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。
时间： 2024-10-20 01:28:01