WakeLock的acquire 和 电源更新状态

  // Dirty bit: mWakeLocks changed

    private static final int DIRTY_WAKE_LOCKS = 1 << 0;
    // Dirty bit: mWakefulness changed
    private static final int DIRTY_WAKEFULNESS = 1 << 1;
    // Dirty bit: user activity was poked or may have timed out
    private static final int DIRTY_USER_ACTIVITY = 1 << 2;
    // Dirty bit: actual display power state was updated asynchronously
    private static final int DIRTY_ACTUAL_DISPLAY_POWER_STATE_UPDATED = 1 << 3;
    // Dirty bit: mBootCompleted changed
    private static final int DIRTY_BOOT_COMPLETED = 1 << 4;
    // Dirty bit: settings changed
    private static final int DIRTY_SETTINGS = 1 << 5;
    // Dirty bit: mIsPowered changed
    private static final int DIRTY_IS_POWERED = 1 << 6;
    // Dirty bit: mStayOn changed
    private static final int DIRTY_STAY_ON = 1 << 7;
    // Dirty bit: battery state changed
    private static final int DIRTY_BATTERY_STATE = 1 << 8;
    // Dirty bit: proximity state changed
    private static final int DIRTY_PROXIMITY_POSITIVE = 1 << 9;
    // Dirty bit: dock state changed
    private static final int DIRTY_DOCK_STATE = 1 << 10;
    // Dirty bit: brightness boost changed

    private static final int DIRTY_SCREEN_BRIGHTNESS_BOOST = 1 << 11;

WakeLock类中实现acquire()和release()方法实际上是调用了PowerManagerService的acquireWakeLock()和releaseWakeLock()方法。

updatePowerStateLocked为PowerManagerService的核心函数；

在执行完申请锁，释放锁，用户事件，强制唤醒/睡眠等操作都需要调用updatePowerStateLocked()来更新电源状态。

private void updatePowerStateLocked() {

    //… …省略

    // Phase 0: Basic state updates.
    // 基本状态更新
    updateIsPoweredLocked(mDirty);//BatteryManagerInternal–BatteryService 哪种充电方式 （ac交流、usb充电、无线）<integer name=”config_lowBatteryWarningLevel”>15</integer> 低电池的警告
    updateStayOnLocked(mDirty); // 是否有开启”充电保持唤醒”功能

    // Phase 1: Update wakefulness.
    // Loop because the wake lock and user activity computations are influenced
    // by changes in wakefulness.
    final long now = SystemClock.uptimeMillis();
    int dirtyPhase2 = 0;
    for (;;) {

        int dirtyPhase1 = mDirty;
        dirtyPhase2 |= dirtyPhase1;
        mDirty = 0;
        //检查当前系统中所有激活的(没有释放)WakeLock
        updateWakeLockSummaryLocked(dirtyPhase1);
        //更新主动申请的系统状态如bright/dim
        updateUserActivitySummaryLocked(now, dirtyPhase1);
        // 如果经过前面的检查和更新后，没有新的状态变更则退出循环准备休眠
        if (!updateWakefulnessLocked(dirtyPhase1)) {

            break;
        }
    }

    // Phase 2: Update dreams and display power state.
    // 更新dream屏保状态
    updateDreamLocked(dirtyPhase2);
    // 更新显示状态，包含关闭/点亮屏幕
    updateDisplayPowerStateLocked(dirtyPhase2);

    // Phase 3: Send notifications, if needed.
    // 休眠/唤醒是否准备完成
    if (mDisplayReady) {

        sendPendingNotificationsLocked();
    }

    // Phase 4: Update suspend blocker.
    // Because we might release the last suspend blocker here, we need to make sure
    // we finished everything else first!
    // 休眠/唤醒前最后一步，之后会跳转到native层执行申请/释放锁的操作
    updateSuspendBlockerLocked();

}