LeakCanary 内存泄露监测原理研究

"Read the fucking source code" -- linus一句名言体现出了阅读源码的重要性，学习别人得代码是提升自己的重要途径。最近用到了LeakCanary，顺便看一下其代码，学习一下。
LeakCanary是安卓中用来检测内存泄露的小工具，它能帮助我们提早发现代码中隐藏的bug, 降低应用中内存泄露以及OOM产生的概率。

废话不多说，关于LeakCanary的使用方法，其实很简单，如果我们只想检测Activity的内存泄露，而且只想使用其默认的报告方式，我们只需要在Application中加一行代码，

LeakCanary.install(this);

那我们今天阅读源码的切入点，就从这个静态方法开始。

 /**
   * Creates a {@link RefWatcher} that works out of the box, and starts watching activity
   * references (on ICS+).
   */
  public static RefWatcher install(Application application) {
    return install(application, DisplayLeakService.class,
        AndroidExcludedRefs.createAppDefaults().build());
  }

这个函数内部直接调用了另外一个重载的函数

/**
   * Creates a {@link RefWatcher} that reports results to the provided service, and starts watching
   * activity references (on ICS+).
   */
  public static RefWatcher install(Application application,
      Class listenerServiceClass,
      ExcludedRefs excludedRefs) {
    //判断是否在Analyzer进程里
    if (isInAnalyzerProcess(application)) {
      return RefWatcher.DISABLED;
    }
    enableDisplayLeakActivity(application);
    HeapDump.Listener heapDumpListener =
        new ServiceHeapDumpListener(application, listenerServiceClass);
    RefWatcher refWatcher = androidWatcher(application, heapDumpListener, excludedRefs);
    ActivityRefWatcher.installOnIcsPlus(application, refWatcher);
    return refWatcher;
  }

因为leakcanay会开启一个远程service用来分析每次产生的内存泄露，而安卓的应用每次开启进程都会调用Applicaiton的onCreate方法，因此我们有必要预先判断此次Application启动是不是在analyze service启动时，

public static boolean isInServiceProcess(Context context, Class serviceClass) {
    PackageManager packageManager = context.getPackageManager();
    PackageInfo packageInfo;
    try {
      packageInfo = packageManager.getPackageInfo(context.getPackageName(), GET_SERVICES);
    } catch (Exception e) {
      Log.e("AndroidUtils", "Could not get package info for " + context.getPackageName(), e);
      return false;
    }
    String mainProcess = packageInfo.applicationInfo.processName;

    ComponentName component = new ComponentName(context, serviceClass);
    ServiceInfo serviceInfo;
    try {
      serviceInfo = packageManager.getServiceInfo(component, 0);
    } catch (PackageManager.NameNotFoundException ignored) {
      // Service is disabled.
      return false;
    }

    if (serviceInfo.processName.equals(mainProcess)) {
      Log.e("AndroidUtils",
          "Did not expect service " + serviceClass + " to run in main process " + mainProcess);
      // Technically we are in the service process, but we're not in the service dedicated process.
      return false;
    }

    //查找当前进程名
    int myPid = android.os.Process.myPid();
    ActivityManager activityManager =
        (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
    ActivityManager.RunningAppProcessInfo myProcess = null;
    for (ActivityManager.RunningAppProcessInfo process : activityManager.getRunningAppProcesses()) {
      if (process.pid == myPid) {
        myProcess = process;
        break;
      }
    }
    if (myProcess == null) {
      Log.e("AndroidUtils", "Could not find running process for " + myPid);
      return false;
    }

    return myProcess.processName.equals(serviceInfo.processName);
  }

判断Application是否是在service进程里面启动，最直接的方法就是判断当前进程名和service所属的进程是否相同。当前进程名的获取方式是使用ActivityManager的getRunningAppProcessInfo方法，找到进程pid与当前进程pid相同的进程，然后从中拿到processName. service所属进程名。获取service应处进程的方法是用PackageManager的getPackageInfo方法。

RefWatcher

ReftWatcher是leakcancay检测内存泄露的发起点。使用方法为，在对象生命周期即将结束的时候，调用

RefWatcher.watch(Object object)

为了达到检测内存泄露的目的，RefWatcher需要

  private final Executor watchExecutor;
  private final DebuggerControl debuggerControl;
  private final GcTrigger gcTrigger;
  private final HeapDumper heapDumper;
  private final Set retainedKeys;
  private final ReferenceQueue