PowerManagerService流程分析

Posted 2020-09-26

一、PowerManagerService简介

　　PowerManagerService主要服务android系统电源管理工作，这样讲比较笼统，就具体细节上大致可以认为PowerManagerService集中处理用户活动（如点击屏幕，按电源键等）、电量变化、用户设置（如在Setting中设置省电模式，飞行模式）、插拔充电器（无线冲，有线冲）等。当发生以上事件时，PowerManagerService都要进行各种状态的更新，以下把PMS作为PowerManagerService的简称

二、PowerManagerService启动流程

2.1、PMS启动

        // Power manager needs to be started early because other services need it.
        // Native daemons may be watching for it to be registered so it must be ready
        // to handle incoming binder calls immediately (including being able to verify
        // the permissions for those calls).
        mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
    .
    .
    .
        try {
            // TODO: use boot phase
            mPowerManagerService.systemReady(mActivityManagerService.getAppOpsService());
        } catch (Throwable e) {
            reportWtf("making Power Manager Service ready", e);
        }

 

2.2、SystemServiceManager.startService()

 

 1     public <T extends SystemService> T startService(Class<T> serviceClass) {
 2         final String name = serviceClass.getName();
 3         Slog.i(TAG, "Starting " + name);
 4 
 5         // Create the service.
 6         if (!SystemService.class.isAssignableFrom(serviceClass)) {
 7             throw new RuntimeException("Failed to create " + name
 8                     + ": service must extend " + SystemService.class.getName());
 9         }
10         final T service;
11         try {
12             Constructor<T> constructor = serviceClass.getConstructor(Context.class);
13             service = constructor.newInstance(mContext);
14         } catch (InstantiationException ex) {
15             throw new RuntimeException("Failed to create service " + name
16                     + ": service could not be instantiated", ex);
17         } catch (IllegalAccessException ex) {
18             throw new RuntimeException("Failed to create service " + name
19                     + ": service must have a public constructor with a Context argument", ex);
20         } catch (NoSuchMethodException ex) {
21             throw new RuntimeException("Failed to create service " + name
22                     + ": service must have a public constructor with a Context argument", ex);
23         } catch (InvocationTargetException ex) {
24             throw new RuntimeException("Failed to create service " + name
25                     + ": service constructor threw an exception", ex);
26         }
27 
28         // Register it.
29         mServices.add(service);
30 
31         // Start it.
32         try {
33             service.onStart();
34         } catch (RuntimeException ex) {
35             throw new RuntimeException("Failed to start service " + name
36                     + ": onStart threw an exception", ex);
37         }
38         return service;
39     }

 在Android5.0以后SystemServer启动服务的方式发生了改变，在Android4.4以前SystemServer通过new方法创建服务的对象，并把服务注册到SystemManager中；Android5.0以后SystemServer通过SystemServiceManager.startService来启动服务，主要通过反射的方式获取服务的构造方法，并创建服务对象；最后调用服务重写的onStart（）方法。

说明：Android5.0以后所有服务都实现SystemService接口，这样方法服务的统一管理。

2.3 、PMS构造方法

 

 public PowerManagerService(Context context) {
        super(context);
        mContext = context;
        //启动一个线程，创建一个handler，handler发送的消息由该线程来处理
        mHandlerThread = new ServiceThread(TAG,
                Process.THREAD_PRIORITY_DISPLAY, false /*allowIo*/);
        mHandlerThread.start();
        mHandler = new PowerManagerHandler(mHandlerThread.getLooper());

        synchronized (mLock) {
            //创建两个suspendBlocker对象，获取suspendblocker防止cpu进去休眠
            mWakeLockSuspendBlocker = createSuspendBlockerLocked("PowerManagerService.WakeLocks");
            mDisplaySuspendBlocker = createSuspendBlockerLocked("PowerManagerService.Display");
            mDisplaySuspendBlocker.acquire();
            mHoldingDisplaySuspendBlocker = true;
            mHalAutoSuspendModeEnabled = false;
            mHalInteractiveModeEnabled = true;

            mWakefulness = WAKEFULNESS_AWAKE;
            //初始化电源相关设置，这些方法通过jni调动native方法
            nativeInit();
            nativeSetAutoSuspend(false);
            nativeSetInteractive(true);
            nativeSetFeature(POWER_FEATURE_DOUBLE_TAP_TO_WAKE, 0);
        }
    }

 

2.4、OnStart()方法

 

 1     @Override
 2     public void onStart() {
 3         //BinderService继承IPowerManager.Stub，其实就是PowerManager的服务端
 4         //这里其实就是把BinderService对象注册到ServiceManager中
 5         publishBinderService(Context.POWER_SERVICE, new BinderService());
 6         publishLocalService(PowerManagerInternal.class, new LocalService());
 7 
 8         //加入Watchdog监听
 9         Watchdog.getInstance().addMonitor(this);
10         Watchdog.getInstance().addThread(mHandler);
11     }

 

2.5、systemReady()方法

    public void systemReady(IAppOpsService appOps) {
        synchronized (mLock) {
            mSystemReady = true;
            mAppOps = appOps;
            mDreamManager = getLocalService(DreamManagerInternal.class);
            mDisplayManagerInternal = getLocalService(DisplayManagerInternal.class);
            mPolicy = getLocalService(WindowManagerPolicy.class);
            mBatteryManagerInternal = getLocalService(BatteryManagerInternal.class);

            PowerManager pm = (PowerManager) mContext.getSystemService(Context.POWER_SERVICE);
            //最大、最小、默认的屏幕亮超时时间
            mScreenBrightnessSettingMinimum = pm.getMinimumScreenBrightnessSetting();
            mScreenBrightnessSettingMaximum = pm.getMaximumScreenBrightnessSetting();
            mScreenBrightnessSettingDefault = pm.getDefaultScreenBrightnessSetting();
            //传感器相关，传感器检查到外部事件可以通过发送消息到mHandler的消息队列中处理
            SensorManager sensorManager = new SystemSensorManager(mContext, mHandler.getLooper());

            // The notifier runs on the system server‘s main looper so as not to interfere
            // with the animations and other critical functions of the power manager.
            mBatteryStats = BatteryStatsService.getService();
            
            //注意上面的注释，notifier运行在system server的主线程中，并且参数中传入了一个SuspendBlocker对象，应该发送通知的时候需要点亮屏幕
            mNotifier = new Notifier(Looper.getMainLooper(), mContext, mBatteryStats,
                    mAppOps, createSuspendBlockerLocked("PowerManagerService.Broadcasts"),
                    mPolicy);
            //无线充电器相关，参数中传入了sensorManager，并且参数中传入了一个SuspendBlocker对象，也是为了有外部事件发生时点亮屏幕
            mWirelessChargerDetector = new WirelessChargerDetector(sensorManager,
                    createSuspendBlockerLocked("PowerManagerService.WirelessChargerDetector"),
                    mHandler);
            //ContentObserver对象，用来监听电源相关设置的改变
            mSettingsObserver = new SettingsObserver(mHandler);

            mLightsManager = getLocalService(LightsManager.class);
            mAttentionLight = mLightsManager.getLight(LightsManager.LIGHT_ID_ATTENTION);

            // Initialize display power management.
            mDisplayManagerInternal.initPowerManagement(
                    mDisplayPowerCallbacks, mHandler, sensorManager);

            // Register for broadcasts from other components of the system.

            //注册一些广播监听器，如电量变化、用户切换(多用户模式，一般手机就是单用户)
            IntentFilter filter = new IntentFilter();
            filter.addAction(Intent.ACTION_BATTERY_CHANGED);
            filter.setPriority(IntentFilter.SYSTEM_HIGH_PRIORITY);
            mContext.registerReceiver(new BatteryReceiver(), filter, null, mHandler);

            filter = new IntentFilter();
            filter.addAction(Intent.ACTION_DREAMING_STARTED);
            filter.addAction(Intent.ACTION_DREAMING_STOPPED);
            mContext.registerReceiver(new DreamReceiver(), filter, null, mHandler);

            filter = new IntentFilter();
            filter.addAction(Intent.ACTION_USER_SWITCHED);
            mContext.registerReceiver(new UserSwitchedReceiver(), filter, null, mHandler);

            filter = new IntentFilter();
            filter.addAction(Intent.ACTION_DOCK_EVENT);
            mContext.registerReceiver(new DockReceiver(), filter, null, mHandler);

            // Register for settings changes.
            //监听系统中对电源的设置，如开启省电模式、默认休眠超时时间、屏幕亮度、充电是否亮屏等等
            final ContentResolver resolver = mContext.getContentResolver();
            resolver.registerContentObserver(Settings.Secure.getUriFor(
                    Settings.Secure.SCREENSAVER_ENABLED),
                    false, mSettingsObserver, UserHandle.USER_ALL);
            .......
            .......
            .......
            // Go.
            //读取资源文件中电源相关设置
            readConfigurationLocked();
            //更新设置中对电源的相关设置
            updateSettingsLocked();
            mDirty |= DIRTY_BATTERY_STATE;
            //更新电源状态，这里统一处理了所有的状态更新，该方法会被频繁调用
            updatePowerStateLocked();
        }
    }

 

2.6、updatePowerStateLocked()方法

 

三、PowerManager用法

 

PowerManager的用法很简单，我们主要看下PowerManager创建锁这部分：

newWakeLock(int levelAndFlags, String tag)

levelAndFlags： 就是上边表格中的几个flag，可以看到不同的flag对系统的影响并不一样

 

PARTIAL_WAKE_LOCK： 保持cpu运转状态，屏幕键盘灭，按power键该锁不会被系统自动释放，所以系统无法进去待机休眠

SCREEN_DIM_WAKE_LOCK： 保持cpu处于运行状态，屏幕微亮、键盘灭，但是按power键进入待机休眠时会自动释放

SCREEN_BRIGHT_WAKE_LOCK： 保持cpu处于运行状态，屏幕亮、键盘灭，但是按power键进入待机休眠时会自动释放

FULL_WAKE_LOCK： 保持cpu处于运行状态，屏幕、键盘亮，但是按power键进入待机休眠时会自动释放

 

注意：官方的文档介绍尽量不要使用WAKE_LOCK，用FLAG_KEEP_SCREEN_ON标志位代替WAKE_LOCK，用如下方式：

1 getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

当然该方法只是针对当前Activity，如果要整个应用都保持屏幕亮，则可以写了BaseActivity并设置该标志位，其他Activity继承BaseActivity即可。

四、PowerManagerService调试

PMS中最容易出现的问题就是待机待不下去，原因很可能就是获取的WAKE_LOCK没有及时释放，如果待机时有如下的锁的话是没法正真进去待机的，如果出现这种情况，按理说是应该在应用在进去待机时释放锁的

 

五、总结

总的来说PMS的流程并不复杂，不过需要静下心来分析代码仍然不是一件很容易的事情，关于updatePowerStateLocked()方法暂时还没写上去，感觉东西挺多的一下子写上去会显得很长，但是不仔细分析又感觉没必要写，所以就先空着，过两天再补上吧。本人水平有限，有不足之处请指出，后续我会持续更新修改。