Android PowerManager.WakeLock使用小结

frameworks/base/core/java/android/os/PowerManager.java

WakeLock获取方法：

申请权限：

<uses-permission android:name="android.permission.WAKE_LOCK" />

1.acquire()--普通锁，需要手动release()，否则无法进入休眠

public void acquire() {
synchronized (mToken) {
acquireLocked();
}
}

2.acquire(long timeout)--超时锁，超过参数中的时间系统自动释放

public void acquire(long timeout) {
synchronized (mToken) {
acquireLocked();
mHandler.postDelayed(mReleaser, timeout);
}
}

WakeLock是否已经acquire()：

public boolean isHeld() {
synchronized (mToken) {
return mHeld;
}
}

WakeLock类型：

/** CPU：保持运转 屏幕：可以关闭 键盘灯：可以关闭 **/
public static final int PARTIAL_WAKE_LOCK = 0x00000001;

/** CPU：保持运转 屏幕：保持显示但可以是暗的 键盘灯：关闭 **/
@Deprecated
public static final int SCREEN_DIM_WAKE_LOCK = 0x00000006;

/** CPU：保持运转 屏幕：保持高亮 键盘灯：关闭 **/
@Deprecated
public static final int SCREEN_BRIGHT_WAKE_LOCK = 0x0000000a;

/** CPU：保持运转 屏幕：保持高亮 键盘灯：点亮 **/
@Deprecated
public static final int FULL_WAKE_LOCK = 0x0000001a;

注意事项：
1.普通锁：就是一点，不用时，必需及时release掉。

2.超时锁：这个看似很傻瓜，其实也有陷阱，如下两种方式：

private void acquireWakeLock1() {
wakeLock = powerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
this.getClass().getCanonicalName());
wakeLock.acquire(90 * 1000);
}

private void acquireWakeLock2() {
if(wakeLock == null){
wakeLock = powerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
this.getClass().getCanonicalName());
}
wakeLock.acquire(90 * 1000);
}

方法1和方法2在如下情形下加锁时间的长短不同：

时间	acquireWakeLock1	acquireWakeLock2
00:00:00	run	run
00:01:00	run	run
00:01:30		release
00:02:30	release	goTosleep()
... ...	goTosleep()

对于acquireWakeLock1()，每次执行都会重新锁定90s；

而对于acquireWakeLock2()，如果执行第二次的时候isHeld()为true，则进行第一次的锁定。

附：WakeLock未释放造成无法进入深度休眠（Suspend）时该如何定位：

抓取Log，搜索PowerManagerService关于WakeLock的打印，注意类似以下片段：

12-23 21:31:26.986 634 675 I PowerManagerService: Going to sleep by user request...
12-23 21:31:26.986 634 675 D PowerManagerNotifier: onGoToSleepStarted
12-23 21:31:26.986 634 675 D PowerManagerService: wakelock list dump: mLocks.size=2:
12-23 21:31:26.986 634 675 D PowerManagerService: No.0: PARTIAL_WAKE_LOCK 'com.zms.wakelock.WakeLockTestService'activated(flags=1, uid=10017, pid=787) total=2515481ms)
12-23 21:31:26.986 634 675 D PowerManagerService: No.1: PARTIAL_WAKE_LOCK 'AudioMix'activated(flags=1, uid=1013, pid=132) total=3306ms)
Log中可以看到有两个锁一直没有释放，所以无法进入深度休眠。

PowerManagerService有个ArrayList管理所有的WakeLock，为空时才能进入深度休眠：

// Table of all wake locks acquired by applications.
private final ArrayList<WakeLock> mWakeLocks = new ArrayList<WakeLock>();

以下是Log中打印处涉及的源码，打印出了WakeLock的类型，申请者的TAG，UID和PID，以及该锁acquire的时长，方便开发者定位检查：
private void dumpWakeLockLocked() {
final int numWakeLocks = mWakeLocks.size();
if (numWakeLocks > 0) {
Slog.d(TAG, "wakelock list dump: mLocks.size=" + numWakeLocks + ":");
} else {
return;
}

for (int i = 0; i < numWakeLocks; i++) {
final WakeLock wakeLock = mWakeLocks.get(i);
String type = "";

switch (wakeLock.mFlags & PowerManager.WAKE_LOCK_LEVEL_MASK) {
case PowerManager.PARTIAL_WAKE_LOCK:
type = "PARTIAL_WAKE_LOCK";
break;
case PowerManager.FULL_WAKE_LOCK:
type = "FULL_WAKE_LOCK";
break;
case PowerManager.SCREEN_BRIGHT_WAKE_LOCK:
type = "SCREEN_BRIGHT_WAKE_LOCK";
break;
case PowerManager.SCREEN_DIM_WAKE_LOCK:
type = "SCREEN_DIM_WAKE_LOCK";
break;
case PowerManager.PROXIMITY_SCREEN_OFF_WAKE_LOCK:
type = "PROXIMITY_SCREEN_OFF_WAKE_LOCK";
break;
}
long total_time = SystemClock.uptimeMillis() - wakeLock.mActiveSince;
Slog.d(TAG, "No." + i + ": " + type + " '" + wakeLock.mTag + "'"
+ "activated" + "(flags=" + wakeLock.mFlags
+ ", uid=" + wakeLock.mOwnerUid + ", pid=" + wakeLock.mOwnerPid + ")" + " total=" + total_time + "ms)");
}
}