functions are available on iOS, and they provide access to system statistics such as the amount of physical RAM, processor speed and, indeed, the amount of free RAM available. To get the latter, you'll want to call host_statistics with HOST_VM_INFO , and look at free_count in the structure it fills out for you. Note that this value isn't necessarily useful for any real purpose. You probably don't need it unless you want to write yet another one of these scammy apps.

Low-level functions in the C/UNIX/Mach/BSD layer are generally available for use in iOS apps, although these APIs typically aren't described in the SDK documentation. Look at the headers in /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.0.sdk/usr/include/ and refer to the Mac OS man pages, C/UNIX standard documents or the Mac SDKs for more details about them.

Answer 3

You're right -- there's no public API that would enable an app like the one you linked to do what it claims to do.

This would be an excellent question to pose to Apple, or at least post in the Apple developer forums. You could also report a bug , probably the most effective way to register a complaint without knocking yourself out.