Android BlockCanary源码解析

红太狼 2023-07-07 12:44 24阅读 0赞

BlockCanary是什么  
非侵入式的性能监控组件

BlockCanary的作用  
发现UI卡顿问题（平时ANR时候我们才能获取到当堆栈的信息）

UI卡顿原理  
1.60fps---->16m/s帧  
2.尽量保证每次在16m/s内处理完所有的CPU与GPU计算绘制，渲染等操作，否则就会造成丢帧卡顿问题

主线程的作用  
1.主线程的作用（应用启动后，创建一个主线程，就是ActivityThread）  
2.把事件（点击，触摸等）发给合适的View或者Widget  
3.同时也是应用与应用UI交互的主线程

耗时操作常见的在子线程处理的方法,（耗时操作不能在主线程处理）  
Handler  
Activity.runOnUiThread(Runnable)  
View.post(Runnable)  
View.postDelayed(Runnable,long)

UI卡顿的常见原因  
1.耗时操作  
2.布局Layout过于复杂，无法在16m/s内完成渲染  
3.View的过度绘制  
4.View频繁的触发measure，layout  
5.内存频繁触发GC过多（虚拟机在执行垃圾回收的时候，所有的线程，包括UI线程都会暂停，只有当GC垃圾回收完后，所有的线程才能继续执行工作）

先看下\[ActivityThread\]（Android应用程序只有一个主线程，就是ActivityThread）  
[看Android源码网站地址][Android]

//创建一个Looper,Looper里又会关联消息队列MessageQueue
       final Looper mLooper = Looper.myLooper();
        public static void main(String[] args) { 
                   .
                   .
                   .
        //一个主线程创建MainLooper后，就会在我们的应用生命周期内，不断轮询，通过Looper.loop()方法，获取到消息队列中的Message，然后通知我们的主线程，去更新UI
       Looper.prepareMainLooper();  
        }

看下prepareMainLooper()方法

public static void prepareMainLooper() { 
     prepare(false);
     synchronized (Looper.class) { 
       if (sMainLooper != null) { 
        throw new IllegalStateException("The main Looper has already been prepared.");
         }
         //创建一个主线程的Looper（不管整个应用的主线程，它有多少个子线程，主线程中只有这一个Looper，不管有多少Hanlder，在其它地方可以创建Handler，最终会会到这个sMainLooper 上）
         sMainLooper = myLooper();
       }
      }

[看下Looper.loop()方法][Looper.loop]

//在msg.target.dispatchMessage(msg)方法上下方都有log输出，在dispatchMessage上下分别打印方法执行的时间，根据时间差，来判定dispatchMessage中有没有耗时操作，也就是dispatchMessage中，有没有UI卡顿，如果超过时间差的阈值，就要打印出信息，BlockCanary就是利了这个特点，这也是它的核心实现原理
    public static void loop() { 
                 final Printer logging = me.mLogging;
                final long dispatchStart = needStartTime ? SystemClock.uptimeMillis() : 0;
                          final long dispatchEnd;
                           try { 
                           //分发message，target就是Handler
                               msg.target.dispatchMessage(msg);
                               dispatchEnd = needEndTime ? SystemClock.uptimeMillis() : 0;
                           } finally { 
                               if (traceTag != 0) { 
                                   Trace.traceEnd(traceTag);
                               }
                           }
                           if (logSlowDelivery) { 
                                  if (slowDeliveryDetected) { 
                                      if ((dispatchStart - msg.when) <= 10) { 
                                          Slog.w(TAG, "Drained");
                                          slowDeliveryDetected = false;
                                      }
                                  } else { 
                                      if (showSlowLog(slowDeliveryThresholdMs, msg.when, dispatchStart, "delivery",
                                              msg)) { 
                                          // Once we write a slow delivery log, suppress until the queue drains.
                                          slowDeliveryDetected = true;
                                     }
                                  }
                              }
                              if (logSlowDispatch) { 
                                  showSlowLog(slowDispatchThresholdMs, dispatchStart, dispatchEnd, "dispatch", msg);
                              }
                  
                           if (logging != null) { 
                               logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);        .
                      
    }

看下msg.target.dispatchMessage(msg)方法

//这都是执行在主线程中，如果产生了UI卡顿，必定是在这个方法当中
     public void dispatchMessage(Message msg) { 
     //callback就是runnable
      if (msg.callback != null) { 
      //handleCallback,就是把runnable放到方法中，调用它的run方法执行我们的子线程
       handleCallback(msg);
        } else { 
        //相当于调用hanlder.sendMessage
         if (mCallback != null) { 
             if (mCallback.handleMessage(msg)) { 
              return;
                }    
              }
              //处理消息
               handleMessage(msg);
             }
           }

看下BlockCanary.install方法

public static BlockCanary install(Context context, BlockCanaryContext blockCanaryContext) { 
        //init方法就做了BlockCanaryContext的成员变量的赋值
        BlockCanaryContext.init(context, blockCanaryContext);
        //设置通知栏消息是否开启或关闭，BlockCanaryContext.get().displayNotification()，debug模式默开启(true)，release默认关闭(false)
        setEnabled(context, DisplayActivity.class, BlockCanaryContext.get().displayNotification());
        return get();
    }

看下get()方法

public static BlockCanary get() { 
           //单例，生成BlockCanary的实例
            if (sInstance == null) { 
                synchronized (BlockCanary.class) { 
                    if (sInstance == null) { 
                        sInstance = new BlockCanary();
                    }
                }
            }
            return sInstance;
        }

看下BlockCanary构造方法

private BlockCanary() { 
            BlockCanaryInternals.setContext(BlockCanaryContext.get());
            //单例获取
            mBlockCanaryCore = BlockCanaryInternals.getInstance();
            mBlockCanaryCore.addBlockInterceptor(BlockCanaryContext.get());
            if (!BlockCanaryContext.get().displayNotification()) { 
                return;
            }
            //通知展示
            mBlockCanaryCore.addBlockInterceptor(new DisplayService());
    
        }

看下BlockCanaryInternals的构造方法

public BlockCanaryInternals() { 
             //dump出线程的stack信息，传入的参数是主线程,第二个参数是Dump的间隔 
            stackSampler = new StackSampler(
                    Looper.getMainLooper().getThread(),
                    sContext.provideDumpInterval());
            //dump出cpu的有关情况
            cpuSampler = new CpuSampler(sContext.provideDumpInterval());
           //LooperMonitor是在dispatchMessage上下分别打印方法执行的时间
            setMonitor(new LooperMonitor(new LooperMonitor.BlockListener() { 
                //主线程的调用栈，CPU的是使用情况，内存使用情况都会这个方法监听到，会回调
                @Override
                public void onBlockEvent(long realTimeStart, long realTimeEnd,
                                         long threadTimeStart, long threadTimeEnd) { 
                    // Get recent thread-stack entries and cpu usage
                    ArrayList<String> threadStackEntries = stackSampler
                            .getThreadStackEntries(realTimeStart, realTimeEnd);
                    if (!threadStackEntries.isEmpty()) { 
                        BlockInfo blockInfo = BlockInfo.newInstance()
                                .setMainThreadTimeCost(realTimeStart, realTimeEnd, threadTimeStart, threadTimeEnd)
                                .setCpuBusyFlag(cpuSampler.isCpuBusy(realTimeStart, realTimeEnd))
                                .setRecentCpuRate(cpuSampler.getCpuRateInfo())
                                .setThreadStackEntries(threadStackEntries)
                                .flushString();
                        LogWriter.save(blockInfo.toString());
    
                        if (mInterceptorChain.size() != 0) { 
                            for (BlockInterceptor interceptor : mInterceptorChain) { 
                                interceptor.onBlock(getContext().provideContext(), blockInfo);
                            }
                        }
                    }
                }
            }, getContext().provideBlockThreshold(), getContext().stopWhenDebugging()));
           //就是用来删除日志用的，因为在BlockCanary当中,默认情况下日志会保存两天，需要定期的删除 
            LogWriter.cleanObsolete();
        }

看下start() 方法

public void start() { 
            if (!mMonitorStarted) { 
                mMonitorStarted = true;
    // Looper.getMainLooper()得到主线程Looper，调用setMessageLogging打印时间 Looper.getMainLooper().setMessageLogging(mBlockCanaryCore.monitor);
            }
        }

看下LooperMonitor的println(String x)方法

//打印时间
      public void println(String x) { 
            if (mStopWhenDebugging && Debug.isDebuggerConnected()) { 
                return;
            }
            //表示是否在dispatchMessage方法前
            if (!mPrintingStarted) { 
              //系统时间
                mStartTimestamp = System.currentTimeMillis();
                //当前线程运行状态的总时间（sleep和wait不会记录到时间里去）
                mStartThreadTimestamp = SystemClock.currentThreadTimeMillis();
                mPrintingStarted = true;
                startDump();
            } else {   //表示是否在dispatchMessage方法后
                final long endTime = System.currentTimeMillis();
                mPrintingStarted = false;
                //表示有卡顿，UI有阻塞
                if (isBlock(endTime)) { 
                    notifyBlockEvent(endTime);
                }
                stopDump();
            }
        }

看下startDump()方法

private void startDump() { 
            if (null != BlockCanaryInternals.getInstance().stackSampler) { 
                BlockCanaryInternals.getInstance().stackSampler.start();
            }
    
            if (null != BlockCanaryInternals.getInstance().cpuSampler) { 
                BlockCanaryInternals.getInstance().cpuSampler.start();
            }
        }

看下BlockCanaryInternals.getInstance().stackSampler.start()方法

public void start() { 
            if (mShouldSample.get()) { 
                return;
            }
            mShouldSample.set(true);
    
            HandlerThreadFactory.getTimerThreadHandler().removeCallbacks(mRunnable);
            HandlerThreadFactory.getTimerThreadHandler().postDelayed(mRunnable,
                    BlockCanaryInternals.getInstance().getSampleDelay());
        }

看下mRunnable，在aabstract class AbstractSampler 里，AbstractSampler 是stackSampler和cpuSampler的抽象类

private Runnable mRunnable = new Runnable() { 
            @Override
            public void run() { 
                doSample();
    
                if (mShouldSample.get()) { 
                    HandlerThreadFactory.getTimerThreadHandler()
                            .postDelayed(mRunnable, mSampleInterval);
                }
            }
        };

看下 doSample()抽象方法StackSampler的实现

//打印栈的信息
    rotected void doSample() { 
            StringBuilder stringBuilder = new StringBuilder();
    //mCurrentThread.getStackTrace()获取到当前线程的调用栈，mCurrentThread是主线程，因为前面调用的是getMainLooper
            for (StackTraceElement stackTraceElement : mCurrentThread.getStackTrace()) { 
                stringBuilder
                        .append(stackTraceElement.toString())
                        .append(BlockInfo.SEPARATOR);
            }
    
            synchronized (sStackMap) { 
                if (sStackMap.size() == mMaxEntryCount && mMaxEntryCount > 0) { 
                    sStackMap.remove(sStackMap.keySet().iterator().next());
                }
                //以当前时间为Key，放入到HashMap中，sStackMap是LinkedHashMap，这里为什么要定义为LinkedHashMap,LinkedHashMap会记录插入的键的顺序，所以遍历的时候是按插入顺序的，普通的HashMap无法做到，所以遍历顺序未知
                sStackMap.put(System.currentTimeMillis(), stringBuilder.toString());
            }
        }

看下 doSample()抽象方法CpuSampler的实现

@Override
    protected void doSample() { 
        BufferedReader cpuReader = null;
        BufferedReader pidReader = null;
    
        try { 
           //就是读写
            cpuReader = new BufferedReader(new InputStreamReader(
                    new FileInputStream("/proc/stat")), BUFFER_SIZE);
            String cpuRate = cpuReader.readLine();
            if (cpuRate == null) { 
                cpuRate = "";
            }
                         .
                         .
                         .               
           
        } } catch (Throwable throwable) { }
        }

看下isBlock(endTime)方法

private boolean isBlock(long endTime) { 
      //endTime是dispatchMessage后的时间，mStartTimestamp 是dispatchMessage前的时间，mBlockThresholdMillis时间为3000，如果大于就表示产生卡顿了，UI阻塞了
            return endTime - mStartTimestamp > mBlockThresholdMillis;
        }

看下 notifyBlockEvent(endTime)方法

private void notifyBlockEvent(final long endTime) { 
            final long startTime = mStartTimestamp;
            final long startThreadTime = mStartThreadTimestamp;
            final long endThreadTime = SystemClock.currentThreadTimeMillis();
            HandlerThreadFactory.getWriteLogThreadHandler().post(new Runnable() { 
                @Override
                public void run() { 
                //调用前面所说的监听事件
                    mBlockListener.onBlockEvent(startTime, endTime, startThreadTime, endThreadTime);
                }
            });
        }

[Android]: http://androidxref.com
[Looper.loop]: http://androidxref.com/9.0.0_r3/xref/frameworks/base/core/java/android/os/Looper.java