Javacore和Heapdump生成和获取（1）

JavaCore文件

又称为ThreadDump，保存的是Java应用各线程在某一时刻的运行的位置，即JVM执行到哪一个类、哪一个方法、哪一个行上。
它是一个文本文件，打开后可以看到每一个线程的执行栈，以stack trace的显示。
通过对ThreadDump文件的分析可以得到应用是否“卡”在某一线程上，即在某一线程运行的时间太长。

HeapDump文件

二进制文件，它保存了某一时刻JVM堆中对象使用情况。
作用就是分析系统中是否存在内存溢出的情况。

JavaCore（ThreadDump）生成方法

方法1： Getting a Thread Dump Using jstack

In JDK 1.6 and higher, it is possible to get a thread dump on MS Windows using jstack.
Use PID via jps to check the PID of the currently running Java application process.
Use the extracted PID as the parameter of jstack to obtain a thread dump.

方法2： A Thread Dump Using jVisualVM

Generate a thread dump by using a program such as jVisualVM.
The task on the left indicates the list of currently running processes.
 Click on the process for which you want the information, 
and select the thread tab to check the thread information in real time.
 Click the Thread Dump button on the top right corner to get the thread dump file.

方法3：Generating in a Linux Terminal

Obtain the process pid by using ps -ef command to check the pid of the 
currently running Java process.
Use the extracted pid as the parameter of kill –SIGQUIT(3) to obtain a thread dump.

例如：

# 查询进程
# ps -ef | grep java  
user 3186 5872 0 18:40 pts/0 00:00:00 grep java  
root 7760 1 0 Oct27 ? 00:02:27 /usr/bin/java -server -XX:PermSize=64M -XX:MaxPermSize=128m  -classpath :/usr/local/tomcat8090/bin/bootstrap.jar  org.apache.catalina.startup.Bootstrap start  
# 执行kill命令
# kill -3 7760

ThreadDump文件格式

2018-10-09 11:27:02
Full thread dump Java HotSpot(TM) 64-Bit Server VM (24.80-b11 mixed mode):

"elasticsearch[Norman Osborn][management][T#2]" daemon prio=6 tid=0x0000000020d7f800 nid=0x434 waiting on condition [0x000000003446e000]
   java.lang.Thread.State: TIMED_WAITING (parking)
	at sun.misc.Unsafe.park(Native Method)
	- parking to wait for  <0x00000000ca2f0828> (a org.elasticsearch.common.util.concurrent.EsExecutors$ExecutorScalingQueue)
	at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:226)
	at java.util.concurrent.LinkedTransferQueue.awaitMatch(LinkedTransferQueue.java:731)
	at java.util.concurrent.LinkedTransferQueue.xfer(LinkedTransferQueue.java:644)
	at java.util.concurrent.LinkedTransferQueue.poll(LinkedTransferQueue.java:1145)
	at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1068)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:745)

   Locked ownable synchronizers:
	- None

"VM Thread" prio=10 tid=0x00000000099db000 nid=0xe64 runnable 

"GC task thread#0 (ParallelGC)" prio=6 tid=0x00000000025ce000 nid=0x1c18 runnable 

"GC task thread#1 (ParallelGC)" prio=6 tid=0x00000000025cf800 nid=0x10cc runnable 

"GC task thread#2 (ParallelGC)" prio=6 tid=0x00000000025d1800 nid=0xbcc runnable 

"GC task thread#3 (ParallelGC)" prio=6 tid=0x00000000025d3000 nid=0x1ee4 runnable 

"VM Periodic Task Thread" prio=10 tid=0x000000000b26b000 nid=0x194c waiting on condition 

JNI global references: 46038

HeapDump 生成方式

方法1：Using jVisualVM

方法2：jvm 参数

-XX:+HeapDumpOnOutOfMemoryError 
-XX:HeapDumpPath=/log/

最后

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