Android电源管理系列之PowerManagerService(二)
WakeLock机制
PowerManager.WakeLock
为了延长电池的使用寿命,Android设备会在一段时间后使屏幕变暗,然后关闭屏幕显示,直至停止CPU进入休眠。WakeLock是Android提供的唤醒锁机制,用来保持CPU运行或避免屏幕变暗/关闭以及避免键盘背光灯熄灭
唤醒锁的类型:
Flag | CPU | Screen | Keyboard |
---|---|---|---|
PARTIAL_WAKE_LOCK | on | off | off |
SCREEN_DIM_WAKE_LOCK | on | Dim | off |
SCREEN_BRIGHT_WAKE_LOCK | on | Bright | off |
FULL_WAKE_LOCK | on | Bright | on |
如果是PARTIAL_WAKE_LOCK,无论屏幕的状态或是按下电源键, CPU都将正常工作。如果是其它的唤醒锁,设备会在用户按下电源钮后停止工作进入休眠状态。以上四种锁,除了PARTIAL_WAKE_LOCK,其余的锁在API level 17已经被deprecated了。
唤醒锁的使用方法
代码使用:
PowerManager powerManager = (PowerManager) getSystemService(Context.POWER_SERVICE);
PowerManager.WakeLock wl = powerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "My Tag");
wl.acquire(); //acquire时尽量申明timeout时间// ... do work...wl.release();
权限申明:
<uses-permission android:name="android.permission.WAKE_LOCK" /><uses-permission android:name="android.permission.DEVICE_POWER"/>
在应用程序中使用WakeLock时必须申明权限,acquire请求唤醒锁时尽量设置timeout时间释放WakeLock,以避免长时间持有WakeLock导致系统无法休眠。
唤醒锁的实现:frameworks/base/core/java/android/os/PowerManager.java
public final class WakeLock { private int mFlags; private String mTag; private final String mPackageName; private final IBinder mToken; private int mCount; private boolean mRefCounted = true; private boolean mHeld; private WorkSource mWorkSource; private String mHistoryTag; private final String mTraceName;
......
WakeLock(int flags, String tag, String packageName) {
mFlags = flags;
mTag = tag;
mPackageName = packageName;
mToken = new Binder();
mTraceName = "WakeLock (" + mTag + ")";
}
......
}
updatePowerStateLocked
frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java
protected void updatePowerStateLocked() { // 服务没有ready,mDirty值没有设置情况下不做更新操作
if (!mSystemReady || mDirty == 0) { return;
} if (!Thread.holdsLock(mLock)) {
Slog.wtf(TAG, "Power manager lock was not held when calling updatePowerStateLocked");
} try { // Phase 0: 更新基本状态
updateIsPoweredLocked(mDirty);
updateStayOnLocked(mDirty);
updateScreenBrightnessBoostLocked(mDirty); // 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;
updateWakeLockSummaryLocked(dirtyPhase1);
updateUserActivitySummaryLocked(now, dirtyPhase1); if (!updateWakefulnessLocked(dirtyPhase1)) { break;
}
} // Phase 2: Update display power state.
boolean displayBecameReady = updateDisplayPowerStateLocked(dirtyPhase2); // Phase 3: Update dream state (depends on display ready signal).
updateDreamLocked(dirtyPhase2, displayBecameReady); // Phase 4: Send notifications, if needed.
finishWakefulnessChangeIfNeededLocked(); // Phase 5: Update suspend blocker.
// Because we might release the last suspend blocker here, we need to make sure
// we finished everything else first!
updateSuspendBlockerLocked();
} finally {
Trace.traceEnd(Trace.TRACE_TAG_POWER);
}
}
首先来看updateIsPoweredLocked(mDirty);
private void updateIsPoweredLocked(int dirty) { if ((dirty & DIRTY_BATTERY_STATE) != 0) { final boolean wasPowered = mIsPowered; final int oldPlugType = mPlugType; final boolean oldLevelLow = mBatteryLevelLow;
mIsPowered = mBatteryManagerInternal.isPowered(BatteryManager.BATTERY_PLUGGED_ANY);
mPlugType = mBatteryManagerInternal.getPlugType();
mBatteryLevel = mBatteryManagerInternal.getBatteryLevel();
mBatteryLevelLow = mBatteryManagerInternal.getBatteryLevelLow(); if (wasPowered != mIsPowered || oldPlugType != mPlugType) {
mDirty |= DIRTY_IS_POWERED; // Update wireless dock detection state.
final boolean dockedOnWirelessCharger = mWirelessChargerDetector.update(
mIsPowered, mPlugType, mBatteryLevel); // Treat plugging and unplugging the devices as a user activity.
// Users find it disconcerting when they plug or unplug the device
// and it shuts off right away.
// Some devices also wake the device when plugged or unplugged because
// they don't have a charging LED.
final long now = SystemClock.uptimeMillis(); if (shouldWakeUpWhenPluggedOrUnpluggedLocked(wasPowered, oldPlugType,
dockedOnWirelessCharger)) {
wakeUpNoUpdateLocked(now, "android.server.power:POWER", Process.SYSTEM_UID,
mContext.getOpPackageName(), Process.SYSTEM_UID);
}
userActivityNoUpdateLocked(
now, PowerManager.USER_ACTIVITY_EVENT_OTHER, 0, Process.SYSTEM_UID); // Tell the notifier whether wireless charging has started so that
// it can provide feedback to the user.
//Bug293654, zhanghong.wt, modify, 20170914, modify no notificatin ring while plugging USB
if (dockedOnWirelessCharger || (mIsPowered && oldPlugType != mPlugType&&("1".equals(SystemProperties.get("sys.boot_completed"))))) {
mNotifier.onWirelessChargingStarted();
}
} if (wasPowered != mIsPowered || oldLevelLow != mBatteryLevelLow) { if (oldLevelLow != mBatteryLevelLow && !mBatteryLevelLow) { if (DEBUG_SPEW) {
Slog.d(TAG, "updateIsPoweredLocked: resetting low power snooze");
}
mAutoLowPowerModeSnoozing = false;
}
updateLowPowerModeLocked();
}
}
}
最后附上PowerManagerService 总结图

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Android电源管理系列之PowerManagerService(一)
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/...
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