new IntentFilter(REBOOT_ACTION));
... // 系统启动时间 mBootTime = System.currentTimeMillis(); } ok,调用init函数启动完毕 2、运行中 run @ SysemServer.java 调用 Watchdog.getInstance().start(); 启动看门狗 首先看下 Watchdog 类定义：/** This class calls its monitor every minute. Killing this process if they don't return **/ public class Watchdog extends Thread { } 从线程类中继承，即会在一个单独线程中运行，调用thrrad.start()即调用 Watchdog.java 中的 run() 函数 public void run() { boolean waitedHalf = false; while (true) { mCompleted = false; // 1、给mHandler发送 MONITOR 消息，用于请求检查 Service是否工作正常 mHandler.sendEmptyMessage(MONITOR); synchronized (this) { // 2、进行 wait 等待 timeout 时间确认是否退出循环 long timeout = TIME_TO_WAIT; // NOTE: We use uptimeMillis() here because we do not want to increment the time we // wait while asleep. If the device is asleep then the thing that we are waiting // to timeout on is asleep as well and won't have a chance to run, causing a false // positive on when to kill things. long start = SystemClock.uptimeMillis(); while (timeout > 0 && !mForceKillSystem) { try { wait(timeout); // notifyAll() is called when mForceKillSystem is set } catch (InterruptedException e) { Log.wtf(TAG, e); } timeout = TIME_TO_WAIT - (SystemClock.uptimeMillis() - start); } // 3、如果 mCompleted 为真表示service一切正常，后面会再讲到 if (mCompleted && !mForceKillSystem) { // The monitors have returned. waitedHalf = false; continue; } // 4、表明检测到了有 deadlock-detection 条件发生，利用 dumpStackTraces 打印堆栈依信息 if (!waitedHalf) { // We've waited half the deadlock-detection interval. Pull a stack // trace and wait another half. ArrayList<Integer> pids = new ArrayList<Integer>(); pids.add(Process.myPid()); ActivityManagerService.dumpStackTraces(true, pids, null, null); waitedHalf = true; continue; // 不过这里会再次检测一次 } } SystemClock.sleep(2000); // 5、打印内核栈调用关系 // Pull our own kernel thread stacks as well if we're configured for that if (RECORD_KERNEL_THREADS) { dumpKernelStackTraces(); } // 6、ok,系统出问题了，检测到某个 Service 出现死锁情况，杀死SystemServer进程 // Only kill the process if the debugger is not attached. if (!Debug.isDebuggerConnected()) { Slog.w(TAG, "*** WATCHDOG KILLING SYSTEM PROCESS: " + name); Process.killProcess(Process.myPid()); System.exit(10); } else { Slog.w(TAG, "Debugger connected: Watchdog is *not* killing the system process"); } waitedHalf = false; } }主要工作逻辑：监控线程每隔一段时间发送一条 MONITOR 线另外一个线程，另个一个线程会检查各个 Service 是否正常运行，看门狗就不停的检查并等待结果，失败则杀死SystemServer. 3、Service 检查线程 /** * Used for scheduling monitor callbacks and checking memory usage. */ final class HeartbeatHandler extends Handler {@Override public void handleMessage(Message msg) { // Looper 消息处理函数 switch (msg.what) { case MONITOR: {
// 依次检测各个服务，即调用 monitor() 函数
final int size = mMonitors.size();
for (int i = 0 ; i < size ; i++) { mCurrentMonitor = mMonitors.get(i); mCurrentMonitor.monitor(); } // 检测成功则设置 mCompleted 变量为 true synchronized (Watchdog.this) { mCompleted = true; mCurrentMonitor = null; }下面我们来看一下各个Service如何确定自已运行ok呢？以 ActivityManagerService 为例：首先加入检查队列：private ActivityManagerService() { // Add ourself to the Watchdog monitors. Watchdog.getInstance().addMonitor(this); }然后实现 monitor() 函数： /** In this method we try to acquire our lock to make sure that we have not deadlocked */ public void monitor() { synchronized (this) { } } 明白了吧，其实就是检查这个 Service 是否发生了死锁，对于此情况就只能kill SystemServer系统了。对于死锁的产生原因非常多，但有个情况需要注意：java层死锁可能发生在调用native函数，而native函数可能与硬件交互导致时间过长而没有返回，从而导致长时间占用导致问题。 4、内存使用检测 消息发送 final class GlobalPssCollected implements Runnable { public void run() { mHandler.sendEmptyMessage(GLOBAL_PSS); } } 检测内存处理函数： final class HeartbeatHandler extends Handler { @Override public void handleMessage(Message msg) { switch (msg.what) { case GLOBAL_PSS: { if (mHaveGlobalPss) { // During the last pass we collected pss information, so // now it is time to report it. mHaveGlobalPss = false; if (localLOGV) Slog.v(TAG, "Received global pss, logging."); logGlobalMemory(); } } break; 其主要功能如下,统计pSS状况及读取相关linux内核中内存信息： void logGlobalMemory() { mActivity.collectPss(stats); Process.readProcLines("/proc/meminfo", mMemInfoFields, mMemInfoSizes); Process.readProcLines("/proc/vmstat", mVMStatFields, mVMStatSizes);}
转载于:https://www.cnblogs.com/dongdong230/p/4183081.html
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