On 8 Oct 2014, at 13:42, Quincey Morris <quinceymor...@rivergatesoftware.com> wrote:
> (reposted after editing for length) > > On Oct 7, 2014, at 22:12 , Gerriet M. Denkmann <gerr...@mdenkmann.de> wrote: > >> Is there a way for the app to find out how much memory it is currently using? > > Here’s my take on this, which may be way off base: > > There’s really no practical way to answer such questions any more. The way > memory is managed is so varied, so diffused that even if you could get an > answer, it would be as likely to lead you astray as to help you. > > In practice, I think the question is not how much memory your app is using, > but how fast your memory use is increasing over time. > > If it’s not increasing over time It's not. Checked also with Leaks Instrument. > — then you have a fairly easy evaluation. Your app fits (in the foreground) > or it crashes. Your app retreats gracefully (to the background) or it’s > terminated. It runs in the foreground. But when in background it sometimes gets terminated. > >> When I have a file of 100 KB and do: >> myData = [NSData dataWithContentsOfFile:options:error: ]; >> myBytes = myData.bytes; >> how much Ram am I now using? 100 KB or 200 KB? I.e. does "bytes" just return >> a pointer to some internal structure in NSData? >> >> Would options = NSDataReadingMappedIfSafe be of some help? > > The general answer is that you don’t know how much it’s using. In practice, > the answer used to be 100KB (“bytes” returned an interior pointer). But this > isn’t always true any more. GCD data blocks, which can be bridged to NSData, > can come in pieces, and in that case “bytes” may copy the data into > contiguous memory. > > Mapped data might help in common cases, but how does this save you from “it > fits or it crashes” when the file turns out to be on a non-local file system, > on which mapping doesn’t work? Memory mapping is more about performance than > size, perhaps. I made a small iOS app which has just 3 buttons: Data (loads NSData from file, which resides in the app bundle) Bytes (which uses myData.bytes) Count (which sums all bytes in myData) Result with NSDataReadingMappedIfSafe, Persistent Bytes in Instruments, Allocations: No change with any button (always ca. 3.5 MB). Data button takes 1 msec, Bytes 73 μsec, first Count takes 250 msec longer than subsequent Counts. Without NSDataReadingMappedIfSafe: Data button increases Ram use by 15 MB (about size of file); takes 250 msec. Bytes, Count: no change. Bytes takes 13 μsec. All Counts take same time (ca. 50 msec). So NSDataReadingMappedIfSafe seems to be a good idea (at least in my case of a fixed file in the app bundle). > You can easily use a construct like GCD semaphores... Sounds too much work for now. Maybe to be considered later. Thanks for your ideas though. Kind regards, Gerriet. _______________________________________________ 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: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
