Explanation of memory dump triggered by software watchdog and anr

Sometimes , When a software monitor or ANR When the trace does not give an indication which component holds the lock , Because which other threads are blocked or the kernel side is blocked, the device will crash , These questions can only be answered through memory dump Analyze .

resolvent ：

Software watchdog Trigger memory dump.

Please set up persist property"persist.sys.crashOnWatchdog" by true ,  In case of a watchdog , It will trigger 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 Trigger memory dump, please Add the following   patch.

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