Watching memory usage in iOS

While testing and debugging your app with XCode you can use this logMemUsage() function to NSLog the used/free space and watch how things are going while you test your app. This function logs any change in usage > 100kb. It outputs to the debug log like this (on the simulator the free space is huge):

2011-11-02 21:55:58.928 hello[971:207] Memory used 21884.9 (+21885), free 1838366.8 kb2011-11-02 21:55:59.936 hello[971:207] Memory used 28512.3 (+6627), free 1830809.6 kb2011-11-02 21:56:01.936 hello[971:207] Memory used 28803.1 ( +291), free 1830129.6 kb2011-11-02 21:56:02.936 hello[971:207] Memory used 29712.4 ( +909), free 1830142.0 kb

You decide where to call logMemUsage in your app. I happen to have a function that is called by a timer every second and so I put it in there. I suggest using #ifdef around these so this code is only included in Debug builds.

#import "mach/mach.h" vm_size_t usedMemory(void) {    struct task_basic_info info;    mach_msg_type_number_t size = sizeof(info);    kern_return_t kerr = task_info(mach_task_self(), TASK_BASIC_INFO, (task_info_t)&info, &size);    return (kerr == KERN_SUCCESS) ? info.resident_size : 0; // size in bytes}vm_size_t freeMemory(void) {    mach_port_t host_port = mach_host_self();    mach_msg_type_number_t host_size = sizeof(vm_statistics_data_t) / sizeof(integer_t);    vm_size_t pagesize;    vm_statistics_data_t vm_stat;    host_page_size(host_port, &pagesize);    (void) host_statistics(host_port, HOST_VM_INFO, (host_info_t)&vm_stat, &host_size);    return vm_stat.free_count * pagesize;}void logMemUsage(void) {    // compute memory usage and log if different by >= 100k    static long prevMemUsage = 0;    long curMemUsage = usedMemory();    long memUsageDiff = curMemUsage - prevMemUsage;    if (memUsageDiff > 100000 || memUsageDiff < -100000) {        prevMemUsage = curMemUsage;        NSLog(@"Memory used %7.1f (%+5.0f), free %7.1f kb", curMemUsage/1000.0f, memUsageDiff/1000.0f, freeMemory()/1000.0f);    }}

Actually each view controller has - (void)didReceiveMemoryWarning functions.

- (void)didReceiveMemoryWarning{    // Releases the view if it doesn't have a superview.    [super didReceiveMemoryWarning];    // Release any cached data, images, etc that aren't in use.}

As suggested by the comments, you can release unused data under the comment. On the other hand, comment out [super didReceiveMemoryWarning]; to suppress memory warnings & auto release objects.

First the title of your question is how to watch memory usage in iOS..There is a tool called instrument comes with xcode, which you can use to track memory allocation, leaks, cpu usage and a host of other things..See apple's documentation on the subject..

• Now to see the real time memory usage of your app you can useallocator tool in instrument
• To identify the memory leaks you can use leak tool in instrument..

Also in WWDC 2010 there is a video of how to analyze memory using Instrument..