How to get iOS CPU Core usage? - ios

Question

There has been a lot of the same question, but yet I cannot find great answers. I've looked at codes from this particular post which gives me usage per core, but it is inaccurate, always stuck at 14% or so even when Instrument tells me one core is under full load (primality test!).
I also read this question which I actually got the code from.
I have little knowledge of sysctl, which seems to be the key for these kind of things. Can someone explain to me how I could achieve that, code example will be even more appreciated. Thanks!
This is my current code, it was ran on a separate thread, which I just realized could be a problem, can anyone confirm? (I use NSThread and NSNotificationCenter to send usage information to main thread.)
- (void)updateCPUUsage
{
NSMutableArray* arrayOfCPUUsage = [NSMutableArray array];
while ( 1 )
{
processor_info_array_t _cpuInfo, _prevCPUInfo = nil;
mach_msg_type_number_t _numCPUInfo, _numPrevCPUInfo = 0;
unsigned _numCPUs;
NSLock *_cpuUsageLock;
int _mib[2U] = { CTL_HW, HW_NCPU };
size_t _sizeOfNumCPUs = sizeof(_numCPUs);
int _status = sysctl(_mib, 2U, &_numCPUs, &_sizeOfNumCPUs, NULL, 0U);
if(_status)
_numCPUs = 1;
_cpuUsageLock = [[NSLock alloc] init];
natural_t _numCPUsU = 0U;
kern_return_t err = host_processor_info(mach_host_self(), PROCESSOR_CPU_LOAD_INFO, &_numCPUsU, &_cpuInfo, &_numCPUInfo);
if(err == KERN_SUCCESS) {
[_cpuUsageLock lock];
for(unsigned i = 0U; i < _numCPUs; ++i) {
Float32 _inUse, _total;
if(_prevCPUInfo) {
_inUse = (
(_cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_USER] - _prevCPUInfo[(CPU_STATE_MAX * i) + CPU_STATE_USER])
+ (_cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_SYSTEM] - _prevCPUInfo[(CPU_STATE_MAX * i) + CPU_STATE_SYSTEM])
+ (_cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_NICE] - _prevCPUInfo[(CPU_STATE_MAX * i) + CPU_STATE_NICE])
);
_total = _inUse + (_cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_IDLE] - _prevCPUInfo[(CPU_STATE_MAX * i) + CPU_STATE_IDLE]);
} else {
_inUse = _cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_USER] + _cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_SYSTEM] + _cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_NICE];
_total = _inUse + _cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_IDLE];
}
[arrayOfCPUUsage addObject:#(_inUse / _total)];
}
[_cpuUsageLock unlock];
if(_prevCPUInfo) {
size_t prevCpuInfoSize = sizeof(integer_t) * _numPrevCPUInfo;
vm_deallocate(mach_task_self(), (vm_address_t)_prevCPUInfo, prevCpuInfoSize);
}
_prevCPUInfo = _cpuInfo;
_numPrevCPUInfo = _numCPUInfo;
_cpuInfo = nil;
_numCPUInfo = 0U;
}
[[NSNotificationCenter defaultCenter] postNotification:[NSNotification notificationWithName:#"CPUUsageUpdate" object:[arrayOfCPUUsage copy]]];
[arrayOfCPUUsage removeAllObjects];
usleep(1000);
}
}