参考
自动化卡顿检测方案及优化
深入探索Android卡顿优化（上）
深入探索Android卡顿优化（下）
卡顿
关于什么是卡顿？可以参考什么是卡顿
原理
在线监测
利用loop()中打印的日志
大家都知道在Android UI线程中有个Looper，在其loop方法中会不断取出Message，调用其绑定的Handler在UI线程进行执行。
大致代码如下：
public static void loop() {
final Looper me = myLooper();
final MessageQueue queue = me.mQueue;
// ...
for (;;) {
Message msg = queue.next(); // might block
// This must be in a local variable, in case a UI event sets the logger
Printer logging = me.mLogging;
if (logging != null) {
logging.println(">>>>> Dispatching to " + msg.target + " " +
msg.callback + ": " + msg.what);
}
// focus
msg.target.dispatchMessage(msg);
if (logging != null) {
logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);
}
// ...
}
msg.recycleUnchecked();
}
}第15行代码，就是有可能发生卡顿的地方，注意这行代码的前后，有两个logging。如果设置了logging，会分别打印出“>>>>> Dispatching to”和“<<<<< Finished to”这样的Log。这样就给我们监视两次Log之间的时间差，来判断是否发生了卡顿。
public final class Looper {
private Printer mLogging;
public void setMessageLogging(@Nullable Printer printer) {
mLogging = printer;
}
}
public interface Printer {
void println(String x);
}所以，我们可以自己实现一个Printer，在通过setMessageLogging()方法传入即可。
public class MyApplication extends Application {
@Override
public void onCreate() {
super.onCreate();
Looper.getMainLooper().setMessageLogging(new Printer() {
private static final String START = ">>>>> Dispatching";
private static final String END = "<<<<< Finished";
@Override
public void println(String x) {
if (x.startsWith(START)) {
LogMonitor.getInstance().startMonitor();
}
if (x.startsWith(END)) {
LogMonitor.getInstance().removeMonitor();
}
}
});
}
}LogMonitor的代码如下：
public class LogMonitor {
private static final long TIME_BLOCK = 1000L;
private static LogMonitor sInstance = new LogMonitor();
private HandlerThread mHandlerThread = new HandlerThread("log");
private Handler mHandler;
private LogMonitor() {
mHandlerThread.start();
mHandler = new Handler(mHandlerThread.getLooper());
}
private static 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() + "\n");
}
Log.e("TAG", sb.toString());
}
};
public static LogMonitor getInstance() {
return sInstance;
}
public void startMonitor() {
mHandler.postDelayed(mRunnable, TIME_BLOCK);
}
public boolean isMonitor() {
return mHandler.hasCallbacks(mRunnable);
}
public void removeMonitor() {
mHandler.removeCallbacks(mRunnable);
}
}BlockCanary就是基于这个原理实现的。
利用Choreographer
Android性能优化第（十 一）篇---卡顿分析，正确评测流畅度
有的时候会看到这样的log，系统帮助我们打印出了跳帧数：
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.这个log就出自于Choreographer中
public final class Choreographer {
void doFrame(long frameTimeNanos, int frame) {
final long startNanos;
synchronized (mLock) {
if (!mFrameScheduled) {
return; // no work to do
}
//当前时间
startNanos = System.nanoTime();
//抖动间隔
final long jitterNanos = startNanos - frameTimeNanos;
//抖动间隔大于屏幕刷新时间间隔（16ms）
if (jitterNanos >= mFrameIntervalNanos) {
final long skippedFrames = jitterNanos / mFrameIntervalNanos;
//跳过了几帧！，也许当前应用在主线程做了太多的事情。
if (skippedFrames >= SKIPPED_FRAME_WARNING_LIMIT) {
Log.i(TAG, "Skipped " + skippedFrames + " frames! "
+ "The application may be doing too much work on its main thread.");
}
//最后一次的屏幕刷是lastFrameOffset之前开始的
final long lastFrameOffset = jitterNanos % mFrameIntervalNanos;
if (DEBUG) {
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.");
}
//最后一帧的刷新开始时间
frameTimeNanos = startNanos - lastFrameOffset;
}
//由于跳帧可能造成了当前展现的是之前的帧，这样需要等待下一个vsync信号
if (frameTimeNanos < mLastFrameTimeNanos) {
if (DEBUG) {
Log.d(TAG, "Frame time appears to be going backwards. May be due to a "
+ "previously skipped frame. Waiting for next vsync.");
}
scheduleVsyncLocked();
return;
}
//当前画面刷新的状态置false
mFrameScheduled = false;
//更新最后一帧的刷新时间
mLastFrameTimeNanos = frameTimeNanos;
}
//按照优先级策略进行画面刷新时间处理
doCallbacks(Choreographer.CALLBACK_INPUT, frameTimeNanos);
doCallbacks(Choreographer.CALLBACK_ANIMATION, frameTimeNanos);
doCallbacks(Choreographer.CALLBACK_TRAVERSAL, frameTimeNanos);
if (DEBUG) {
final long endNanos = System.nanoTime();
Log.d(TAG, "Frame " + frame + ": Finished, took "
+ (endNanos - startNanos) * 0.000001f + " ms, latency "
+ (startNanos - frameTimeNanos) * 0.000001f + " ms.");
}
}
}当跳帧数大于设置的SKIPPED_FRAME_WARNING_LIMIT 值时会在当前进程输出这个log。由于 SKIPPED_FRAME_WARNING_LIMIT 的值默认为 30，所以上面的log并不是经常看到。
方法一
如果我们用反射的方法把SKIPPED_FRAME_WARNING_LIMIT的值设置成1，这样可以保证只要有丢帧，就会有上面的log输出来。
static {
try {
Field field = Choreographer.class.getDeclaredField("SKIPPED_FRAME_WARNING_LIMIT");
field.setAccessible(true);
field.set(Choreographer.class, 1);
} catch (Throwable e) {
e.printStackTrace();
}
}只要捕获这个log提取出skippedFrames 就可以知道界面是否卡顿。
方法二
上面的方法只能让我们知道丢帧了，却无法知道更详细定位问题的信息了。
在Choreographer中有个回调接口，FrameCallback。
public interface FrameCallback {
//当新的一帧被绘制的时候被调用。
public void doFrame(long frameTimeNanos);
}public class BlockDetectByChoreographer {
public static void start() {
Choreographer.getInstance()
.postFrameCallback(new Choreographer.FrameCallback() {
@Override
public void doFrame(long l) {
if (LogMonitor.getInstance().isMonitor()) {
LogMonitor.getInstance().removeMonitor();
}
LogMonitor.getInstance().startMonitor();
Choreographer.getInstance().postFrameCallback(this);
}
});
}
}第一次的时候开始检测，如果大于阈值则输出相关堆栈信息，否则则移除。
文章来源：Android异常处理之卡顿 - 作业部落 Cmd Markdown 编辑阅读器
