如何监控项目里所有UI线程的操作（实战，BlockCanary）？
如何监控项目里所有UI线程的操作（实战，BlockCanary）？
背景
我们都知道，Android系统是线程安全的，也就是只有主线才能更新UI。而保持界面的流畅性，就要求界面1秒钟刷新60次以上。也就是16ms需要刷新一次界面。但是在实际开发过程中，有各种各样的原因，无法达到这一指标。尤其是当项目已经成形，需求的不断变更，开发人员的变更、替换，等等，就变成的更为困难。寻找这些影响主线程执行效率的代码，就变成一个优化性能的重要方面。在学习前人的优秀的设计思想和代码实现，下面带着大家一步一步地实战。
原理
先说一下原理，我们都知道，Android是使用Message/Looper/Handler机制来更新UI的。如果在主线程handler的handleMessage方法进行了耗时的操作，界面也就是不能及时更新，即UI卡顿。关键代码如下：
Handler.dispatchMessage()方法
/** * Handle system messages here. */
public void dispatchMessage(Message msg) {
if (msg.callback != null) {
handleCallback(msg);
} else {
if (mCallback != null) {
if (mCallback.handleMessage(msg)) {
return;
}
}
handleMessage(msg);
}
}在来看一下Handler.dispatchMessage是在哪里被调用的，通过查看源码原来是在Looper.loop里调用，这里处主线程理消息队列的Looper。一个线程只有一个Looper,每一个消息都可以持有不同的Handler。也就是，所有的消息都会在这里进行处理和分发。所以只有监控此处就可以了。
Looper.loop()方法
/** * Run the message queue in this thread. Be sure to call * {@link #quit()} to end the loop. */
public static void loop() {
final Looper me = myLooper();
if (me == null) {
throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");
}
final MessageQueue queue = me.mQueue;
// Make sure the identity of this thread is that of the local process,
// and keep track of what that identity token actually is.
Binder.clearCallingIdentity();
final long ident = Binder.clearCallingIdentity();
for (;;) {
Message msg = queue.next(); // might block
if (msg == null) {
// No message indicates that the message queue is quitting.
return;
}
// 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);
}
msg.target.dispatchMessage(msg);
if (logging != null) {
logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);
}
// Make sure that during the course of dispatching the
// identity of the thread wasn't corrupted.
final long newIdent = Binder.clearCallingIdentity();
if (ident != newIdent) {
Log.wtf(TAG, "Thread identity changed from 0x"
+ Long.toHexString(ident) + " to 0x"
+ Long.toHexString(newIdent) + " while dispatching to "
+ msg.target.getClass().getName() + " "
+ msg.callback + " what=" + msg.what);
}
msg.recycleUnchecked();
}
}找到dispatchMessage的关键代码，即两个logging之间就是又可以出现耗时操作的地方。
// 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);
}
msg.target.dispatchMessage(msg);
if (logging != null) {
logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);
}你可能要问了，mLogging是什么，我可以打印出来吗？答案：是可以的，不信可以看下源码
public final class Looper {
private Printer mLogging;
/** * Control logging of messages as they are processed by this Looper. If * enabled, a log message will be written to <var>printer</var> * at the beginning and ending of each message dispatch, identifying the * target Handler and message contents. * * @param printer A Printer object that will receive log messages, or * null to disable message logging. */
public void setMessageLogging(@Nullable Printer printer) {
mLogging = printer;
}
}
/** * Simple interface for printing text, allowing redirection to various * targets. Standard implementations are {@link android.util.LogPrinter}, * {@link android.util.StringBuilderPrinter}, and * {@link android.util.PrintWriterPrinter}. */
public interface Printer {
/** * Write a line of text to the output. There is no need to terminate * the given string with a newline. */
void println(String x);
}Looper的mLogging居然是个私有的，而Printer还是接口(默认是没有打印的)，不过没有关系Looper提供了
setMessageLogging(@Nullable Printer printer)的公开方法，在自己实现一个Printer，传进出就好了。
1.编写能监控更新UI的代码
好吧，你已经知道，怎么做了。直接粘代码了。
/** * Created by zhangls on 2016/7/6. */
public class AppContext extends Application {
@Override
public void onCreate() {
super.onCreate();
Looper.getMainLooper().setMessageLogging(new Printer() {
@Override
public void println(String x) {
Log.e("AppContext", x);
}
});
}
}打印的log如下：
E/AppContext: <<<<< Finished to Handler (android.app.ActivityThread$H) {414a36b0} null
E/AppContext: >>>>> Dispatching to Handler (android.view.ViewRootImpl) {41d5dbd8} null: 1000
E/AppContext: <<<<< Finished to Handler (android.view.ViewRootImpl) {41d5dbd8} null
E/AppContext: >>>>> Dispatching to Handler (android.view.ViewRootImpl) {41d5dbd8} 2.找出过滤出耗时操作的Log
这个也不复杂，不多说了，看了代码，你就懂了。
/** * Created by zhangls on 2016/7/6. */
public class AppContext extends Application {
@Override
public void onCreate() {
super.onCreate();
Looper.getMainLooper().setMessageLogging(new MyPrinter());
}
private static class MyPrinter implements Printer {
public static final String TAG = "Printer";
private long mFinishTimeMillis;
private long mStartTimeMillis;
private static final int START = 0;
private static final int FINISH = 1;
private static final int UNKONW = 2;
@Override
public void println(String x) {
switch (isStart(x)) {
case START:
mStartTimeMillis = System.currentTimeMillis();
break;
case FINISH:
mFinishTimeMillis = System.currentTimeMillis();
long duration = mFinishTimeMillis - mStartTimeMillis;
if (isBlock(duration)) {
Log.e(TAG, "block time:" + duration);
}
break;
}
}
public int isStart(String x) {
if (!TextUtils.isEmpty(x)) {
if (x.startsWith(">>>>> Dispatching to Handler")) {
return START;
} else if (x.startsWith("<<<<< Finished to Handler")) {
return FINISH;
}
}
return UNKONW;
}
private boolean isBlock(long duration) {
return duration > 16;
}
}
}3.保存主线程所有的堆栈信息
先说下如何获取主线程的堆栈信息
StackTraceElement[] stackTrace = Looper.getMainLooper().getThread().getStackTrace();
由于这个代码是反射也是一个耗时操作，所以不得不专门写一个Thread来不断获取主线程的堆栈信息。
public class StackInfoCatcher extends Thread {
private static final String TAG = "StackInfoCatcher";
private static final int SIZE = 1024;
private boolean stop = false;
private long mLastTime = 0;
private List<StackTraceInfo> mList = new ArrayList<>(SIZE);
@Override
public void run() {
super.run();
while (!stop) {
long currentTime = System.currentTimeMillis();
if ((currentTime - mLastTime) > 500) {
mLastTime = System.currentTimeMillis();
StackTraceInfo info = new StackTraceInfo();
info.mTime = mLastTime;
StackTraceElement[] stackTrace = Looper.getMainLooper().getThread().getStackTrace();
info.mLog = stackTraceToString(stackTrace);
mList.add(info);
}
if (mList.size() > SIZE) {
mList.remove(0);
}
}
}
public String stackTraceToString(StackTraceElement[] elements) {
StringBuilder result = new StringBuilder();
if (null != elements && elements.length > 0) {
for (int i = 0; i < elements.length; i++) {
result.append("\tat ");
result.append(elements[i].toString());
result.append("\n");
}
}
return result.toString();
}
public void stopTrace() {
stop = true;
}
private class StackTraceInfo {
public long mTime;
public String mLog;
}
}4.获取耗时操作对应的堆栈信息
当主线程遇到耗时操作，则发送广播交由工作线程处理。并把开始时间和结束时间也发送过去。寻找这个时间段主线程产生的LOG和堆栈信息。
class MyPrinter implements Printer {
private MyPrinter(Context context) {
this.mContext = context;
stackInfoCatcher = new StackInfoCatcher(context);
stackInfoCatcher.start();
}
@Override
public void println(String x) {
switch (isStart(x)) {
case START:
mStartTimeMillis = System.currentTimeMillis();
break;
case FINISH:
mFinishTimeMillis = System.currentTimeMillis();
long duration = mFinishTimeMillis - mStartTimeMillis;
if (isBlock(duration)) {
LocalBroadcastManager manager= LocalBroadcastManager.getInstance(mContext);
Intent intent = new Intent("ACTION_BLOCK");
intent.putExtra("start", mStartTimeMillis);
intent.putExtra("finish", mFinishTimeMillis);
manager.sendBroadcast(intent);
}
break;
}
}
}public class StackInfoCatcher extends Thread {
public StackInfoCatcher(Context context) {
this.mContext = context;
LocalBroadcastManager manager = LocalBroadcastManager.getInstance(context);
mBroadcastReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
long endTime = intent.getLongExtra("finish", 0);
long startTime = intent.getLongExtra("start", 0);
StackTraceInfo info = getInfoByTime(endTime, startTime);
if (null != info) {
Log.e(TAG, "find block line" + (endTime - startTime));
Log.e(TAG, info.mLog);
} else {
Log.e(TAG, "no block line find");
}
}
};
manager.registerReceiver(mBroadcastReceiver, new IntentFilter("ACTION_BLOCK"));
}
public StackTraceInfo getInfoByTime(long endTime, long startTime) {
for (StackTraceInfo info : mList) {
if (info.mTime >= startTime && info.mTime <= endTime) {
return info;
}
}
return null;
}
public void stopTrace() {
stop = true;
LocalBroadcastManager.getInstance(mContext).unregisterReceiver(mBroadcastReceiver);
}
}5.测试并验证
编写一个Button，点击这个按钮主线程睡眠500ms。
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void click(View view) {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}对应日志如下
E: no block line find
E: find block line526
E: at java.lang.VMThread.sleep(Native Method)
at java.lang.Thread.sleep(Thread.java:1031)
at java.lang.Thread.sleep(Thread.java:1013)
at com.example.zhangls.myapplication1.MainActivity.click(MainActivity.java:21)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:3511)
at android.view.View.onKeyUp(View.java:6073)
at android.widget.TextView.onKeyUp(TextView.java:5541)
at android.view.KeyEvent.dispatch(KeyEvent.java:3279)
at android.view.View.dispatchKeyEvent(View.java:5500)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1246)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1246)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1246)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1246)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1246)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1246)
at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchKeyEvent(PhoneWindow.java:1904)
at com.android.internal.policy.impl.PhoneWindow.superDispatchKeyEvent(PhoneWindow.java:1386)
at android.app.Activity.dispatchKeyEvent(Activity.java:2327)
at android.support.v7.app.AppCompatActivity.dispatchKeyEvent(AppCompatActivity.java:534)
at android.support.v7.view.WindowCallbackWrapper.dispatchKeyEvent(WindowCallbackWrapper.java:50)
at android.support.v7.app.AppCompatDelegateImplBase$AppCompatWindowCallbackBase.dispatchKeyEvent(AppCompatDelegateImplBase.java:241)
at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1831)
at android.view.ViewRootImpl.deliverKeyEventPostIme(ViewRootImpl.java:3327)
at android.view.ViewRootImpl.handleFinishedEvent(ViewRootImpl.java:3300)
at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2460)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4425)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:848)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:575)
at dalvik.system.NativeStart.main(Native Method)总结
在主线程寸土寸金的地方，这个种办法本身也是占用主线程的执行时间的，所以在打包release版本的时候，要记得把这个去掉。
参考
- http://blog.zhaiyifan.cn/2016/01/16/BlockCanaryTransparentPerformanceMonitor/
- https://github.com/fengcunhan/BlockCanary