I've written an iOS app that, according to Instruments, seems to very slowly
allocate more and more memory over time, although I can see no reason for it.
After starting it, and letting it settle down, I see in the Allocations tool
several entries in the "#Persistent" column creeping upwards. Typically, I see
an item "CFArray (mutable-variable)" incrementing its #Persistent once a
second, and an item "Malloc 32 Bytes" incrementing by 2 every second. The
Leaks tool shows nothing. Taking Generation snapshots at intervals of a second
or two shows the steady accumulation of small allocations, described as
<non-object>.
I'm using XCode 6.4 and running this in the simulator for iPhone 6 and iOS 8.4.
I've also tried the iPad2 and iOS 8.4 with similar results, although there the
item that ticks up and up is "Malloc 64 bytes", at a rate of about 1 KB every 5
seconds. The project is compiled with ARC turned on. The high water mark of
total memory use displayed in XCode increases by a megabyte in something over
an hour and an overnight run shows no sign of it stopping.
But I cannot see what is causing this. It's a very small app, and if I let it
run without interacting with it, the only code it executes is the following
method of the single view controller, invoked by an NSTimer once a second to
update a display of the time.
- (void)updateTime {
NSDate *now = [NSDate date];
double seconds = [now timeIntervalSinceReferenceDate];
double intseconds = round(seconds);
now = [NSDate dateWithTimeIntervalSinceReferenceDate:intseconds];
[dateFormatter setDateFormat:
[NSDateFormatter dateFormatFromTemplate:@"jjmmss" options: 0 locale:
thelocale]];
[[self timestring] setText: [dateFormatter stringFromDate: now]];
[dateFormatter setDateFormat:
[NSDateFormatter dateFormatFromTemplate:@"EEEdMMM" options: 0 locale:
thelocale]];
[[self daystring] setText: [dateFormatter stringFromDate: now]];
[dateFormatter setDateFormat:
[NSDateFormatter dateFormatFromTemplate:@"yyyy" options: 0 locale:
thelocale]];
[[self yearstring] setText: [dateFormatter stringFromDate: now]];
}
timestring, daystring, and yearstring are properties of my ViewController class
connected to labels in the storyboard:
@property (weak, nonatomic) IBOutlet UILabel *timestring;
@property (weak, nonatomic) IBOutlet UILabel *daystring;
@property (weak, nonatomic) IBOutlet UILabel *yearstring;
dateFormatter and thelocale are private instance variables, initialised once in
viewDidLoad(). I've also tried versions where these are variables local to
updateTime(), and where "now" is an instance variable, but moving these around
gives the same results. I've also tried, with equal lack of effect, splitting
up some of the one-liners into things like:
NSString *thestring = [dateFormatter stringFromDate: now];
[[self timestring] setText: thestring];
When the app is in the background it does nothing (it invalidates the NSTimer
and sets the instance variable holding it to NULL), and Allocations reports no
activity.
What is causing this problem? Instruments says the Responsible Library is
libdispatch.dylib, and the Responsible Caller is
_dispatch_continuation_alloc_from_heap. The names suggest that this may be
nothing to do with the code above. Google turns up a small number of queries
regarding memory leaks with similar symptoms, but no answers.
--
Richard Kennaway
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