On Apr 20, 2010, at 10:36 AM, Bill wrote: >> And what make NSCache and NSDiscardableContent not appropriate here ? > > They are not inappropriate, but they require a lot more work than a simple > warning sent via a notification or other means.
The iPhone has a much simpler memory model than Mac OS (or Windows or Linux). It doesn’t have virtual memory, and it also has very limited RAM. This makes low-memory warnings necessary. With virtual memory, things are more complicated. The good news is that on Mac OS your process won’t “run out of memory” until it allocates about 3GB of heap if it’s 32 bit; if it’s 64-bit it will never run out of memory*. The bad news is that before that happens, the VM paging is likely to slow your machine to a crawl, as everything else on the system gets paged out. So the danger on Mac OS X is not running out of memory, it’s using too much RAM and swap space, causing performance to suffer. Avoiding this is tricky because it depends on the differences between address space, RAM and backing store. You can allocate a gigabyte of address space with no ill effects as long as you don’t map any of it in. But conversely, merely accessing a large already-malloced block might cause your process to block for hundreds of milliseconds if that address space was paged out. NSCache and NSDiscardableContent are high-level constructs that try to simplify these decisions and make them easier to use. Yes, they’re more complex than a simple “please free up memory right now” warning. But they make a lot more sense on Mac OS. (And in practice, they end up automating what you’d probably already be doing in response to a low-memory warning, i.e. looking for data that can be safely thrown away and freeing it.) —Jens * It will, however, eventually fill up your hard disk with VM backing store files. When this happens the OS starts suspending processes while it puts up a critical alert asking you to quit apps or free up disk space._______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
