App层面监控卡顿


1、 利用UI线程的Looper打印的日志匹配

2、 使用Choreographer.FrameCallback

Looper比较适合在发布前进行测试或者小范围灰度测试然后定位问题，ChoreographerHelper适合监控线上环境的 app 的掉帧情况来计算 app 在某些场景的流畅度然后有针对性的做性能优化。

一、Looper日志检测卡顿(其实这种方式也就是 BlockCanary 原理)

Android主线程更新UI。如果界面1秒钟刷新少于60次，即FPS小于60，用户就会产生卡顿感觉。简单来说，Android使用消息机制进行UI更新，UI线程有个Looper，在其loop方法中会不断取出message，调用其绑定的Handler在UI线程执行。如果在handler的dispatchMesaage方法里有耗时操作，就会发生卡顿。

public static void loop(){
//......
for(;;){
//......
Printer logging=me.mLogging;
if(logging!=null){
logging.println(">>>>> Dispatching to "+msg.target+" "+msg.callback+": "+msg.what);
}
msg.target.dispatchMessage(msg);
if(logging!=null){
logging.println("<<<<< Finished to "+msg.target+" "+msg.callback);
}
}
}

只要检测 msg.target.dispatchMessage(msg) 的执行时间，就能检测到部分UI线程是否有耗时的操作。注意到这行执行代码的前后，有两个logging.println函数，如果设置了logging，会分别打印出>>>>> Dispatching to和<<<<< Finished to 这样的日志，这样我们就可以通过两次log的时间差值，来计算ispatchMessage的执行时间，从而设置阈值判断是否发生了卡顿。

Looper 提供了 setMessageLogging(@Nullable Printer printer) 方法，所以我们可以自己实现一个Printer，再通过setMessageLogging()方法传入即可

public class BlockCanary {
public static void install() {
MyPrinter myPrinter = new MyPrinter();
Looper.getMainLooper().setMessageLogging(myPrinter);
}
}
public class MyPrinter implements Printer {
private StackSampler mStackSampler;
private boolean mPrintingStarted = false;
private long mStartTimestamp; // 卡顿阈值
private long mBlockThresholdMillis = 3000; //采样频率
private long mSampleInterval = 1000;
private Handler mLogHandler;
public MyPrinter() {
mStackSampler = new StackSampler(mSampleInterval);
HandlerThread handlerThread = new HandlerThread("block-canary-io");
handlerThread.start();
mLogHandler = new Handler(handlerThread.getLooper());
}
@Override
public void println(String x) {
//从if到else会执行 dispatchMessage，如果执行耗时超过阈值，输出卡顿信息
if (!mPrintingStarted) { //记录开始时间
mStartTimestamp = System.currentTimeMillis();
mPrintingStarted = true;
mStackSampler.startDump();
} else {
final long endTime = System.currentTimeMillis();
mPrintingStarted = false; //出现卡顿
if (isBlock(endTime)) {
notifyBlockEvent(endTime);
}
mStackSampler.stopDump();
}
}
private void notifyBlockEvent(final long endTime) {
mLogHandler.post(new Runnable() {
@Override
public void run() { //获得卡顿时 主线程堆栈
List stacks = mStackSampler.getStacks(mStartTimestamp, endTime);
for (String stack : stacks) {
Log.e("block-canary", stack);
}
}
});
}
private boolean isBlock(long endTime) {
return endTime - mStartTimestamp > mBlockThresholdMillis;
}
}
public class StackSampler {
public static final String SEPARATOR = "\r\n";
public static final SimpleDateFormat TIME_FORMATTER = new SimpleDateFormat("MM-dd HH:mm:ss.SSS");
private Handler mHandler;
private Map mStackMap = new LinkedHashMap<>();
private int mMaxCount = 100;
private long mSampleInterval; //是否需要采样
protected AtomicBoolean mShouldSample = new AtomicBoolean(false);
public StackSampler(long sampleInterval) {
mSampleInterval = sampleInterval;
HandlerThread handlerThread = new HandlerThread("block-canary-sampler");
handlerThread.start();
mHandler = new Handler(handlerThread.getLooper());
}
/*** 开始采样 执行堆栈 */
public void startDump() { //避免重复开始
if (mShouldSample.get()) {
return;
}
mShouldSample.set(true);
mHandler.removeCallbacks(mRunnable);
mHandler.postDelayed(mRunnable, mSampleInterval);
}
public void stopDump() {
if (!mShouldSample.get()) {
return;
}
mShouldSample.set(false);
mHandler.removeCallbacks(mRunnable);
}
public List getStacks(long startTime, long endTime) {
ArrayList result = new ArrayList<>();
synchronized (mStackMap) {
for (Long entryTime : mStackMap.keySet()) {
if (startTime < entryTime && entryTime < endTime) {
result.add(TIME_FORMATTER.format(entryTime) + SEPARATOR + SEPARATOR + mStackMap.get(entryTime));
}
}
}
return result;
}
private Runnable mRunnable = new Runnable() {
@Override
public void run() {
StringBuilder sb = new StringBuilder();
StackTraceElement[] stackTrace = Looper.getMainLooper().getThread().getStackTrace();
for (StackTraceElement s : stackTrace) {
sb.append(s.toString()).append("\n");
}
synchronized (mStackMap) { //最多保存100条堆栈信息
if (mStackMap.size() == mMaxCount) {
mStackMap.remove(mStackMap.keySet().iterator().next());
}
mStackMap.put(System.currentTimeMillis(), sb.toString());
}
if (mShouldSample.get()) {
mHandler.postDelayed(mRunnable, mSampleInterval);
}
}
};
}

二、使用Choreographer.FrameCallback

Android系统每隔16ms发出VSYNC信号，来通知界面进行重绘、渲染，每一次同步的周期约为16.6ms，代表一帧的刷新频率。通过Choreographer类设置它的FrameCallback函数，当每一帧被渲染时会触发回调FrameCallback.doFrame (long frameTimeNanos) 函数。frameTimeNanos是底层VSYNC信号到达的时间戳 。

通过 ChoreographerHelper 可以实时计算帧率和掉帧数，实时监测App页面的帧率数据，发现帧率过低，还可以自动保存现场堆栈信息。

public class ChoreographerHelper {
private static final String TAG = "ChoreographerHelper";
public static void start() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
Choreographer.getInstance().postFrameCallback(new Choreographer.FrameCallback() {
long lastFrameTimeNanos = 0;
@Override
public void doFrame(long frameTimeNanos) {
//上次回调时间
if (lastFrameTimeNanos == 0) {
lastFrameTimeNanos = frameTimeNanos;
Choreographer.getInstance().postFrameCallback(this);
return;
}
long diff = (frameTimeNanos - lastFrameTimeNanos) / 1_000_000;
if (diff > 16.6f) {
//掉帧数
int droppedFrameCount = (int) (diff / 16.6);
Log.d(TAG, "doFrame: droppedFrameCount=" + droppedFrameCount);
}
lastFrameTimeNanos = frameTimeNanos;
Choreographer.getInstance().postFrameCallback(this);
}
});
}
}
}