iOS: Tracking amount of allocated objects - ios

Question

We can use instruments for various kinds of analysis. But many programmers find this tool to be too complicated and too heavy to bring real value.
Is there a simple way to track all objects of a specific class, and for each to know who exactly was allocating them and to verify that they are being freed correctly?
The answer is yes! there is a way, and I'll demo it in my answer below

Answer 1

Tracking allocations easily:
How to use: you can put the 150 lines of code below into a file named AllocTracker.m and drag it into your project files.
Use the check box at the right pane of Xcode to enable/disable it in your compilation target.
What you'll get?
when enabled, this module will track all allocations and deallocations of UIImage objects and log them. (It can easily be modified for tracking other classes.)
In addition to logging every allocation and deallocation, it will periodically (currently every 15 seconds) dump all objects which are currently allocated, with some added info and the call stack which allocated them.
What is the added value?
This code was used in big projects to get rid of orphan objects which were left allocated without notice, allowing to significantly reduce the memory footprint of the app and fix memory leaks.
So here is the code for AllocTracker.m:
#define TRACK_ALLOCATIONS
#ifdef TRACK_ALLOCATIONS
#import <UIKit/UIKit.h>
#define TIMER_INTERVAL 15
#implementation UIApplication(utils)
+(NSString *)dateToTimestamp:(NSDate *)date
{
if (date == nil) {
date = [NSDate date];
}
static NSDateFormatter *dateFormatter = nil;
if (!dateFormatter) {
dateFormatter = [[NSDateFormatter alloc] init];
dateFormatter.locale = [[NSLocale alloc] initWithLocaleIdentifier:#"en_US_POSIX"];
[dateFormatter setDateFormat:#"HH:mm:ss.S"];
}
NSString *ts = [dateFormatter stringFromDate:date];
return ts;
}
+(NSString*) getCaller:(int)stackDepth
{
#ifndef DEBUG
return #"NON DBG";
#else
NSArray *symbols = [NSThread callStackSymbols];
int lastIndex = (int)(symbols.count - 1);
if (lastIndex < 3) {
return #"NO DATA";
}
NSMutableString *result = [NSMutableString string];
int foundCount = 0;
for (int ix=3; ix <= lastIndex; ix++) {
NSString *line = symbols[ix];
NSRange rng1 = [line rangeOfString:#"["];
if (rng1.location == NSNotFound) {
continue;
}
NSRange rng2 = [line rangeOfString:#"]"];
NSString *caller = [line substringWithRange:NSMakeRange(rng1.location+1, rng2.location-rng1.location-1)];
if (foundCount > 0) { //not first
[result appendString:#"<--"];
}
[result appendString:caller];
if (++foundCount == stackDepth) {
break;
}
}
return (foundCount > 0) ? result : #"NO SYMBOL";
#endif
}
#end
#implementation UIImage(memoryTrack)
static NSMapTable *g_allocsMap;
static NSTimer *g_tmr;
static NSDate *g_lastDump = nil;
+(void)gotTimer:(NSTimer *)timer
{
[self dumpAllocs];
}
+(void)startTimer
{
static int count = 0;
g_tmr = [NSTimer scheduledTimerWithTimeInterval:15 target:self selector:#selector(gotTimer:) userInfo:#(count++) repeats:YES];
NSLog(#"starting timer %i", count);
}
+(void)cancelTimer
{
[g_tmr invalidate];
g_tmr = nil;
}
+(void)dumpAllocs
{
dispatch_async(dispatch_get_global_queue(QOS_CLASS_BACKGROUND, 0), ^{
NSMutableString *str = [NSMutableString string];
[str appendString:#"\n#$# ========== Non-freed UIImages =========\n"];
NSMutableArray *sorted = [NSMutableArray array];
//make sure map is not changed while enumerating
static int s_ts_start = -1;
#synchronized (g_allocsMap) {
NSEnumerator *keysEnum = [g_allocsMap keyEnumerator];
UIImage *img;
while (img = [keysEnum nextObject]) {
NSString *value = [g_allocsMap objectForKey:img];
if (value) { //might be nulled because declared as weak
NSUInteger memUsed = CGImageGetHeight(img.CGImage) * CGImageGetBytesPerRow(img.CGImage);
NSString *objData = [NSString stringWithFormat:#"mem=%5ikb, size=%4ix%-4i", (int)(memUsed/1024), (int)img.size.width, (int)img.size.height];
NSString *line = [NSString stringWithFormat:#"%p - %# [%#]\n", img, objData, value];
if (s_ts_start<0) {
s_ts_start = (int)[line rangeOfString:#"["].location + 1;
}
if (line.length > (s_ts_start+10)) {
[sorted addObject:line];
}
}
}
}
if (sorted.count > 0) {
[sorted sortUsingComparator: ^NSComparisonResult(NSString *s1, NSString *s2)
{
//we expect '0x15a973700 - mem=3600kb, size=640x360 [16:14:27.5: UIIma...'
NSString *ts1 = [s1 substringWithRange:NSMakeRange(s_ts_start, 10)];
NSString *ts2 = [s2 substringWithRange:NSMakeRange(s_ts_start, 10)];
return [ts1 compare:ts2];
}];
int ix = 0;
for (NSString *line in sorted) {
[str appendFormat:#"#$# %3i) %#", ix++, line];
}
}
[str appendString:#"#$# ======================================================\n"];
NSLog(#"%#", str);
});
}
+(instancetype)alloc
{
NSString *caller = [UIApplication getCaller:4];
#synchronized (self) {
id obj = [super alloc];
NSLog(#"#$# UIImage alloc: [%p], caller=[%#]", obj, caller);
NSDate *now = [NSDate date];
NSString *value = [NSString stringWithFormat:#"%#: %#", [UIApplication dateToTimestamp:now], caller];
if (!g_allocsMap) {
g_allocsMap = [NSMapTable mapTableWithKeyOptions:NSMapTableWeakMemory valueOptions:NSMapTableStrongMemory];
}
[g_allocsMap setObject:value forKey:obj];
if (!g_lastDump) {
[self startTimer];
g_lastDump = now;
}
return obj;
}
}
-(void)dealloc
{
NSLog(#"#$# UIImage dealloc: [%#]", self);
}
#end
#endif //TRACK_ALLOCATIONS
How it works?
We create a category of UIImage and set our own version for alloc and dealloc. Every allocated object is saved into an NSMapTable object which works like a dictionary but allow storing object with weak pointers.
For convenience we were adding two methods under UIApplication which can be used by other modules if an appropriate header file is created. One method is for formatting the timestamp, and the other is for reading the call stack (only works in debug builds).
Tip for use:
if you use a real device and install idevicesyslog (brew install libimobiledevice), you can use the terminal to see all allocation debug, like this:
idevicesyslog | grep "#\$#"