KOOM 浅析

class MonitorRunnable implements Runnable {
    ...
    @Override
    public void run() {
      if (stop) {
        return;
      }
      // 是否触发检测
      if (monitor.isTrigger()) {
        // 检测回调触发
        stop = monitorTriggerListener
            .onTrigger(monitor.monitorType(), monitor.getTriggerReason());
      }
      if (!stop) {
        // 间隔 5s 轮训检测
        handler.postDelayed(this, monitor.pollInterval());
      }
    }
  }
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@Override
  public boolean isTrigger() {
    ...
  // ①、获取当前的内存状态
    HeapStatus heapStatus = currentHeapStatus();
  // ②、当前使用内存是否达到最大阈值，内存使用占比超过 95%
    if (heapStatus.isOverMaxThreshold) {
      // 已达到最大阀值，强制触发 trigger，防止后续出现大内存分配导致 OOM 进程 Crash，无法触发 trigger
      currentTimes = 0;
      return true;
    }
  // ③、当前使用内存是否达到触发条件，内存使用占比超过 80、85、90
    if (heapStatus.isOverThreshold) {
      // 默认是 true
      if (heapThreshold.ascending()) {
         // ④、此时记录的内存占用比上次记录的高、达到最大阈值
        if (lastHeapStatus == null || heapStatus.used >= lastHeapStatus.used || heapStatus.isOverMaxThreshold) {
          currentTimes++;
        } else {
          currentTimes = 0;
        }
      } else {
        currentTimes++;
      }
    } else {
      currentTimes = 0;
    }
    // 将本地记录进行缓存
    lastHeapStatus = heapStatus;
    // ⑤、记录的次数超过 3 次，则触发条件
    return currentTimes >= heapThreshold.overTimes();
  }
  private HeapStatus lastHeapStatus;
  private HeapStatus currentHeapStatus() {
    HeapStatus heapStatus = new HeapStatus();
    heapStatus.max = Runtime.getRuntime().maxMemory();
    heapStatus.used = Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory();
    float heapInPercent = 100.0f * heapStatus.used / heapStatus.max;
    heapStatus.isOverThreshold = heapInPercent > heapThreshold.value();
    heapStatus.isOverMaxThreshold = heapInPercent > heapThreshold.maxValue();
    return heapStatus;
  }
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public void doHeapDump(TriggerReason.DumpReason reason) {
    // 生成 dump 的 hprof 文件存储路径
    KHeapFile.getKHeapFile().buildFiles();
    ...
    // 开始 dump
    boolean res = heapDumper.dump(KHeapFile.getKHeapFile().hprof.path);
    ...
  }
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@Override
  public boolean dump(String path) {
    ...
    // 适配 Android 11 ，和下面流程差不多
    if (Build.VERSION.SDK_INT > Build.VERSION_CODES.Q) {
      return dumpHprofDataNative(path);
    }
    ...
    try {
      // ①、挂起主进程并 for 出子进程
      int pid = trySuspendVMThenFork();
      if (pid == 0) {
        // ②、子进程开始 dump hprof
        Debug.dumpHprofData(path);
        // 结束子进程
        exitProcess();
      } else {
        // ③、恢复挂起的主进程
        resumeVM();
        // ④、等待子进程的 dump
        dumpRes = waitDumping(pid);
      }
    } catch (IOException e) {
       e.printStackTrace();
    }
    return dumpRes;
  }
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public boolean analyze() {
    // 查找泄漏的引用链
    Pair<List<ApplicationLeak>, List<LibraryLeak>> leaks = leaksFinder.find();
    if (leaks == null) {
      return false;
    }
    //将 gc 引用链写入到 report 文件中
    HeapAnalyzeReporter.addGCPath(leaks, leaksFinder.leakReasonTable);
    // 标记当前 report 已完成
    HeapAnalyzeReporter.done();
    return true;
  }
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