Android电源管理系列之PowerManagerService启动

PowerManagerService 提供Android系统的电源管理服务，主要功能是控制系统待机状态，屏幕显示，亮度调节，光线/距离传感器的控制等。
相关代码在以下文件中：

frameworks/base/services/java/com/android/server/SystemServer.java
frameworks/base/core/java/android/os/PowerManager.java
frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java
frameworks/base/services/core/jni/com_android_server_power_PowerManagerService.cpp
frameworks/base/core/java/android/os/PowerManagerInternal.java
frameworks/base/services/core/java/com/android/server/power/Notifier.java
device/qcom/common/power/power.c
system/core/libsuspend/autosuspend.c
hardware/libhardware_legacy/power/power.c

初始化流程

跟其他系统服务一样，PowerManagerService也是继承于SystemService并通过SystemServer启动。

SystemServer

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

private void startBootstrapServices() {
  ......
  mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
  ......
}

PowerManagerService

frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java

public final class PowerManagerService extends SystemService
        implements Watchdog.Monitor {
    ......
}

在SystemServer的startBootstrapServices中，通过SystemServiceManager.startService启动了PowerManagerService，下面首先来看PowerManagerService构造方法。
frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java

public PowerManagerService(Context context) {
    super(context);
    // mContext赋值为SystemContext
    mContext = context;
    // 创建消息处理线程并启动，创建关联消息处理线程的handler对象
    mHandlerThread = new ServiceThread(TAG,
            Process.THREAD_PRIORITY_DISPLAY, false /*allowIo*/);
    mHandlerThread.start();
    mHandler = new PowerManagerHandler(mHandlerThread.getLooper());
    qcNsrmPowExt = new QCNsrmPowerExtension(this);
    synchronized (mLock) {
        // 创建"PowerManagerService.WakeLocks"的SuspendBlocker
        mWakeLockSuspendBlocker = createSuspendBlockerLocked("PowerManagerService.WakeLocks");
        // 创建"PowerManagerService.Display"的SuspendBlocker
        mDisplaySuspendBlocker = createSuspendBlockerLocked("PowerManagerService.Display");
        // 请求DisplaySuspendBlocker，禁止系统进入休眠
        mDisplaySuspendBlocker.acquire();
        mHoldingDisplaySuspendBlocker = true;
        mHalAutoSuspendModeEnabled = false;
        mHalInteractiveModeEnabled = true;
        // 设置mWakefulness为唤醒状态
        mWakefulness = WAKEFULNESS_AWAKE;
        // 进入到native层初始化
        nativeInit();
        nativeSetAutoSuspend(false);
        nativeSetInteractive(true);
        nativeSetFeature(POWER_FEATURE_DOUBLE_TAP_TO_WAKE, 0);
    }
}

PowerManagerService构造函数中首先创建了处理消息的进程及对应的handler对象以进行消息处理，然后创建SuspendBlocker对象，用于WakeLocks与Display，
a、PowerManagerService.WakeLocks，主要用于控制CPU的唤醒；
b、PowerManagerService.Display 主要用于控制屏幕的点亮和熄灭；
并设置mWakefulness的初始状态为WAKEFULNESS_AWAKE，
最后进入到native层初始化。下面先看一下关于mWakefulness的定义。

继续回到PowerManagerService构造函数的native初始化中，首先来看nativeInit的实现。
frameworks/base/services/core/jni/com_android_server_power_PowerManagerService.cpp

static const JNINativeMethod gPowerManagerServiceMethods[] = {
    /* name, signature, funcPtr */
    { "nativeInit", "()V",
            (void*) nativeInit },
    { "nativeAcquireSuspendBlocker", "(Ljava/lang/String;)V",
            (void*) nativeAcquireSuspendBlocker },
    { "nativeReleaseSuspendBlocker", "(Ljava/lang/String;)V",
            (void*) nativeReleaseSuspendBlocker },
    { "nativeSetInteractive", "(Z)V",
            (void*) nativeSetInteractive },
    { "nativeSetAutoSuspend", "(Z)V",
            (void*) nativeSetAutoSuspend },
    { "nativeSendPowerHint", "(II)V",
            (void*) nativeSendPowerHint },
    { "nativeSetFeature", "(II)V",
            (void*) nativeSetFeature },
};

PowerManagerService中的native方法定义如上，nativeInit即调用nativeInit()。
frameworks/base/services/core/jni/com_android_server_power_PowerManagerService.cpp

static void nativeInit(JNIEnv* env, jobject obj) {
    // 创建一个全局对象，引用PMS
    gPowerManagerServiceObj = env->NewGlobalRef(obj);
    // 利用hw_get_module加载power模块
    status_t err = hw_get_module(POWER_HARDWARE_MODULE_ID,
            (hw_module_t const**)&gPowerModule);
    if (!err) {
        gPowerModule->init(gPowerModule);
    } else {
        ALOGE("Couldn't load %s module (%s)", POWER_HARDWARE_MODULE_ID, strerror(-err));
    }
}

nativeInit的主要任务时装载power模块，该模块由厂商实现，以高通为例，如下。
device/qcom/common/power/power.c

tatic struct hw_module_methods_t power_module_methods = {
    .open = NULL,
};
 
struct power_module HAL_MODULE_INFO_SYM = {
    .common = {
        .tag = HARDWARE_MODULE_TAG,
        .module_api_version = POWER_MODULE_API_VERSION_0_2,
        .hal_api_version = HARDWARE_HAL_API_VERSION,
        .id = POWER_HARDWARE_MODULE_ID,
        .name = "QCOM Power HAL",
        .author = "Qualcomm",
        .methods = &power_module_methods,
    },
 
    .init = power_init,
    .powerHint = power_hint,
    .setInteractive = set_interactive,
};

power_module中实现了init，powerHint，setInteractive，nativeInit最终调用到HAL power模块的power_init具体实现中。接着看native初始化nativeSetAutoSuspend的实现。
frameworks/base/services/core/jni/com_android_server_power_PowerManagerService.cpp

static void nativeSetAutoSuspend(JNIEnv* /* env */, jclass /* clazz */, jboolean enable) {
    if (enable) {
        ALOGD_IF_SLOW(100, "Excessive delay in autosuspend_enable() while turning screen off");
        autosuspend_enable();
    } else {
        ALOGD_IF_SLOW(100, "Excessive delay in autosuspend_disable() while turning screen on");
        autosuspend_disable();
    }
}

system/core/libsuspend/autosuspend.c

int autosuspend_disable(void)
{
    int ret;
 
    ret = autosuspend_init();
    if (ret) {
        return ret;
    }
 
    ALOGV("autosuspend_disable\n");
 
    if (!autosuspend_enabled) {
        return 0;
    }
 
    ret = autosuspend_ops->disable();
    if (ret) {
        return ret;
    }
 
    autosuspend_enabled = false;
    return 0;
}

nativeSetAutoSuspend最终调用到libsuspend(参考Android电源管理系列之libsuspend)的autosuspend_disable禁止系统休眠。继续看native初始化nativeSetInteractive，nativeSetFeature的实现。
frameworks/base/services/core/jni/com_android_server_power_PowerManagerService.cpp

static void nativeSetInteractive(JNIEnv* /* env */, jclass /* clazz */, jboolean enable) {
    if (gPowerModule) {
        if (enable) {
            ALOGD_IF_SLOW(20, "Excessive delay in setInteractive(true) while turning screen on");
            gPowerModule->setInteractive(gPowerModule, true);
        } else {
            ALOGD_IF_SLOW(20, "Excessive delay in setInteractive(false) while turning screen off");
            gPowerModule->setInteractive(gPowerModule, false);
        }
    }
}
 
static void nativeSetFeature(JNIEnv *env, jclass clazz, jint featureId, jint data) {
    int data_param = data;
 
    if (gPowerModule && gPowerModule->setFeature) {
        gPowerModule->setFeature(gPowerModule, (feature_t)featureId, data_param);
    }
}

同nativeInit一样，最终都是调用到HAL power模块的具体实现中。以上是构造函数的分析流程，下面继续看PowerManagerService在系统启动过程中回调onStart()，onBootPhase()，systemReady()的实现。
frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java

public void onStart() {
    publishBinderService(Context.POWER_SERVICE, new BinderService());
    publishLocalService(PowerManagerInternal.class, new LocalService());
 
    Watchdog.getInstance().addMonitor(this);
    Watchdog.getInstance().addThread(mHandler);
}
 
private final class BinderService extends IPowerManager.Stub ｛
    ......
｝
 
private final class LocalService extends PowerManagerInternal {
    ......
}

onStart()中发布了BinderService，LocalService分别供其他进程，进程内其他服务调用，并将PowerManagerService加入到Watchdog监控中。

在system启动的一些阶段，系统会调用如下代码，主动回调SystemService的onBootPhase方法。

mSystemServiceManager.startBootPhase(SystemService.PHASE_XXXXXX);

public class SystemServiceManager {
    public void startBootPhase(final int phase) {
        // 阶段值会随着系统启动的进行越来越大，因此下一个阶段值肯定要大于当前阶段
        if (phase <= mCurrentPhase) {
            throw new IllegalArgumentException("Next phase must be larger than previous");
        } 
        mCurrentPhase = phase; //保存当前阶段

        // 遍历所有的SystemService，并回调它的onBootPhase方法。
        final int serviceLen = mServices.size();
        for (int i = 0; i < serviceLen; i++) {
            final SystemService service = mServices.get(i);
            try {
                service.onBootPhase(mCurrentPhase); // 将阶段值也传进去
            } catch (Exception ex) {
                ...
            }
        }
    }   
}   

PHASE_XXXXXX指示了各个不同的启动阶段，定义如下：

public abstract class SystemService {   
    public static final int PHASE_WAIT_FOR_DEFAULT_DISPLAY = 100;     
    public static final int PHASE_LOCK_SETTINGS_READY = 480;  
    public static final int PHASE_SYSTEM_SERVICES_READY = 500;
    public static final int PHASE_ACTIVITY_MANAGER_READY = 550;
    public static final int PHASE_THIRD_PARTY_APPS_CAN_START = 600;
    public static final int PHASE_BOOT_COMPLETED = 1000;
}

所以，在onBootPhase(int phase)中，我们可以根据phase中指示的启动阶段，做不同的操作！在自己设计新的系统服务时，这个很重要。因为一些操作需要系统环境的支持，有了这个回调函数及phase参数，我们就可以在合适的阶段做合适的操作了。

frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java

public void onBootPhase(int phase) {
    synchronized (mLock) {
        if (phase == PHASE_THIRD_PARTY_APPS_CAN_START) {
            ......
        } else if (phase == PHASE_BOOT_COMPLETED) {
            final long now = SystemClock.uptimeMillis();
            // 设置mBootCompleted状态
            mBootCompleted = true;
            mDirty |= DIRTY_BOOT_COMPLETED;
            // 更新userActivity及PowerState，后面分析
            userActivityNoUpdateLocked(
                    now, PowerManager.USER_ACTIVITY_EVENT_OTHER, 0, Process.SYSTEM_UID);
            updatePowerStateLocked();
            // 执行mBootCompletedRunnables中的runnable方法
            if (!ArrayUtils.isEmpty(mBootCompletedRunnables)) {
                Slog.d(TAG, "Posting " + mBootCompletedRunnables.length + " delayed runnables");
                for (Runnable r : mBootCompletedRunnables) {
                    BackgroundThread.getHandler().post(r);
                }
            }
            mBootCompletedRunnables = null;
        }
    }
}

onBootPhase中主要设置mBootCompleted状态，更新PowerState状态，并执行mBootCompletedRunnables中的runnables方法(低电量模式会设置)。

另外，Java系统服务中一般还会实现一个方法：systemReady()。该方法在SystemServer.java–>startOtherServices()调用：

try {
            // TODO: use boot phase
            mPowerManagerService.systemReady(mActivityManagerService.getAppOpsService());
        } catch (Throwable e) {
            reportWtf("making Power Manager Service ready", e);
        }

frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java

public void systemReady(IAppOpsService appOps) {
    synchronized (mLock) {
        mSystemReady = true;
        // 获取AppOpsService
        mAppOps = appOps;
        // 获取DreamManager
        mDreamManager = getLocalService(DreamManagerInternal.class);
        // 获取DisplayManagerService
        mDisplayManagerInternal = getLocalService(DisplayManagerInternal.class);
        mPolicy = getLocalService(WindowManagerPolicy.class);
        // 获取mBatteryService
        mBatteryManagerInternal = getLocalService(BatteryManagerInternal.class);
 
        PowerManager pm = (PowerManager) mContext.getSystemService(Context.POWER_SERVICE);
        // 获取屏幕默认，最大，最小亮度
        mScreenBrightnessSettingMinimum = pm.getMinimumScreenBrightnessSetting();
        mScreenBrightnessSettingMaximum = pm.getMaximumScreenBrightnessSetting();
        mScreenBrightnessSettingDefault = pm.getDefaultScreenBrightnessSetting();
        // 获取SensorManager
        SensorManager sensorManager = new SystemSensorManager(mContext, mHandler.getLooper());
 
        mBatteryStats = BatteryStatsService.getService();
        // 创建Notifier对象，用于广播power state的变化
        mNotifier = new Notifier(Looper.getMainLooper(), mContext, mBatteryStats,
                mAppOps, createSuspendBlockerLocked("PowerManagerService.Broadcasts"),
                mPolicy);
        // 无线充电检测
        mWirelessChargerDetector = new WirelessChargerDetector(sensorManager,
                createSuspendBlockerLocked("PowerManagerService.WirelessChargerDetector"),
                mHandler);
        // 监听设置的变化
        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 settings changes.
        final ContentResolver resolver = mContext.getContentResolver();
        resolver.registerContentObserver(Settings.Secure.getUriFor(
                Settings.Secure.SCREENSAVER_ENABLED),
        ......
        IVrManager vrManager =
                (IVrManager) getBinderService(VrManagerService.VR_MANAGER_BINDER_SERVICE);
        try {
            vrManager.registerListener(mVrStateCallbacks);
        } catch (RemoteException e) {
            Slog.e(TAG, "Failed to register VR mode state listener: " + e);
        }
        // 读取配置
        readConfigurationLocked();
        updateSettingsLocked();
        mDirty |= DIRTY_BATTERY_STATE;
        updatePowerStateLocked();
    }
 
    // Register for broadcasts from other components of the system.
    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);
}

userActivity

userActivity()接口用于用户进程向PowerManagerService报告用户影响系统休眠的活动。例如， 用户点击屏幕时，系统会调用该方法来告诉PowerManagerService用户点击的时间，这样PowerManagerService将更新内部保存的时间值，从而推迟系统休眠的时间。userActivity()方法主要通过调用内部的userActivityInternal()方法来完成工作。
下面首先来看userActivity的定义。
frameworks/base/core/java/android/os/PowerManager.java

/**
 * User activity event type: Unspecified event type.
 */
public static final int USER_ACTIVITY_EVENT_OTHER = 0;
 
/**
 * User activity event type: Button or key pressed or released.
 */
public static final int USER_ACTIVITY_EVENT_BUTTON = 1;
 
/**
 * User activity event type: Touch down, move or up.
 */
public static final int USER_ACTIVITY_EVENT_TOUCH = 2;
 
/**
 * User activity event type: Accessibility taking action on behalf of user.
 */
public static final int USER_ACTIVITY_EVENT_ACCESSIBILITY = 3;
 
@SystemApi
public void userActivity(long when, int event, int flags) {
    try {
        mService.userActivity(when, event, flags);
    } catch (RemoteException e) {
        throw e.rethrowFromSystemServer();
    }
}

frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java

private final class BinderService extends IPowerManager.Stub {
  ......
  public void userActivity(long eventTime, int event, int flags) {
      final long now = SystemClock.uptimeMillis();
      ......
 
      if (eventTime > now) {
          throw new IllegalArgumentException("event time must not be in the future");
      }
 
      final int uid = Binder.getCallingUid();
      final long ident = Binder.clearCallingIdentity();
      try {
          userActivityInternal(eventTime, event, flags, uid);
      } finally {
          Binder.restoreCallingIdentity(ident);
      }
  }
  ......
}

PowerManager中userActivity请求调用服务端PowerManagerService BinderService的userActivity，即调用内部方法userActivityInternal。
frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java

private void userActivityInternal(long eventTime, int event, int flags, int uid) {
    synchronized (mLock) {
        if (userActivityNoUpdateLocked(eventTime, event, flags, uid)) {
            updatePowerStateLocked();
        }
    }
}

userActivityInternal中首先调用userActivityNoUpdateLocked更新相关数据及状态(userActivityNoUpdateLocked仅仅更新内部状态并不采取任何操作)，然后调用updatePowerStateLocked更新所有PowerState，下面分析userActivityNoUpdateLocked的实现，updatePowerStateLocked是PowerManagerService的核心方法，在最后进行分析。
frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java

private boolean userActivityNoUpdateLocked(long eventTime, int event, int flags, int uid) {
    // 如果发生时间是上一次休眠或唤醒前，或当前没有开机完成到systemReady，不采取操作直接返回
    if (eventTime < mLastSleepTime || eventTime < mLastWakeTime
            || !mBootCompleted || !mSystemReady) {
        return false;
    }
 
    try {
        // 更新mLastInteractivePowerHintTime时间
        if (eventTime > mLastInteractivePowerHintTime) {
            powerHintInternal(POWER_HINT_INTERACTION, 0);
            mLastInteractivePowerHintTime = eventTime;
        }
 
        // 通过mNotifier通知BatteryStats UserActivity事件
        mNotifier.onUserActivity(event, uid);
 
        if (mUserInactiveOverrideFromWindowManager) {
            mUserInactiveOverrideFromWindowManager = false;
            mOverriddenTimeout = -1;
        }
 
        // 已灭屏，或调用该方法带有USER_ACTIVITY_FLAG_INDIRECT，不会更新用户活动时间，不进行处理
        if (mWakefulness == WAKEFULNESS_ASLEEP
                || mWakefulness == WAKEFULNESS_DOZING
                || (flags & PowerManager.USER_ACTIVITY_FLAG_INDIRECT) != 0) {
            return false;
        }
 
        // 根据flag是否在已变暗的情况下是否重启活动超时更新mLastUserActivityTimeNoChangeLights或mLastUserActivityTime，带有USER_ACTIVITY_FLAG_NO_CHANGE_LIGHTS标记时，会延长亮屏一会儿
        // 并且设置mDirty DIRTY_USER_ACTIVITY
        if ((flags & PowerManager.USER_ACTIVITY_FLAG_NO_CHANGE_LIGHTS) != 0) {
            if (eventTime > mLastUserActivityTimeNoChangeLights
                    && eventTime > mLastUserActivityTime) {
                mLastUserActivityTimeNoChangeLights = eventTime;
                mDirty |= DIRTY_USER_ACTIVITY;
                return true;
            }
        } else {
            if (eventTime > mLastUserActivityTime) {
                mLastUserActivityTime = eventTime;
                mDirty |= DIRTY_USER_ACTIVITY;
                return true;
            }
        }
    } finally {
        Trace.traceEnd(Trace.TRACE_TAG_POWER);
    }
    return false;
}

1.何时发生UserActivity

如果我们在Settings中设置sleep时间为15s，那么15秒内如果没有任何操作，屏幕就会熄灭（当然，WakeLock被释放是前提）。如果在这个时间内用户有操作：touch屏幕或者按下菜单键、返回键等，那么这时就会调用PowerManagerService的UserActivity方法，这样会重置那个timeout的时间。

这里有三个重要的时间，参考下图：

首先是screenOffTimeout，一般地，就是设置中的sleep时间，用户可选，有15s、30s、1min、2mins等。device admin和window manager可以override这个时间（PowerManager提供了相应的接口），但是override有要求：必须大于10s，并小于设置中的15s，否则是无意义的，如果这里override了，那么这个就是最终的结果，如果没有override，那么以setting中的为准。在我们后来的讨论中都假设用户选择了15s，而且没有override，所以screenOffTimeout=15s。

其次是screenDimDuration，它代表屏幕亮度处于dim的持续时间（屏幕的变化：bright–dim–off），它是0.2 * 15s=3s。如果用户在settings中设置的不是15s，而是1min，那么1min * 0.2=12s，当大于7s时，取7s。

最后是screenButtonLightDuration，它代表button持续点亮的时间，是0.3 * 15s=4.5s，它也有最大值：8s。

好了，假设在屏幕点亮状态下，我按下了menu键会怎么样呢？会触发UserActivity，同时User activity event type是USER_ACTIVITY_EVENT_BUTTON，那么从按下menu键开始后，button处于点亮状态，screen处于bright首先button的背光持续4.5s点亮，之后熄灭，经过7.5s后screen由bright变为dim，持续3s后，screen off。