• FPS監控：因為iOS裝置螢幕的重新整理時間是60次/秒，一次重新整理就是一次VSync訊號，時間間隔是1000ms/60 = 16.67ms，所有如果咋16.67ms內下一幀資料沒有準備好，就會產生掉幀
• RunLoop監控：通過子執行緒檢測主執行緒的RunLoop的狀態，kCFRunLoopBeforeSources和kCFRunLoopAfterWaiting兩個狀態之間的耗時是否達到一定的閾值

FPS監控

參照YYKit中的YYFPSLabel，其中通過CADisplayLink來實現，通過重新整理次數/時間差得到重新整理頻率

class YPFPSLabel: UILabel {

    fileprivate 
 
var link: CADisplayLink = {
        let link = CADisplayLink.init()
        return link
    }()
    
    fileprivate var count: Int = 0
    fileprivate var lastTime: TimeInterval = 0.0
    fileprivate var fpsColor: UIColor = {
        return UIColor.green
    }()
    fileprivate var fps: Double = 0.0
    
    override
 
 init(frame: CGRect) {
        var f = frame
        if f.size == CGSize.zero {
            f.size = CGSize(width: 80.0, height: 22.0)
        }
        
        super.init(frame: f)
        
        self.textColor = UIColor.white
        self.textAlignment = .center
        self.font = UIFont.init(name: "
 
Menlo", size: 12)
        self.backgroundColor = UIColor.lightGray
        //通過虛擬類
        link = CADisplayLink.init(target: CJLWeakProxy(target:self), selector: #selector(tick(_:)))
        link.add(to: RunLoop.current, forMode: RunLoop.Mode.common)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    deinit {
        link.invalidate()
    }
    
    @objc func tick(_ link: CADisplayLink){
        guard lastTime != 0 else {
            lastTime = link.timestamp
            return
        }
        
        count += 1
        //時間差
        let detla = link.timestamp - lastTime
        guard detla >= 1.0 else {
            return
        }
        
        lastTime = link.timestamp
        //重新整理次數 / 時間差 = 重新整理頻次
        fps = Double(count) / detla
        let fpsText = "\(String.init(format: "%.2f", fps)) FPS"
        count = 0
        
        let attrMStr = NSMutableAttributedString(attributedString: NSAttributedString(string: fpsText))
        if fps > 55.0 {
            //流暢
            fpsColor = UIColor.green
        }else if (fps >= 50.0 && fps <= 55.0){
            //一般
            fpsColor = UIColor.yellow
        }else{
            //卡頓
            fpsColor = UIColor.red
        }
        
        attrMStr.setAttributes([NSAttributedString.Key.foregroundColor: fpsColor], range: NSMakeRange(0, attrMStr.length - 3))
        attrMStr.setAttributes([NSAttributedString.Key.foregroundColor: UIColor.white], range: NSMakeRange(attrMStr.length - 3, 3))
        
        DispatchQueue.main.async {
            self.attributedText = attrMStr
        }
    }

}

RunLoop監控

參考 微信的matrix，滴滴的DoraemonKit

開闢子執行緒，通過監聽主執行緒的kCFRunLoopBeforeSources和kCFRunLoopAfterWaiting兩個Activity之間的差值

#import "YPBlockMonitor.h"

@interface YPBlockMonitor (){
    CFRunLoopActivity activity;
}

@property (nonatomic, strong) dispatch_semaphore_t semaphore;
@property (nonatomic, assign) NSUInteger timeoutCount;

@end

@implementation YPBlockMonitor

+ (instancetype)sharedInstance {
    static id instance = nil;
    static dispatch_once_t onceToken;
    
    dispatch_once(&onceToken, ^{
        instance = [[self alloc] init];
    });
    return instance;
}

- (void)start{
    [self registerObserver];
    [self startMonitor];
}

static void CallBack(CFRunLoopObserverRef observer, CFRunLoopActivity activity, void *info)
{
    LGBlockMonitor *monitor = (__bridge LGBlockMonitor *)info;
    monitor->activity = activity;
    // 傳送訊號
    dispatch_semaphore_t semaphore = monitor->_semaphore;
    dispatch_semaphore_signal(semaphore);
}

- (void)registerObserver{
    CFRunLoopObserverContext context = {0,(__bridge void*)self,NULL,NULL};
    //NSIntegerMax : 優先順序最小
    CFRunLoopObserverRef observer = CFRunLoopObserverCreate(kCFAllocatorDefault,
                                                            kCFRunLoopAllActivities,
                                                            YES,
                                                            NSIntegerMax,
                                                            &CallBack,
                                                            &context);
    CFRunLoopAddObserver(CFRunLoopGetMain(), observer, kCFRunLoopCommonModes);
}

- (void)startMonitor{
    // 建立訊號
    _semaphore = dispatch_semaphore_create(0);
    // 在子執行緒監控時長
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        while (YES)
        {
            // 超時時間是 1 秒，沒有等到訊號量，st 就不等於 0， RunLoop 所有的任務
            long st = dispatch_semaphore_wait(self->_semaphore, dispatch_time(DISPATCH_TIME_NOW, 1 * NSEC_PER_SEC));
            if (st != 0)
            {
                if (self->activity == kCFRunLoopBeforeSources || self->activity == kCFRunLoopAfterWaiting)
                {
                    if (++self->_timeoutCount < 2){
                        NSLog(@"timeoutCount==%lu",(unsigned long)self->_timeoutCount);
                        continue;
                    }
                    // 一秒左右的衡量尺度 很大可能性連續來 避免大規模列印!
                    NSLog(@"檢測到超過兩次連續卡頓");
                }
            }
            self->_timeoutCount = 0;
        }
    });
}

@end

轉自：https://www.jianshu.com/p/2f9a06932879