代碼參考：

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface Monitor : NSObject
+ (instancetype)shareInstance;
- (void)startMonitor;
@end

NS_ASSUME_NONNULL_END

#import "Monitor.h"

@interface Monitor()

@property (nonatomic,strong) NSThread *monitorThread;
@property (nonatomic,strong) NSDate *startDate;
@property (nonatomic,assign, getter=isExcuting) BOOL excuting;//是否正在執行任務
@end


@implementation Monitor {
    CFRunLoopObserverRef _observer;//觀察者
    CFRunLoopTimerRef _timer;//定時器
}

+ (instancetype)shareInstance {
    
    static dispatch_once_t once_token;
    static Monitor *monitor;
    dispatch_once(&once_token, ^{
        if (!monitor) {
            monitor = [[Monitor alloc] init];
            monitor.monitorThread = [[NSThread alloc] initWithTarget:self selector:@selector(monitorThreadEntrypoint) object:nil];
            [monitor.monitorThread start];
        }
    });
    return monitor;
}

//創建一個子線程，在線程啟動時，啟動其 Runloop
+ (void)monitorThreadEntrypoint {
    
    @autoreleasepool {
        [[NSThread currentThread] setName:@"minotor"];
        
        [[NSRunLoop currentRunLoop] addPort:[NSPort port] forMode:NSDefaultRunLoopMode];
        [[NSRunLoop currentRunLoop] run];
    }
}

//2 檢測卡頓方法
- (void)startMonitor {
    if(_observer) {
        return;
    }
    //創建 observer
    CFRunLoopObserverContext context = {0,(__bridge void *)self, NULL, NULL, NULL};
    _observer = CFRunLoopObserverCreate(kCFAllocatorDefault, kCFRunLoopAllActivities, YES, 0, &runloopObserverCallBack, &context);
    //將 observer 添加到主線程的 Runloop 中
    CFRunLoopAddObserver(CFRunLoopGetMain(), _observer, kCFRunLoopCommonModes);
    
    //創建一個 Timer，并添加到子線程的 Runloop 中
    [self performSelector:@selector(addTimerToMonitorThread) onThread:self.monitorThread withObject:nil waitUntilDone:NO modes:@[NSRunLoopCommonModes]];
    
}


/// observer 回調
/// 因為主線程中的 block、交互事件、以及其他任務都是在 KCFRunLoopBeforeSources 到 KCFRunLoopBeforeWaiting 之前執行
/// 所以在開始執行 sources 時 ，即 KCFRunLoopBeforeSources 狀態時，記錄一下時間，并把正在執行任務的標記設置為 yes
/// 將要進入睡眠狀態時，即 KCFRunLoopBeforeWaiting 狀態時，將正在執行任務的標記設置為 NO
static void runloopObserverCallBack(CFRunLoopObserverRef observer, CFRunLoopActivity activity, void *info) {
    Monitor *monitor = (__bridge Monitor *)info;
    switch (activity) {
        case kCFRunLoopEntry:
            NSLog(@"kCFRunLoopEntry");
            break;
        case kCFRunLoopBeforeSources:
            NSLog(@"kCFRunLoopBeforeSources");
            monitor.startDate = [NSDate date];
            monitor.excuting = YES;
            break;
        case kCFRunLoopBeforeTimers:
            NSLog(@"kCFRunLoopBeforeTimers");
            break;
        case kCFRunLoopBeforeWaiting:
            NSLog(@"kCFRunLoopBeforeWaiting");
            monitor.excuting = NO;
            break;
        case kCFRunLoopAfterWaiting:
            NSLog(@"kCFRunLoopAfterWaiting");
            break;
        case kCFRunLoopExit:
            NSLog(@"kCFRunLoopExit");
            break;
        case kCFRunLoopAllActivities:
            NSLog(@"kCFRunLoopAllActivities");
            break;
    }
}

///添加定時器到 Runloop 中
- (void)addTimerToMonitorThread {
    
    if (_timer) return;
    
    //創建一個 Timer
    CFRunLoopRef currentRunLoop = CFRunLoopGetCurrent();
    CFRunLoopTimerContext context = {0, (__bridge void *)self, NULL, NULL, NULL};
    
    _timer = CFRunLoopTimerCreate(kCFAllocatorDefault, 0.01, 0.01, 0, 0, &runLoopTimerCallBack, &context);
    
    //添加到子線程的 Runloop 中
    CFRunLoopAddTimer(currentRunLoop, _timer, kCFRunLoopCommonModes);
}

static void runLoopTimerCallBack(CFRunLoopTimerRef timer, void *info) {
    Monitor *monitor = (__bridge Monitor *)info;
    if (!monitor.isExcuting){//即 Runloop 已經進入休眠，kCFRunLoopBeforeWaiting 狀態
        return;
    }
    
    //如果主線程正在執行任務，并且這一次 loop 執行到現在還沒有執行完，那就需要計算時間差
    //即從 kCFRunLoopBeforeSources 狀態到當前狀態的時間差 excuteTime
    NSTimeInterval excuteTime = [[NSDate date] timeIntervalSinceDate:monitor.startDate];
    NSLog(@"定時器：當前線程：%@，主線程執行時間：%f秒",[NSThread currentThread],excuteTime);
    //Timer每 0.1s 執行一次，如果當前正在執行任務的狀態為 YES，并且從開始執行到現在的時間大于閾值，則把堆棧信息保存起來，便于后面處理
    if (excuteTime >= 0.01) {
        NSLog(@"線程卡頓了%f秒",excuteTime);
        [monitor handleStackInfo];
    }
}

//堆棧信息處理
- (void)handleStackInfo {
    //使用第三方CrashReporter 或者其他來打印出堆棧信息
}
@end