高通平台软件watchdog和ANR触发memory dump讲解

有时，当软件监视程序或ANR跟踪没有给出哪个组件持有锁的指示时，因为其他哪些线程被阻塞或内核端被阻塞就会使设备崩溃，以上这些问题只能通过memory dump进行分析.

解决方法：

软件 watchdog 触发 memory dump.

请设置persist property"persist.sys.crashOnWatchdog"为true ， 一旦发生看门狗，就会触发memory dump。 

Command: adb shell setprop persist.sys.crashOnWatchdog true
[Related code snippets]
/frameworks/base/services/core/java/com/android/server/Watchdog.java
@Override
public void run() {
boolean waitedHalf = false;
while (true) {
......
boolean crashOnWatchdog = SystemProperties.getBoolean("persist.sys.crashOnWatchdog", false)
;
if (crashOnWatchdog) {
doSysRq('w');
doSysRq('l');
// wait until the above blocked threads be dumped into kernel log
SystemClock.sleep(3000);
// now try to crash the target
doSysRq('c');
}

2. ANR 触发 memory dump, please 添加如下  patch.

[Android S patch]
--
diff --git a/services/core/java/com/android/serve