[iOS] Getting current CPU usage.

cpu-usage.cpp

#include <mach/mach.h>

// http://stackoverflow.com/questions/8223348/ios-get-cpu-usage-from-application
double getCurrentCPUUsage()
{
    thread_array_t         threads;
    mach_msg_type_number_t threadCount;
    if (task_threads(mach_task_self(), &threads, &threadCount) != KERN_SUCCESS) {
        return -1;
    }
    double usage = 0;
    for (int i = 0; i < threadCount; i++) {
        thread_info_data_t     threadInfo;
        mach_msg_type_number_t threadInfoCount = THREAD_INFO_MAX;
        if (thread_info(threads[i], THREAD_BASIC_INFO, (thread_info_t) threadInfo, &threadInfoCount) != KERN_SUCCESS) {
            usage = -1;
            break;
        }
        auto info = (thread_basic_info_t) threadInfo;
        if ((info->flags & TH_FLAGS_IDLE) == 0) {
            usage += double(info->cpu_usage) / TH_USAGE_SCALE;
        }
    }
    vm_deallocate(mach_task_self(), (vm_offset_t) threads, threadCount * sizeof(thread_t));
    return usage;
}

snapshot.mm

#import <UIKit/UIKit.h>

UIImage *takeSnapshot()
{
    UIWindow *window = UIApplication.sharedApplication.windows[0];
    if ([UIScreen.mainScreen respondsToSelector:@selector(scale)]) {
        UIGraphicsBeginImageContextWithOptions(window.bounds.size, NO, UIScreen.mainScreen.scale);
    }
    else {
        UIGraphicsBeginImageContext(window.bounds.size);
    }
    [window.layer renderInContext:UIGraphicsGetCurrentContext()];
    auto image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}