Android 流程度評(píng)測(cè)知多少

和你一起終身學(xué)習(xí)，這里是程序員Android

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一、FPS評(píng)測(cè)應(yīng)用流暢度不準(zhǔn)確
二、Choreographer幀率檢測(cè)原理
三、如何檢測(cè)

一、FPS評(píng)測(cè)應(yīng)用流暢度不準(zhǔn)確

說(shuō)到應(yīng)用的流暢度，都會(huì)想到FPS，系統(tǒng)獲取FPS的原理是：手機(jī)屏幕顯示的內(nèi)容是通過(guò)Android系統(tǒng)的SurfaceFLinger類(lèi)，把當(dāng)前系統(tǒng)里所有進(jìn)程需要顯示的信息合成一幀，然后提交到屏幕上進(jìn)行顯示，F(xiàn)PS就是1秒內(nèi)SurfaceFLinger提交到屏幕的幀數(shù)。用FPS來(lái)評(píng)測(cè)一個(gè)應(yīng)用是否真的卡頓存在兩個(gè)問(wèn)題。

• 有的時(shí)候FPS很低，APP看起來(lái)卻很流暢；

• APP停止操作之后，F(xiàn)PS還是在一直變化，這種情況是否會(huì)影響到FPS的準(zhǔn)確度？
  有的時(shí)候FPS很低，APP看起來(lái)卻很流暢，是因?yàn)楫?dāng)前界面在1秒內(nèi)只需要10幀的顯示需求，當(dāng)然不會(huì)卡頓，此時(shí)FPS只要高于10就可以了，如果屏幕根本沒(méi)有繪制需求，那FPS的值就是0。

Android性能優(yōu)化第（四）篇---Android渲染機(jī)制說(shuō)過(guò)，Android系統(tǒng)每隔16ms發(fā)出VSYNC信號(hào)，觸發(fā)對(duì)UI的渲染，16ms沒(méi)完成繪制就會(huì)卡頓。VSync機(jī)制就像是一臺(tái)轉(zhuǎn)速固定的發(fā)動(dòng)機(jī)(60轉(zhuǎn)/s)。每一轉(zhuǎn)會(huì)帶動(dòng)著去做一些UI相關(guān)的事情，但不是每一轉(zhuǎn)都會(huì)有工作去做(就像有時(shí)在空擋，有時(shí)在D檔)。有時(shí)候因?yàn)楦鞣N阻力某一圈工作量比較重超過(guò)了16.6ms，那么這臺(tái)發(fā)動(dòng)機(jī)這秒內(nèi)就不是60轉(zhuǎn)了，當(dāng)然也有可能被其他因素影響，比如給油不足(主線程里干的活太多)等等，就會(huì)出現(xiàn)轉(zhuǎn)速降低的狀況。我們把這個(gè)轉(zhuǎn)速叫做流暢度。當(dāng)流暢度越小的時(shí)候說(shuō)明當(dāng)前程序越卡頓。

二、Choreographer幀率檢測(cè)原理

我們有時(shí)候會(huì)看到這樣的log，系統(tǒng)幫助我們打印出了跳幀數(shù)。

02-07 19:47:04.333 17601-17604/zhangwan.wj.com.choreographertest D/dalvikvm: GC_CONCURRENT freed 143K, 3% free 9105K/9384K, paused 2ms+0ms, total 6ms
02-07 19:47:04.337 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 60 frames!  The application may be doing too much work on its main thread.
02-07 19:47:11.685 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 85 frames!  The application may be doing too much work on its main thread.
02-07 19:47:12.545 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 37 frames!  The application may be doing too much work on its main thread.
02-07 19:47:14.893 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 37 frames!  The application may be doing too much work on its main thread.
02-07 19:47:23.049 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 36 frames!  The application may be doing too much work on its main thread.
02-07 19:47:23.929 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 37 frames!  The application may be doing too much work on its main thread.
02-07 19:47:24.961 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 61 frames!  The application may be doing too much work on its main thread.
02-07 19:47:25.817 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 36 frames!  The application may be doing too much work on its main thread.
02-07 19:47:26.433 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 36 frames!  The application may be doing too much work on its main thread.

這個(gè)log就出自于Choreographer中（英[?k?r?'?ɡr?f?(r)] 美[?k?r?'?ɡr?f?(r)]）。

void doFrame(long frameTimeNanos, int frame) {
        final long startNanos;
        synchronized (mLock) {
            if (!mFrameScheduled) {
                return; // no work to do
            }

            if (DEBUG_JANK && mDebugPrintNextFrameTimeDelta) {
                mDebugPrintNextFrameTimeDelta = false;
                Log.d(TAG, "Frame time delta: "
                        + ((frameTimeNanos - mLastFrameTimeNanos) * 0.000001f) + " ms");
            }

            long intendedFrameTimeNanos = frameTimeNanos;
            startNanos = System.nanoTime();
            final long jitterNanos = startNanos - frameTimeNanos;
            if (jitterNanos >= mFrameIntervalNanos) {
                final long skippedFrames = jitterNanos / mFrameIntervalNanos;
                if (skippedFrames >= SKIPPED_FRAME_WARNING_LIMIT) {
                    Log.i(TAG, "Skipped " + skippedFrames + " frames!  "
                            + "The application may be doing too much work on its main thread.");
                }
                final long lastFrameOffset = jitterNanos % mFrameIntervalNanos;
                if (DEBUG_JANK) {
                    Log.d(TAG, "Missed vsync by " + (jitterNanos * 0.000001f) + " ms "
                            + "which is more than the frame interval of "
                            + (mFrameIntervalNanos * 0.000001f) + " ms!  "
                            + "Skipping " + skippedFrames + " frames and setting frame "
                            + "time to " + (lastFrameOffset * 0.000001f) + " ms in the past.");
                }
                frameTimeNanos = startNanos - lastFrameOffset;
            }
        }

    }

其中SKIPPED_FRAME_WARNING_LIMIT是Choreographer的成員變量。

  // Set a limit to warn about skipped frames.
  // Skipped frames imply jank.
  private static final int SKIPPED_FRAME_WARNING_LIMIT =SystemProperties.getInt( "debug.choreographer.skipwarning", 30);

也就是當(dāng)跳幀數(shù)大于設(shè)置的SKIPPED_FRAME_WARNING_LIMIT 值時(shí)會(huì)在當(dāng)前進(jìn)程輸出這個(gè)log。由于 SKIPPED_FRAME_WARNING_LIMIT 的值默認(rèn)為 30，所以上面的log并不是經(jīng)?？吹剑绻覀冇梅瓷涞姆椒ò裇KIPPED_FRAME_WARNING_LIMIT的值設(shè)置成1，這樣可以保證只要有丟幀，就會(huì)有上面的log輸出來(lái)。

static {
        try {
            Field field = Choreographer.class.getDeclaredField("SKIPPED_FRAME_WARNING_LIMIT");
            field.setAccessible(true);
            field.set(Choreographer.class,1);
        } catch (Throwable e) {
            e.printStackTrace();
        }
    }

注意，這個(gè)方案是 API 16 以上才支持。Choreographer就是一個(gè)消息處理器，根據(jù)vsync 信號(hào) 來(lái)計(jì)算frame，而計(jì)算frame的方式就是處理三種回調(diào)，包括事件回調(diào)、動(dòng)畫(huà)回調(diào)、繪制回調(diào)。這三種事件在消息輸入、加入動(dòng)畫(huà)、準(zhǔn)備繪圖layout 等動(dòng)作時(shí)均會(huì)發(fā)給Choreographer。一句話，我們只要捕獲這個(gè)log提取出skippedFrames 就可以知道界面是否卡頓。

三、如何檢測(cè)

采用上面的方式就可以在App內(nèi)部觀測(cè)當(dāng)前App的流暢度了。并且在丟幀的地方打印，就可以知道丟幀的大概原因，大概位置，定位代碼問(wèn)題。

在Choreographer中有個(gè)回調(diào)接口，F(xiàn)rameCallback。

public interface FrameCallback {  
  //當(dāng)新的一幀被繪制的時(shí)候被調(diào)用。
   public void doFrame(long frameTimeNanos);
}

根據(jù)上面的代碼，重寫(xiě)doFrame方法，所以照葫蘆畫(huà)瓢，自定義FrameCallback。我們可以在每一幀被渲染的時(shí)候記錄下它開(kāi)始渲染的時(shí)間，這樣在下一幀被處理時(shí)，判斷上一幀在渲染過(guò)程中是否出現(xiàn)掉幀。

public class SMFrameCallback implements Choreographer.FrameCallback {

    public static  SMFrameCallback sInstance;

    private String TAG="SMFrameCallback";

    public static final float deviceRefreshRateMs=16.6f;

    public static  long lastFrameTimeNanos=0;//納秒為單位

    public static  long currentFrameTimeNanos=0;

    public void start() {
        Choreographer.getInstance().postFrameCallback(SMFrameCallback.getInstance());
    }

    public static SMFrameCallback getInstance() {
        if (sInstance == null) {
            sInstance = new SMFrameCallback();
        }
        return sInstance;
    }

    @Override
    public void doFrame(long frameTimeNanos) {
        if(lastFrameTimeNanos==0){
            lastFrameTimeNanos=frameTimeNanos;
            Choreographer.getInstance().postFrameCallback(this);
            return;
        }
        currentFrameTimeNanos=frameTimeNanos;
        float value=(currentFrameTimeNanos-lastFrameTimeNanos)/1000000.0f;

        final int skipFrameCount = skipFrameCount(lastFrameTimeNanos, currentFrameTimeNanos, deviceRefreshRateMs);
        Log.e(TAG,"兩次繪制時(shí)間間隔value="+value+"  frameTimeNanos="+frameTimeNanos+"  currentFrameTimeNanos="+currentFrameTimeNanos+"  skipFrameCount="+skipFrameCount+"");
        lastFrameTimeNanos=currentFrameTimeNanos;
        Choreographer.getInstance().postFrameCallback(this);
    }

    /**
     *
     *計(jì)算跳過(guò)多少幀
     * @param start
     * @param end
     * @param devicefreshRate
     * @return
     */
    private  int skipFrameCount(long start,long end,float devicefreshRate){
        int count =0;
        long diffNs=end-start;
        long diffMs = Math.round(diffNs / 1000000.0f);
        long dev=Math.round(devicefreshRate);
        if(diffMs>dev){
            long skipCount=diffMs/dev;
            count=(int)skipCount;
        }
        return  count;
    }
}

在需要檢測(cè)的Activity中調(diào)用 SMFrameCallback.getInstance().start()即可。一般優(yōu)化一下，可以在BaseActivity去調(diào)用或者Activitylifecyclecallbacks中去調(diào)用.
正常情況下輸出的日志是：

02-07 20:18:52.605 6683-6683/zhangwan.wj.com.choreographertest E/SMFrameCallback: 兩次繪制時(shí)間間隔value=16.666666  frameTimeNanos=6996166386820  currentFrameTimeNanos=6996166386820  skipFrameCount=0
02-07 20:18:52.621 6683-6683/zhangwan.wj.com.choreographertest E/SMFrameCallback: 兩次繪制時(shí)間間隔value=16.666666  frameTimeNanos=6996183053486  currentFrameTimeNanos=6996183053486  skipFrameCount=0
02-07 20:18:52.637 6683-6683/zhangwan.wj.com.choreographertest E/SMFrameCallback: 兩次繪制時(shí)間間隔value=16.666666  frameTimeNanos=6996199720152  currentFrameTimeNanos=6996199720152  skipFrameCount=0
02-07 20:18:52.657 6683-6683/zhangwan.wj.com.choreographertest E/SMFrameCallback: 兩次繪制時(shí)間間隔value=16.666666  frameTimeNanos=6996216386818  currentFrameTimeNanos=6996216386818  skipFrameCount=0
02-07 20:18:52.673 6683-6683/zhangwan.wj.com.choreographertest E/SMFrameCallback: 兩次繪制時(shí)間間隔value=16.666666  frameTimeNanos=6996233053484  currentFrameTimeNanos=6996233053484  skipFrameCount=0
02-07 20:18:52.689 6683-6683/zhangwan.wj.com.choreographertest E/SMFrameCallback: 兩次繪制時(shí)間間隔value=16.666666  frameTimeNanos=6996249720150  currentFrameTimeNanos=6996249720150  skipFrameCount=0

有跳幀的時(shí)候輸出的日志是

02-07 20:21:53.909 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 兩次繪制時(shí)間間隔value=16.666666  frameTimeNanos=7177466379568  currentFrameTimeNanos=7177466379568  skipFrameCount=0
02-07 20:21:53.925 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 兩次繪制時(shí)間間隔value=16.666666  frameTimeNanos=7177483046234  currentFrameTimeNanos=7177483046234  skipFrameCount=0
02-07 20:21:54.133 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 兩次繪制時(shí)間間隔value=200.0  frameTimeNanos=7177683046226  currentFrameTimeNanos=7177683046226  skipFrameCount=11
02-07 20:21:54.745 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 兩次繪制時(shí)間間隔value=616.6666  frameTimeNanos=7178299712868  currentFrameTimeNanos=7178299712868  skipFrameCount=36
02-07 20:21:54.757 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 兩次繪制時(shí)間間隔value=16.666666  frameTimeNanos=7178316379534  currentFrameTimeNanos=7178316379534  skipFrameCount=0
02-07 20:21:54.773 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 兩次繪制時(shí)間間隔value=16.666666  frameTimeNanos=7178333046200  currentFrameTimeNanos=7178333046200  skipFrameCount=0
02-07 20:21:54.789 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 兩次繪制時(shí)間間隔value=16.666666  frameTimeNanos=7178349712866  currentFrameTimeNanos=7178349712866  skipFrameCount=0

看到兩次繪制的時(shí)間間隔相差616.6666毫秒，跳過(guò)了36幀，這個(gè)卡頓用戶是能夠明顯感知的

參考鏈接：https://www.jianshu.com/p/d126640eccb1

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