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Android powermanger wakelock

上传者： yangxingda188 | 上传时间： 2024-07-13 12:01:59 | 文件大小： 1.36MB | 文件类型： ZIP
author：杨兴达； 邮箱：yangxingda1988@163.com 电话：180 1018 0585 Android 电源管理 -- wakelock机制，通过控制wakelock 实现保持pad 禁止休眠状态； Wake Lock是一种锁的机制, 只要有人拿着这个锁,系统就无法进入休眠, 可以被用户态程序和内核获得. 这个锁可以是有超时的 或者 是没有超时的, 超时的锁会在时间过去以后自动解锁。如果没有锁了或者超时了, 内核就会启动休眠的那套机制来进入休眠. PowerManager.WakeLock 有加锁和解锁两种状态，加锁的方式有两种： 第一种是永久的锁住，这样的锁除非显式的放开，否则是不会解锁的，所以这种锁用起来要非常的小心。 第二种锁是超时锁，这种锁会在锁住后一段时间解锁。 在创建了 PowerManager.WakeLock 后，有两种机制，第一种是不计数锁机制，另一种是计数锁机制。可以通过 setReferenceCounted(boolean value) 来指定，一般默认为计数机制。这两种机制的区别在于，前者无论 acquire() 了多少次，只要通过一次 release()即可解锁。而后者正真解锁是在（ --count == 0 ）的时候，同样当 (count == 0) 的时候才会去申请加锁。所以 PowerManager.WakeLock 的计数机制并不是正真意义上的对每次请求进行申请／释放每一把锁，它只是对同一把锁被申请／释放的次数进行了统计，然后再去操作。 源码 位置：frameworks/base/core/java/android/os/PowerManager.java ++++++++++++++++++++++++ 讲述 应用层 申请的锁 怎么传到kernel下面的，来理解 整个wakelock的框架。 比如android跑起来之后 在 /sys/power/wake_lock 下面的PowerManagerService 的生成过程。 1).应用程序申请锁 Android 提供了现成 android.os.PowerManager 类 , 类中 提供newWakeLock(int flags, String tag)方法 来取得 应用层的锁， 此函数的定义 frameworks/base/core/java/android/os/PowerManager.java 应用程序 在申请wake_lock时 都会有调用以下 部分。 实例： PowerManager pm = (PowerManager)getSystemService(Context.POWER_SERVICE); PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.SCREEN_DIM_WAKE_LOCK, “MyTag”); wl.acquire();//申请锁，这里会调用PowerManagerService里面acquireWakeLock() *********************** wl.release(); //释放锁，显示的释放锁，如果申请的锁不在此释放，系统就不会进入休眠。 ====================================== 2). frameworks层 /frameworks/base/services/java/com/android/server/PowerManagerService.java这个类是来管理 所有的应用程序 申请的wakelock。比如音视、频播放器、camera等申请的wakelock 都是通过这个类来 管理的。 static final String PARTIAL_NAME ="PowerManagerService" nativeAcquireWakeLock(PARTIAL_WAKE_LOCK_ID, PARTIAL_NAME); 上面 这个函数调用Power类 里面的 acquireWakeLock()，此时的PARTIAL_NAME作为参数传递到底层去。 public static native void nativeAcquireWakeLock(int lock, String id); 注：在PowerManagerService 类中没有实现nativeAcquireWakeLock，其实现体在 frameworks/base/core/jni/android_os_Power.cpp中，所以nativeAcquireWakeLock()方法时会调用JNI下的实现方法。 3).JNI层的实现 路径：frameworks/base/core/jni/android_os_Power.cpp // static void acquireWakeLock(JNIEnv *env, jobject clazz, jint lock, jstring idObj) { ************** const char *id = env->GetStringUTFChars(idObj, NULL); acquire_wake_lock(lock, id); env->ReleaseStringUTFChars(idObj, id); } 注：在acquireWakeLock()中调用了 路径下hardware/libhardware_legacy/power/power.c下面的acquire_wake_lock(lock, id) 4).与kernel层的交互 在power.c下的acquire_wake_lock(lock, id)函数如下： int acquire_wake_lock(int lock, const char* id) { ************** return write(fd, id, strlen(id)); } 注： fd就是文件描述符，在此 表示”/sys/power/wake_lock” id就是从PowerManagerService类中传下来的参数即：PARTIAL_NAME = "PowerManagerService" 到此 就是通过 文件系统 来与kernel层 交互的地方。 +++++++++++++++++++++++++++++++++++++++++++++++++++++ PowerManager类被应用程序调用，控制电源设备状态切换: PowerManager类对外有三个接口函数: 1、void goToSleep(long time); //强制设备进入Sleep状态 Note:在应用层调用该函数, 应用需要 在 源码下编译，用系统签名，否则 调用 此函数 出错； 2、newWakeLock(int flags, String tag);//取得相应层次的锁 flags参数说明: PARTIAL_WAKE_LOCK :保持CPU 运转，屏幕和键盘灯是关闭的。 SCREEN_DIM_WAKE_LOCK ：保持CPU 运转，允许保持屏幕显示但有可能是灰的，关闭键盘灯 SCREEN_BRIGHT_WAKE_LOCK ：保持CPU 运转，保持屏幕高亮显示，关闭键盘灯 FULL_WAKE_LOCK ：保持CPU 运转，保持屏幕高亮显示，键盘灯也保持亮度 ACQUIRE_CAUSES_WAKEUP: 一旦有请求锁时，强制打开Screen和keyboard light ON_AFTER_RELEASE: 在释放锁时reset activity timer Note: 如果申请了partial wakelock,那么即使按Power键,系统也不会进Sleep,如Music播放时 如果申请了其它的wakelocks,按Power键,系统还是会进Sleep 3、void userActivity(long when, boolean noChangeLights);//User activity事件发生,设备会被切换到Full on的状态,同时Reset Screen off timer. PowerManager和WakeLock的操作步骤 PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);通过 Context.getSystemService().方法获取PowerManager实例。 然后通过PowerManager的newWakeLock ((int flags, String tag)来生成WakeLock实例。int Flags指示要获取哪种WakeLock，不同的Lock对cpu 、屏幕、键盘灯有不同影响。 获取WakeLock实例后通过acquire()获取相应的锁，然后进行其他操作，最后使用release()释放（释放是必须的）。 Note: 1. 在使用以上函数的应用程序中,必须在其Manifest.xml文件中加入下面的权限: 2. 所有的锁必须成对的使用, 如果申请了而没有及时释放，会造成系统故障。如申请了partial wakelock,而没有及时释放, 那系统就永远进不了Sleep模式.

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