【Android 10 源码】healthd 模块 BatteryService 初始化

BatteryService 是在 SystemServer 中启动的，BatteryService 监控设备电池的充电状态和充电水平。当这些值改变时，这个服务会将这些新值广播给所有正在监听 ACTION_BATTERY_CHANGED 的广播接收者。

BatteryService 被划分到核心服务类别。

frameworks/base/services/java/com/android/server/SystemServer.java

public final class SystemServer {......private void startCoreServices() {traceBeginAndSlog("StartBatteryService");// Tracks the battery level.  Requires LightService.mSystemServiceManager.startService(BatteryService.class);traceEnd();......}......
}

SystemServiceManager startService(Class serviceClass) 通过反射的方式构造了 BatteryService。构造完后就会调用其重载版本的函数 startService(@NonNull final SystemService service) 正在启动它。

frameworks/base/services/core/java/com/android/server/SystemServiceManager.java

public class SystemServiceManager {......@SuppressWarnings("unchecked")public <T extends SystemService> T startService(Class<T> serviceClass) {try {final String name = serviceClass.getName();Slog.i(TAG, "Starting " + name);Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartService " + name);// Create the service.if (!SystemService.class.isAssignableFrom(serviceClass)) {throw new RuntimeException("Failed to create " + name+ ": service must extend " + SystemService.class.getName());}final T service;try {Constructor<T> constructor = serviceClass.getConstructor(Context.class);service = constructor.newInstance(mContext);} catch (InstantiationException ex) {throw new RuntimeException("Failed to create service " + name+ ": service could not be instantiated", ex);} catch (IllegalAccessException ex) {throw new RuntimeException("Failed to create service " + name+ ": service must have a public constructor with a Context argument", ex);} catch (NoSuchMethodException ex) {throw new RuntimeException("Failed to create service " + name+ ": service must have a public constructor with a Context argument", ex);} catch (InvocationTargetException ex) {throw new RuntimeException("Failed to create service " + name+ ": service constructor threw an exception", ex);}startService(service);return service;} finally {Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);}}public void startService(@NonNull final SystemService service) {// Register it.mServices.add(service);// Start it.long time = SystemClock.elapsedRealtime();try {service.onStart();} catch (RuntimeException ex) {throw new RuntimeException("Failed to start service " + service.getClass().getName()+ ": onStart threw an exception", ex);}warnIfTooLong(SystemClock.elapsedRealtime() - time, service, "onStart");}......
}

从上图中的 BatteryService 作用不难看出其承上启下，向上给 BatteryManager 提供支撑，向下则通过静态内部类 HealthServiceWrapper 连接 HAL。

BatteryService 构造函数中获取到了 BatteryStatsService 代理，电池 Led 控制类，AMS 内部接口类 ActivityManagerInternal。以及一些关键电量配置参数：

mCriticalBatteryLevel —— 电池危急电量（当电池电量下降到这个值时，显示低电量警告，在设备关闭之前，用于确定何时做最后的努力来记录放电状态）

mLowBatteryWarningLevel —— 电池低电量警告电量

mLowBatteryCloseWarningLevel —— 关闭低电量警告电量

mShutdownBatteryTemperature —— 电池过热触发关机温度

另外，还注册了一个监听无效充电器的消息订阅者。前提是 /sys/devices/virtual/switch/invalid_charger/state 路径存在。