Bug - WatchDog timout

• RootCause
• watchdog will schedule a check to acquire the lock, if can't get the lock then report timeout.

W Watchdog: *** WATCHDOG KILLING SYSTEM PROCESS: Blocked in monitor com.android.server.am.ActivityManagerService on foreground thread (android.fg), Blocked in handler on ActivityManager (ActivityManager), Blocked in handler on WindowManager thread (WindowManager)
 W Watchdog: foreground thread stack trace:
 W Watchdog:     at com.android.server.am.ActivityManagerService.monitor(ActivityManagerService.java:16009)
.........
 W Watchdog: ActivityManager stack trace:
 W Watchdog:     at com.android.server.am.ActivityStack$ActivityStackHandler.handleMessage(ActivityStack.java:292)

•    Usually we can see it if deadlock, trace the traces.txt,  there is a deadlock b/w threads.

"Binder_C" prio=5 tid=58 MONITOR
  | group="main" sCount=1 dsCount=0 obj=0x425af1d0 self=0x732d34b0
  | sysTid=1171 nice=-8 sched=0/0 cgrp=apps handle=1932210896
  | state=S schedstat=( 3712885896 3165563645 19485 ) utm=285 stm=85 core=0
  at com.android.server.wm.WindowManagerService.moveTaskToTop(WindowManagerService.java:~4792)
  - waiting to lock <0x424aea70> (a java.util.HashMap) held by tid=57 (Binder_B)
......
"Binder_B" prio=5 tid=57 MONITOR
  | group="main" sCount=1 dsCount=0 obj=0x4279b7c8 self=0x6c452620
  | sysTid=1134 nice=0 sched=0/0 cgrp=apps handle=1816469512
  | state=S schedstat=( 5136093661 3481006328 21082 ) utm=419 stm=94 core=0
  at com.android.server.am.ActivityManagerService.broadcastIntent(ActivityManagerService.java:~13693)
  - waiting to lock <0x42033500> (a com.android.server.am.ActivityManagerService) held by tid=58 (Binder_C)

•     Check the source code, you can find below.

     * NOTE: Never call into methods that lock ActivityManagerService while holding this object.

*/
final HashMap<IBinder, WindowState> mWindowMap = new HashMap<IBinder, WindowState>();

Solution.

Process/Thread who cause the resource lock should rewrite the code to prevent the case like this.

Note about WatchDog

Service have to add itself to the monitor by Watchdog.getInstance().addMonitor(this) or addThread. Service also need to implement the monitor function to simply lock the service object itself.
If addMonitor, it will be added into the default foreground thread main checker. For others will create a new checker like UiThread, IoThread, Main looper.
WatchDog will query the lock and stop if timeout.