Get CPU percent usage on macOS

Question

I'm a beginner in Objective-C, and I decided to try to write some simple application, so I'm trying to make an app which would measure CPU usage and such. Is there a simple way to get information such as the CPU percent usage using Objective-C in a Cocoa application?

I have found this question Determine Process Info Programmatically in Darwin/OSX which is similar, but not exactly the same. Mainly, I want the CPU percent usage of the whole system, not just my process, and I would actually prefer an Objective-C solution whereas in that question the poster wanted something else.

Answer 1

Here is the way i did it:

*.h file:

#include <sys/sysctl.h>
#include <sys/types.h>
#include <mach/mach.h>
#include <mach/processor_info.h>
#include <mach/mach_host.h>

ivars:

processor_info_array_t cpuInfo, prevCpuInfo;
mach_msg_type_number_t numCpuInfo, numPrevCpuInfo;
unsigned numCPUs;
NSTimer *updateTimer;
NSLock *CPUUsageLock;

*.m file

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{    
    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];

    updateTimer = [[NSTimer scheduledTimerWithTimeInterval:3
                                                    target:self
                                                  selector:@selector(updateInfo:)
                                                  userInfo:nil
                                                   repeats:YES] retain];    
}

- (void)updateInfo:(NSTimer *)timer
{
    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) {
            float 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];
            }

            NSLog(@"Core: %u Usage: %f",i,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 = NULL;
        numCpuInfo = 0U;
    } else {
        NSLog(@"Error!");
        [NSApp terminate:nil];
    }
}

Answer 2

Swift 4 equivalent of VenoMKO answer. Usage: let myUsage = MyCpuUsage() to start the usage observation. Tested with Xcode 10.0.

import Foundation

// CPU usage credit VenoMKO: https://stackoverflow.com/a/6795612/1033581
class MyCpuUsage {
    var cpuInfo: processor_info_array_t!
    var prevCpuInfo: processor_info_array_t?
    var numCpuInfo: mach_msg_type_number_t = 0
    var numPrevCpuInfo: mach_msg_type_number_t = 0
    var numCPUs: uint = 0
    var updateTimer: Timer!
    let CPUUsageLock: NSLock = NSLock()

    init() {
        let mibKeys: [Int32] = [ CTL_HW, HW_NCPU ]
        // sysctl Swift usage credit Matt Gallagher: https://github.com/mattgallagher/CwlUtils/blob/master/Sources/CwlUtils/CwlSysctl.swift
        mibKeys.withUnsafeBufferPointer() { mib in
            var sizeOfNumCPUs: size_t = MemoryLayout<uint>.size
            let status = sysctl(processor_info_array_t(mutating: mib.baseAddress), 2, &numCPUs, &sizeOfNumCPUs, nil, 0)
            if status != 0 {
                numCPUs = 1
            }
            updateTimer = Timer.scheduledTimer(timeInterval: 3, target: self, selector: #selector(updateInfo), userInfo: nil, repeats: true)
        }
    }

    @objc func updateInfo(_ timer: Timer) {
        var numCPUsU: natural_t = 0
        let err: kern_return_t = host_processor_info(mach_host_self(), PROCESSOR_CPU_LOAD_INFO, &numCPUsU, &cpuInfo, &numCpuInfo);
        if err == KERN_SUCCESS {
            CPUUsageLock.lock()

            for i in 0 ..< Int32(numCPUs) {
                var inUse: Int32
                var total: Int32
                if let prevCpuInfo = prevCpuInfo {
                    inUse = cpuInfo[Int(CPU_STATE_MAX * i + CPU_STATE_USER)]
                        - prevCpuInfo[Int(CPU_STATE_MAX * i + CPU_STATE_USER)]
                        + cpuInfo[Int(CPU_STATE_MAX * i + CPU_STATE_SYSTEM)]
                        - prevCpuInfo[Int(CPU_STATE_MAX * i + CPU_STATE_SYSTEM)]
                        + cpuInfo[Int(CPU_STATE_MAX * i + CPU_STATE_NICE)]
                        - prevCpuInfo[Int(CPU_STATE_MAX * i + CPU_STATE_NICE)]
                    total = inUse + (cpuInfo[Int(CPU_STATE_MAX * i + CPU_STATE_IDLE)]
                        - prevCpuInfo[Int(CPU_STATE_MAX * i + CPU_STATE_IDLE)])
                } else {
                    inUse = cpuInfo[Int(CPU_STATE_MAX * i + CPU_STATE_USER)]
                        + cpuInfo[Int(CPU_STATE_MAX * i + CPU_STATE_SYSTEM)]
                        + cpuInfo[Int(CPU_STATE_MAX * i + CPU_STATE_NICE)]
                    total = inUse + cpuInfo[Int(CPU_STATE_MAX * i + CPU_STATE_IDLE)]
                }

                print(String(format: "Core: %u Usage: %f", i, Float(inUse) / Float(total)))
            }
            CPUUsageLock.unlock()

            if let prevCpuInfo = prevCpuInfo {
                // vm_deallocate Swift usage credit rsfinn: https://stackoverflow.com/a/48630296/1033581
                let prevCpuInfoSize: size_t = MemoryLayout<integer_t>.stride * Int(numPrevCpuInfo)
                vm_deallocate(mach_task_self_, vm_address_t(bitPattern: prevCpuInfo), vm_size_t(prevCpuInfoSize))
            }

            prevCpuInfo = cpuInfo
            numPrevCpuInfo = numCpuInfo

            cpuInfo = nil
            numCpuInfo = 0
        } else {
            print("Error!")
        }
    }
}