[移动开发]Android 电池管理(BatteryService) 详解

SystemServer在启动BatteryService时，一次会调用它的构造函数，onStart，onBootPhase方法;解析来我们分析一下这些方法：
1.Constructor方法：
public BatteryService(Context context) {
    super(context);
    mContext = context;
    mHandler = new Handler(true /*async*/);
    //电源呼吸灯
    mLed = new Led(context, getLocalService(LightsManager.class));
    //BatteryStatsService服务，用于统计服务
    mBatteryStats = BatteryStatsService.getService();
    //AMS本地服务
    mActivityManagerInternal = 
            LocalServices.getService(ActivityManagerInternal.class);
    //电量警告值,该值为5
    mCriticalBatteryLevel = mContext.getResources().getInteger(
            com.android.internal.R.integer.config_criticalBatteryWarningLevel);
    //低电量警告值，该值为15
    mLowBatteryWarningLevel = mContext.getResources().getInteger(
            com.android.internal.R.integer.config_lowBatteryWarningLevel);
    //关闭低电量警告的值，为20
    mLowBatteryCloseWarningLevel = mLowBatteryWarningLevel + 
            mContext.getResources().getInteger(
            com.android.internal.R.integer.config_lowBatteryCloseWarningBump);
    //高温关机的温度值，该值为68C
    mShutdownBatteryTemperature = mContext.getResources().getInteger(
            com.android.internal.R.integer.config_shutdownBatteryTemperature);
    //设置UEvents监听，监听kernel层上传的无效charge信息
    // watch for invalid charger messages if the invalid_charger switch exists
    if (new File("/sys/devices/virtual/switch/invalid_charger/state").exists()) {
        UEventObserver invalidChargerObserver = new UEventObserver() {
            @Override
            public void onUEvent(UEvent event) {
                final int invalidCharger = "1".equals(
                    event.get("SWITCH_STATE")) ? 1 : 0;
                synchronized (mLock) {
                    if (mInvalidCharger != invalidCharger) {
                        mInvalidCharger = invalidCharger;
                    }
                }
            }
        };
        invalidChargerObserver.startObserving(
                "DEVPATH=/devices/virtual/switch/invalid_charger");
    }
}
UEvent机制：UEvent机制时kernel通知用户空间的一种机制，很多地方都用到了UEvent机制，入USB插拔/充电等，其本质是内核发送一个字符串(可通过Socket), 应用层接收解释该字符串，获取相应的信息，如果信息有变化，onUEvent方法触发，做出改变；
使用UEvent机制时，需要一个UEventObserver对象，并重写onUEvent(UEvent e)方法，然后调用startObserving方法进行监听，当一个uevent匹配startObserving方法中指定的字符串时触发onUEvent方法；

2.onStart方法：
public void onStart() {
    //获取注册时名为“batteryproperties”的服务
    IBinder b = ServiceManager.getService("batteryproperties");
    final IBatteryPropertiesRegistrar batteryPropertiesRegistrar =
            IBatteryPropertiesRegistrar.Stub.asInterface(b);
    try {
        batteryPropertiesRegistrar.registerListener(new BatteryListener());
    } catch (RemoteException e) {
        // Should never happen.
    }
    mBinderService = new BinderService();
    //发布Binder服务
    publishBinderService("battery", mBinderService);
    //发布本地服务
    publishLocalService(BatteryManagerInternal.class, new LocalService());
}
首先获取一个"batteryproperties"的Binder，也即BatteryPropertiesRegistrar，这个服务由healthd层进行注册，底层间隔1分钟，会通过这个服务将电量状态信息更新给BatteryService；
然后，实例化内部类BinderService，该类继承自Binder，然后将这个Binder通过PublishBinderService方法发布到系统服务中;
publishLocalService方法中将BatterySevice的内部类LocalService注册到本地服务；LocalService中提供了一些获取电池相关的方法，且仅限于SystemServer进程内使用;

onBootPhase方法：
public void onBootPhase(int phase) {
    if (phase == PHASE_ACTIVITY_MANAGER_READY) {
        // check our power situation now that it is safe to display the shutdown dialog.
        synchronized (mLock) {
            //注册一个低电量监听
            ContentObserver obs = new ContentObserver(mHandler) {
                @Override
                public void onChange(boolean selfChange) {
                    synchronized (mLock) {
                        updateBatteryWarningLevelLocked();
                    }
                }
            };
            final ContentResolver resolver = mContext.getContentResolver();
            resolver.registerContentObserver(Settings.Global.getUriFor(
                    Settings.Global.LOW_POWER_MODE_TRIGGER_LEVEL),
                    false, obs, UserHandle.USER_ALL);
            updateBatteryWarningLevelLocked();
        }
    }
}
这个方法中设置了ContentObserver观察者，当Settings.Global中低电量触发值改变时，就会触发onChange方法，根据上面分析；

接下来分析updateBatteryWarningLevelLocked方法：
private void updateBatteryWarningLevelLocked() {
    final ContentResolver resolver = mContext.getContentResolver();
    //获取配置文件中存储的低电量触发默认值,15
    int defWarnLevel = mContext.getResources().getInteger(
            com.android.internal.R.integer.config_lowBatteryWarningLevel);
    //获取Settings.Global中存储的低电量触发值
    mLowBatteryWarningLevel = Settings.Global.getInt(resolver,
            Settings.Global.LOW_POWER_MODE_TRIGGER_LEVEL, defWarnLevel);
    if (mLowBatteryWarningLevel == 0) {
        mLowBatteryWarningLevel = defWarnLevel;
    }
    if (mLowBatteryWarningLevel < mCriticalBatteryLevel) {
        mLowBatteryWarningLevel = mCriticalBatteryLevel;
    }
    mLowBatteryCloseWarningLevel = mLowBatteryWarningLevel + mContext.getResources().getInteger(
            com.android.internal.R.integer.config_lowBatteryCloseWarningBump);
    //更新电池状态信息的核心方法
    processValuesLocked(true);
}

调用更新电池状态信息的核心方法processValuesLocked()：
这个是BatteryService最核心的方法，当healthd从kernel层获取电池信息后，会上报给BatteryService，BatteryService中通过这个方法进行处理从而完成更新;
再BatteryService中，有三个地方调用了processValuesLocked方法
1.启动BatteryService时，在onBootPhase方法中的updateBatteryWainingLock方法中;
2.在healthd层向BatteryService更新电池状态信息的update方法中，这里每分钟调用一次；
3.通过adb shell命令dump时在processValuesFromShellLocked方法中;

由于该方法体量较大，我们将分段分析：
1.获取充电类型：
mBatteryLevelCritical = (mBatteryProps.batteryLevel <= mCriticalBatteryLevel);
//获取充电类型
if (mBatteryProps.chargerAcOnline) {
    //AC充电
    mPlugType = BatteryManager.BATTERY_PLUGGED_AC;
} else if (mBatteryProps.chargerUsbOnline) {
    //USB充电
    mPlugType = BatteryManager.BATTERY_PLUGGED_USB;
} else if (mBatteryProps.chargerWirelessOnline) {
    //无线充电
    mPlugType = BatteryManager.BATTERY_PLUGGED_WIRELESS;
} else {
    //没有充电
    mPlugType = BATTERY_PLUGGED_NONE;
}

2.更新统计电池状态信息：
try {
    //将电池信息交给BatteryStatsService进行统计
    mBatteryStats.setBatteryState(mBatteryProps.batteryStatus,
            mBatteryProps.batteryHealth,
            mPlugType, mBatteryProps.batteryLevel, 
            mBatteryProps.batteryTemperature,
            mBatteryProps.batteryVoltage, mBatteryProps.batteryChargeCounter,
            mBatteryProps.batteryFullCharge);
} catch (RemoteException e) {
    // Should never happen.
}
这里将BatteryProperties中更新的电池信息更新到BatteryStatesService中进行统计;
BatteryProperties是由healthd中传入，实现了Parcelable接口，里面存储了healthd从节点文件中读取的电池信息；

3.进行低电量时和高温时的关机：
//低电量关机
shutdownIfNoPowerLocked();
//高温关机
shutdownIfOverTempLocked();
在电量为0并且没有充电时，会自动关机，当温度高于68时，也会进行自动关机;

4.充电类型改变时获取放电时长和放电量：
if (mPlugType != mLastPlugType) {
    //上次没充电，说明设备由放电进入充电状态
    if (mLastPlugType == BATTERY_PLUGGED_NONE) {
        /**
         * mDischargeStartTime默认为0，在充电进入放电时赋值为当前时间，放电进入
         *充电时又赋值为0
         * mDischargeStartLevel为开始放电时的电量
         * mDischargeStartTime != 0说明有一次充电->放电
         * mDischargeStartLevel！=mBatteryProps.batteryLevel说明电池电量有改变
         */
        if (mDischargeStartTime != 0 && mDischargeStartLevel != 
                       mBatteryProps.batteryLevel) {
            //放电时间段 = 当前时间 - 开始放电时间
            dischargeDuration = SystemClock.elapsedRealtime() - 
                       mDischargeStartTime;
            //重新赋值为0
            mDischargeStartTime = 0;
        }
    } else if (mPlugType == BATTERY_PLUGGED_NONE) {//放电->充电
        // charging -> discharging or we just powered up
        //重新赋值为当前时间
        mDischargeStartTime = SystemClock.elapsedRealtime();
        //重新赋值为当前电量
        mDischargeStartLevel = mBatteryProps.batteryLevel;
    }
}

5.更新低电量临界值：
if (!mBatteryLevelLow) {
    // Should we now switch in to low battery mode?
    //没充电且当前电量小于等于15%
    if (mPlugType == BATTERY_PLUGGED_NONE
            && mBatteryProps.batteryLevel <= mLowBatteryWarningLevel) {
        mBatteryLevelLow = true;
    }
} else {
    //充电时mBatteryLevelLow置为false，退出低电量模式
    if (mPlugType != BATTERY_PLUGGED_NONE) {
        mBatteryLevelLow = false;
        //电量到达20%，退出低电量模式
    } else if (mBatteryProps.batteryLevel >= mLowBatteryCloseWarningLevel)  {
        mBatteryLevelLow = false;
        //force为true时进行强制更新
    } else if (force && mBatteryProps.batteryLevel >= mLowBatteryWarningLevel) {
        mBatteryLevelLow = false;
    }
}
mBatteryLevelLow是一个用于判断当前电量是否小于低电量警告值得boolean值，和低电量模式有关，在PMS中设置低电量模式时，都会通过LocalService获取到这个值；

6.发送充电/放电模式和到达低电量/退出低电量广播：
/**
 *放电->充电,发送Intent.ACTION_POWER_CONNECTED广播,mSequence每次都会+1,
 *用于记录广播次序，和JobScheduler有关
 *
 *充电->放电,发送Intent.ACTION_POWER_DISCONNECTED广播
 */
if (mPlugType != 0 && mLastPlugType == 0) {
    final Intent statusIntent = new Intent(Intent.ACTION_POWER_CONNECTED);
    statusIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_
                     ONLY_BEFORE_BOOT);
    statusIntent.putExtra(BatteryManager.EXTRA_SEQUENCE, mSequence);
    mHandler.post(new Runnable() {
        @Override
        public void run() {
            mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL);
        }
    });
}
else if (mPlugType == 0 && mLastPlugType != 0) {
    final Intent statusIntent = new Intent(Intent.ACTION_POWER_DISCONNECTED);
    statusIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_
           BEFORE_BOOT);
    statusIntent.putExtra(BatteryManager.EXTRA_SEQUENCE, mSequence);
    mHandler.post(new Runnable() {
        @Override
        public void run() {
            mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL);
        }
    });
}
/**
 * 发送电池电量过低广播Intent.ACTION_BATTERY_LOW，该广播在两种情况下发送：
 * 1.设备由充电进入放电(拔掉充电器)后，电量小于15%
 * 2.设备在放电过程中，电量小于15%
 *
 * 当电量达到20%时，发送电池状态正常广播Intent.ACTION_BATTERY_OKAY
 */
if (shouldSendBatteryLowLocked()) {
    mSentLowBatteryBroadcast = true;
    final Intent statusIntent = new Intent(Intent.ACTION_BATTERY_LOW);
    statusIntent.setFlags(Intent.
                   FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
    statusIntent.putExtra(BatteryManager.EXTRA_SEQUENCE, mSequence);
    mHandler.post(new Runnable() {
        @Override
        public void run() {
            mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL);
        }
    });
} else if (mSentLowBatteryBroadcast &&
        mBatteryProps.batteryLevel >= mLowBatteryCloseWarningLevel) {
    mSentLowBatteryBroadcast = false;
    final Intent statusIntent = new Intent(Intent.ACTION_BATTERY_OKAY);
    statusIntent.setFlags(Intent.
                   FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
    statusIntent.putExtra(BatteryManager.EXTRA_SEQUENCE, mSequence);
    mHandler.post(new Runnable() {
        @Override
        public void run() {
            mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL);
        }
    });
}

7.调用sendIntentLocked方法发送粘性广播：该广播持续性的发送电池电量的变化
private void sendIntentLocked() {
    //  Pack up the values and broadcast them to everyone
    final Intent intent = new Intent(Intent.ACTION_BATTERY_CHANGED);
    intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY
            | Intent.FLAG_RECEIVER_REPLACE_PENDING);
    int icon = getIconLocked(mBatteryProps.batteryLevel);
    intent.putExtra(BatteryManager.EXTRA_SEQUENCE, mSequence);
    intent.putExtra(BatteryManager.EXTRA_STATUS, mBatteryProps.batteryStatus);
    intent.putExtra(BatteryManager.EXTRA_HEALTH, mBatteryProps.batteryHealth);
    intent.putExtra(BatteryManager.EXTRA_PRESENT, mBatteryProps.batteryPresent);
    intent.putExtra(BatteryManager.EXTRA_LEVEL, mBatteryProps.batteryLevel);
    intent.putExtra(BatteryManager.EXTRA_SCALE, BATTERY_SCALE);
    intent.putExtra(BatteryManager.EXTRA_ICON_SMALL, icon);
    intent.putExtra(BatteryManager.EXTRA_PLUGGED, mPlugType);
    intent.putExtra(BatteryManager.EXTRA_VOLTAGE, mBatteryProps.batteryVoltage);
    intent.putExtra(BatteryManager.EXTRA_TEMPERATURE, 
                         mBatteryProps.batteryTemperature);
    intent.putExtra(BatteryManager.EXTRA_TECHNOLOGY, 
                         mBatteryProps.batteryTechnology);
    intent.putExtra(BatteryManager.EXTRA_INVALID_CHARGER, mInvalidCharger);
    intent.putExtra(BatteryManager.EXTRA_MAX_CHARGING_CURRENT, 
                         mBatteryProps.maxChargingCurrent);
    intent.putExtra(BatteryManager.EXTRA_MAX_CHARGING_VOLTAGE, 
                         mBatteryProps.maxChargingVoltage);
    intent.putExtra(BatteryManager.EXTRA_CHARGE_COUNTER, 
                         mBatteryProps.batteryChargeCounter);
    mHandler.post(new Runnable() {
        @Override
        public void run() {
            ActivityManager.broadcastStickyIntent(intent, UserHandle.USER_ALL);
        }
    });
}

8.更新LED灯状态：
mLed.updateLightsLocked();
public void updateLightsLocked() {
    final int level = mBatteryProps.batteryLevel;
    final int status = mBatteryProps.batteryStatus;
    //电量<15%
    if (level < mLowBatteryWarningLevel) {
        //电池状态处于充电状态
        if (status == BatteryManager.BATTERY_STATUS_CHARGING) {
            // Solid red when battery is charging
            mBatteryLight.setColor(mBatteryLowARGB);
        } else {
            // Flash red when battery is low and not charging
            mBatteryLight.setFlashing(mBatteryLowARGB, Light.LIGHT_FLASH_TIMED,
                    mBatteryLedOn, mBatteryLedOff);
        }
        //电池状态处于充电状态||满电量状态
    } else if (status == BatteryManager.BATTERY_STATUS_CHARGING
            || status == BatteryManager.BATTERY_STATUS_FULL) {
        //处于满电亮状态，或者电量大于90%
        if (status == BatteryManager.BATTERY_STATUS_FULL || level >= 90) {
            // Solid green when full or charging and nearly full
            mBatteryLight.setColor(mBatteryFullARGB);
        } else {//电量小于90且充电
            // Solid orange when charging and halfway full
            mBatteryLight.setColor(mBatteryMediumARGB);
        }
    } else {//不处于充电状态
        // No lights if not charging and not low
        mBatteryLight.turnOff();
    }
}

9.更新电池信息：
mLastBatteryStatus = mBatteryProps.batteryStatus;
mLastBatteryHealth = mBatteryProps.batteryHealth;
mLastBatteryPresent = mBatteryProps.batteryPresent;
mLastBatteryLevel = mBatteryProps.batteryLevel;
mLastPlugType = mPlugType;
mLastBatteryVoltage = mBatteryProps.batteryVoltage;
mLastBatteryTemperature = mBatteryProps.batteryTemperature;
mLastMaxChargingCurrent = mBatteryProps.maxChargingCurrent;
mLastMaxChargingVoltage = mBatteryProps.maxChargingVoltage;
mLastChargeCounter = mBatteryProps.batteryChargeCounter;
mLastBatteryLevelCritical = mBatteryLevelCritical;
mLastInvalidCharger = mInvalidCharger;
至此，BatteryService得启动流程和和核心方法就分析完比了，现在剩余内部类BatteryListener了；

BatteryService.BatteryListener：
在分析batteryService得启动过程时，对onStart方法中得IBatteryPropertiesRegistrar和BatteryListener没有深入得分析说明，现在主要研究它们之间的关系和作用；

回到onStart方法中：
public void onStart() {
    //获取名为“batteryproperties”的服务
    IBinder b = ServiceManager.getService("batteryproperties");
    final IBatteryPropertiesRegistrar batteryPropertiesRegistrar =
            IBatteryPropertiesRegistrar.Stub.asInterface(b);
    try {
        batteryPropertiesRegistrar.registerListener(new BatteryListener());
    } catch (RemoteException e) {
        // Should never happen.
    }
    ......
}

首先，在系统服务中获取batteryproperties注册的服务，获取到的对象为Binder，那么这个名为batteryProperties的系统服务，它是在何处注册的呢?
在C++的代码中，找到了batteryProperties注册位置：
\system\core\healthd\BatteryPropertiesRegistrar.cpp
void BatteryPropertiesRegistrar::publish(
    const sp<BatteryPropertiesRegistrar>& service) {
    defaultServiceManager()->addService(String16("batteryproperties"), service);
}

之后对IBatteryPropertiesRegistrar注册一个监听事件，当监听内容改变时回调对应的方法，监听器如下：
private final class BatteryListener extends IBatteryPropertiesListener.Stub {
    @Override public void batteryPropertiesChanged(BatteryProperties props) {
        final long identity = Binder.clearCallingIdentity();
        try {
            BatteryService.this.update(props);
        } finally {
            Binder.restoreCallingIdentity(identity);
        }
   }
}

可以看到，BatteryListener继承于IBatteryPropertiesListener.Stub，因此也是一个Binder对象，当监听内容发生变化时，回调方法batteryPropertiesChanged方法中调用update方法：
private void update(BatteryProperties props) {
    synchronized (mLock) {
        if (!mUpdatesStopped) {
            mBatteryProps = props;
            // Process the new values.
            processValuesLocked(false);
        } else {
            mLastBatteryProps.set(props);
        }
    }
}
在这个方法中，通过监听器传入到BatteryProperties初始化成员变量mBatteryProps；BatteryProperties中带有电池状态信息，通过该方法最终调用processValuesLocked方法，从而完成电池状态信息的更新;

参考文档：
电池服务管理-详解

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