dvm_lock_sample解析

dvm_lock_sample:当某个线程等待lock的时间blocked超过阈值（比如：500ms）,则输出当前的持锁状态.

 dvm_lock_sample: [system_server,1,Binder_9,1500,ActivityManagerService.java,6403,-,1448,0]
说明：system_server: Binder_9,执行到ActivityManagerService.java的6403行代码,一直在等待AMS锁, "-"代表持锁的是同一个文件，

即该锁被同一文件的1448行代码所持有, 从而导致Binder_9线程被阻塞1500ms.
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dvm_lock_sample 会打印出系统主线程的一些主要方法耗费了多少时间
dvm_lock_sample:[system_server,1,Binder:1614_A,22,AlarmManagerService.java,1072,-,2496,4] 
（进程名,是否主线程1是0否,线程号,花费时间,文件名,申请锁行数，持锁文件名，持锁行数,采样频率）
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03-06 13:56:00.928  1160  1740 I dvm_lock_sample: [system_server,1,Binder:1160_6,22574,ActivityTaskManagerService.java,1850,void com.android.server.wm.ActivityTaskManagerService.activityTopResumedStateLost(android.os.IBinder),
TaskChangeNotificationController.java,351,void com.android.server.wm.TaskChangeNotificationController.forAllLocalListeners(com.android.server.wm.TaskChangeNotificationController$TaskStackConsumer, android.os.Message),100]

通过分析log，在13:56:00.927节点的时候，TaskChangeNotificationController.forAllLocalListeners()方法持有了WindowManagerGlobalLock锁导致ActivityTaskManagerService.activityTopResumedStateLost()方法一直在等待WindowManagerGlobalLock锁释放，等待时长为22.574 s

TaskChangeNotificationController.forAllLocalListeners

private void forAllLocalListeners(TaskStackConsumer callback, Message message) {
    synchronized (mServiceLock) {
        for (int i = mLocalTaskStackListeners.size() - 1; i >= 0; i--) {
            try {
                callback.accept(mLocalTaskStackListeners.get(i), message);
            } catch (RemoteException e) {
                // Never thrown since this is called locally.
            }
        }
    }
}

该方法中持有了WindowManagerGlobalLock锁，然后执行了for循环，执行callback回调