【Android休眠】之休眠锁的获取和释放

Linux 3.10
Android 4.4

http://blog.csdn.net/u013686019/article/details/53691895

一、PowerManagerService

引起休眠动作(进入休眠前执行一些必要的操作)的事件有两个：

• PowerKey事件，通过JNI调用PowerManagerService中的goToSleepFromNative()方法

• Timeout，指【设置->显示->休眠】中设置的Timeout数值
  

Android休眠在PowerManagerService中的流程如下图：

图示：最终都会调用到updatePowerStateLocked()方法，在更新一些标志的状态、发送休眠通知后，调用updateSuspendBlockerLocked()执行休眠锁的释放动作。

二、PowerManagerService中Timeout处理流程

/**
 * PowerManagerService设置了很多的标志位，用来标识某个事件的状态是否发生改变，比如：
 * DIRTY_SETTINGS，一旦系统设置发生变化，DIRTY_SETTINGS位就会被设置，
 * 处理函数检测到DIRTY_SETTINGS被置位，就进行相应的动作
 * dirty：包含了所有发生变化的标志
 */
private void updateUserActivitySummaryLocked(long now, int dirty) {
	// Update the status of the user activity timeout timer.
	if ((dirty & (DIRTY_USER_ACTIVITY | DIRTY_WAKEFULNESS | DIRTY_SETTINGS)) != 0) {
		// 1、消息队列中含有尚未处理的MSG_USER_ACTIVITY_TIMEOUT，就移除，避免重复进入休眠操作
		mHandler.removeMessages(MSG_USER_ACTIVITY_TIMEOUT);

		long nextTimeout = 0;
		// 2、mWakefulness != WAKEFULNESS_ASLEEP：当前醒着
		if (mWakefulness != WAKEFULNESS_ASLEEP) {
			// 3、获取Timeout的值，比如30s
			final int screenOffTimeout = getScreenOffTimeoutLocked();
			// 屏幕在熄灭前，会先变暗一段时间，这段时间叫DimDuration，计算方式：
			// SCREEN_DIM_DURATION = 7s，MAXIMUM_SCREEN_DIM_RATIO = 0.2
			// Math.min(SCREEN_DIM_DURATION, (int)(screenOffTimeout * MAXIMUM_SCREEN_DIM_RATIO))
			// 4、获取DimDuration的值，30s x 0.2 = 6s
			final int screenDimDuration = getScreenDimDurationLocked(screenOffTimeout);

			mUserActivitySummary = 0;
			// 5、mLastUserActivityTime >= mLastWakeTime： 用户最后使用机器的时间在上次唤醒时间之后
			if (mLastUserActivityTime >= mLastWakeTime) {
				// nextTimeout：此处指到屏幕Dim的时间间隔
				// 6、nextTimeout的时间：BASE + 30 - 6 = BASE + 24
				nextTimeout = mLastUserActivityTime
						+ screenOffTimeout - screenDimDuration;
				if (now < nextTimeout) {
					// now在屏幕Dim之前，说明屏幕亮着，设置flag
					mUserActivitySummary |= USER_ACTIVITY_SCREEN_BRIGHT;
				} else {
					// extTimeout：此处指到屏幕熄灭的时间间隔
					//7、nextTimeout的时间：BASE + 30 = BASE + 30
					nextTimeout = mLastUserActivityTime + screenOffTimeout;
					// 8、now处于屏幕Dim之后、屏幕熄灭之前设置DIM flag
					if (now < nextTimeout) {
						mUserActivitySummary |= USER_ACTIVITY_SCREEN_DIM;
					}
				}
			}
			if (mUserActivitySummary == 0
					&& mLastUserActivityTimeNoChangeLights >= mLastWakeTime) {
				nextTimeout = mLastUserActivityTimeNoChangeLights + screenOffTimeout;
				if (now < nextTimeout
						&& mDisplayPowerRequest.screenState
								!= DisplayPowerRequest.SCREEN_STATE_OFF) {
					mUserActivitySummary = mDisplayPowerRequest.screenState
							== DisplayPowerRequest.SCREEN_STATE_BRIGHT ?
							USER_ACTIVITY_SCREEN_BRIGHT : USER_ACTIVITY_SCREEN_DIM;
				}
			}
			// mUserActivitySummary发生了改变
			if (mUserActivitySummary != 0) {
				Message msg = mHandler.obtainMessage(MSG_USER_ACTIVITY_TIMEOUT);
				Slog.i(TAG, "updateUserActivitySummaryLocked, send MSG_USER_ACTIVITY_TIMEOUT");
				msg.setAsynchronous(true);
				mHandler.sendMessageAtTime(msg, nextTimeout);
			}
		} else {
			mUserActivitySummary = 0;
		}
	}
}

MSG_USER_ACTIVITY_TIMEOUT事件处理：

private final class PowerManagerHandler extends Handler {
	@Override
	public void handleMessage(Message msg) {
		switch (msg.what) {
		case MSG_USER_ACTIVITY_TIMEOUT:
			handleUserActivityTimeout();
			break;
	}
}

/**
 * Called when a user activity timeout has occurred.
 * Simply indicates that something about user activity has changed so that the new
 * state can be recomputed when the power state is updated.
 */
private void handleUserActivityTimeout() { // runs on handler thread
	mDirty |= DIRTY_USER_ACTIVITY;
	updatePowerStateLocked();
}

三、PowerManagerService中休眠锁的获取/释放

这部分代码清晰，直接看下：

private void updatePowerStateLocked() {
	if (!mSystemReady || mDirty == 0) {
		return;
	}
	// Phase 0: Basic state updates.

	// Phase 1: Update wakefulness.
	
	// Phase 2: Update dreams and display power state.
	
	// Phase 3: Send notifications, if needed.
	
	// Phase 4: Update suspend blocker.
	// Because we might release the last suspend blocker here, we need to make sure
	// we finished everything else first!
	updateSuspendBlockerLocked();
}

/**
 * Updates the suspend blocker that keeps the CPU alive.
 */
private void updateSuspendBlockerLocked() {
	final boolean needWakeLockSuspendBlocker = ((mWakeLockSummary & WAKE_LOCK_CPU) != 0);
	final boolean needDisplaySuspendBlocker = needDisplaySuspendBlocker();

	// First acquire suspend blockers if needed.
	if (needWakeLockSuspendBlocker && !mHoldingWakeLockSuspendBlocker) {
		mWakeLockSuspendBlocker.acquire();
		mHoldingWakeLockSuspendBlocker = true;
	}
	if (needDisplaySuspendBlocker && !mHoldingDisplaySuspendBlocker) {
		mDisplaySuspendBlocker.acquire();
		mHoldingDisplaySuspendBlocker = true;
	}

	// Then release suspend blockers if needed.
	if (!needWakeLockSuspendBlocker && mHoldingWakeLockSuspendBlocker) {
		mWakeLockSuspendBlocker.release();
		mHoldingWakeLockSuspendBlocker = false;
	}
	if (!needDisplaySuspendBlocker && mHoldingDisplaySuspendBlocker) {
		mDisplaySuspendBlocker.release();
		mHoldingDisplaySuspendBlocker = false;
	}
}

private final class SuspendBlockerImpl implements SuspendBlocker {
	private final String mName;
	private int mReferenceCount;

	public SuspendBlockerImpl(String name) {
		mName = name;
	}
	
	@Override
	public void acquire() {
		synchronized (this) {
			mReferenceCount += 1;
			if (mReferenceCount == 1) {
				nativeAcquireSuspendBlocker(mName);
			}
		}
	}

	@Override
	public void release() {
		synchronized (this) {
			mReferenceCount -= 1;
			if (mReferenceCount == 0) {

				nativeReleaseSuspendBlocker(mName);
			}
		}
	}
}

休眠锁的获取和释放，最终通过JNI方式读写/sys/power/wake_lock、/sys/power/wake_unlock：

// 1、JNI接口
com_android_server_power_PowerManagerService.cpp (frameworks\base\services\jni)
static void nativeAcquireSuspendBlocker(JNIEnv *env, jclass clazz, jstring nameStr) {
    ScopedUtfChars name(env, nameStr);
    acquire_wake_lock(PARTIAL_WAKE_LOCK, name.c_str());
}

// 2、定义要操作的文件
power.c (hardware\libhardware_legacy\power)
const char * const NEW_PATHS[] = {
    "/sys/power/wake_lock",
    "/sys/power/wake_unlock",
};

// 3、初始化设备节点
static inline void initialize_fds(void)
{
    if (g_initialized == 0) {
        if(open_file_descriptors(NEW_PATHS) < 0)
            open_file_descriptors(OLD_PATHS);
        g_initialized = 1;
    }
}

static int open_file_descriptors(const char * const paths[])
{
    int i;
    for (i=0; i