我们遇到Android系统开机界面(bootanimation)后，系统没法运行起来的问题，
系统一直出现 waiting for ...日志
似乎在等什么服务启动
因此怀疑system server 被block了
调试方法如下：
1. adb shell mkdir /data/anr/
2. adb shell ps | grep system_server
system 1138 234 908376 39440 ffffffff 40061a54 S system_server
3. adb shell kill -3 1138
4. adb shell pull /data/anr/trace.txt
----- pid 1138 at 2014-01-01 08:40:42 -----
Cmd line: system_server
JNI: CheckJNI is off; workarounds are off; pins=1; globals=289
DALVIK THREADS:
(mutexes: tll=0 tsl=0 tscl=0 ghl=0)
"main" prio=5 tid=1 MONITOR
| group="main" sCount=1 dsCount=0 obj=0x4159ee58 self=0x414be920
| sysTid=1138 nice=-2 sched=0/0 cgrp=apps handle=1073963348
| state=S schedstat=( 6367457522 242583118 5270 ) utm=595 stm=41 core=0
at com.android.server.am.ActivityManagerService.registerReceiver(ActivityManagerService.java:~13106)
- waiting to lock <0x41965278> (a com.android.server.am.ActivityManagerService) held by tid=27 (InputDispatcher)
at android.app.ContextImpl.registerReceiverInternal(ContextImpl.java:1458)
at android.app.ContextImpl.registerReceiverAsUser(ContextImpl.java:1433)
at android.content.pm.RegisteredServicesCache.<init>(RegisteredServicesCache.java:134)
at android.content.SyncAdaptersCache.<init>(SyncAdaptersCache.java:43)
at com.android.server.content.SyncManager.<init>(SyncManager.java:399)
at com.android.server.content.ContentService.getSyncManager(ContentService.java:75)
at com.android.server.content.ContentService.notifyChange(ContentService.java:283)
at android.content.ContentResolver.notifyChange(ContentResolver.java:1621)
at com.android.providers.settings.SettingsProvider.sendNotify(SettingsProvider.java:262)
at com.android.providers.settings.SettingsProvider.insertForUser(SettingsProvider.java:941)
at com.android.providers.settings.SettingsProvider.call(SettingsProvider.java:645)
at android.content.ContentProvider$Transport.call(ContentProvider.java:325)
at android.provider.Settings$NameValueCache.putStringForUser(Settings.java:903)
at android.provider.Settings$System.putStringForUser(Settings.java:1169)
at android.provider.Settings$System.putIntForUser(Settings.java:1274)
at android.provider.Settings$System.putInt(Settings.java:1268)
可以清晰的看到调用堆栈，是谁阻塞了system_server 的运行。