查看JAVA进程PID。
jps 命令用来查看所有 Java 进程，每一行就是一个 Java 进程信息。
jps 仅查找当前用户的 Java 进程，而不是当前系统中的所有进程，要显示其他用户的还只能用 ps 命令。
jps 常用参数
第一列的数字就是进程的 pid
Copy# michael @ Michael-MBP in ~ [16:37:59]
$ jps -v |grep Mybatis
8005 MybatisDemoApplication -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:53364,suspend=y,server=n -XX:TieredStopAtLevel=1 -Xverify:none -Dspring.output.ansi.enabled=always -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=53363 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -Djava.rmi.server.hostname=127.0.0.1 -Dspring.liveBeansView.mbeanDomain -Dspring.application.admin.enabled=true -javaagent:/Users/michael/Library/Caches/IntelliJIdea2018.2/captureAgent/debugger-agent.jar=file:/private/var/folders/m1/ydypchs901lffc5sms07mrp40000gn/T/capture.props -Dfile.encoding=UTF-8
jps 是比较常用的 Java 命令。使用 jps 可以查看当前有哪些 Java 进程处于运行状态。如果运行了一个 web 应用（使用Tomcat、jboss、jetty等启动）的时候，就可以使用 jps 查看启动情况。
有的时候我想知道这个应用的日志会输出到哪里，或者启动的时候使用了哪些javaagent，那么我可以使用 jps -v 查看进程的jvm参数情况。
参考原文：https://blog.csdn.net/yx0628/article/details/80958488
jinfo -flag initilHeapSize ${PID}查看某个JAVA进程中，JVM的参数值是什么。
jinfo -flag ${PID} 如果不加JVM参数的话，默认查看JVM中所有被修改过的值。
[root@admin ~]# jinfo --help
Usage:
jinfo [option] <pid>
(to connect to running process)
jinfo [option] <executable <core>
(to connect to a core file)
jinfo [option] [server_id@]<remote server IP or hostname>
(to connect to remote debug server)
where <option> is one of:
-flag <name> to print the value of the named VM flag
-flag [+|-]<name> to enable or disable the named VM flag
-flag <name>=<value> to set the named VM flag to the given value
-flags to print VM flags
-sysprops to print Java system properties
<no option> to print both of the above
-h | -help to print this help message
我们先用 jps 命令查到 PID ，然后可以通过 jinfo 来查看对应进程的参数信息：
[root@admin ~]# jps
43520 Test
35900 Jps
查看 JVM 参数：
[root@admin ~]# jinfo -flags 43520
Attaching to process ID 43520, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.45-b08
-Dfile.encoding=GBK
查看系统参数：
[root@admin ~]# jinfo -sysflags 43520
虚拟机的参数可以通过这个命令查看：
java -XX:+PrintFlagsFinal -version | grep manageable
除了通过启动脚本可以设置参数，PrintGC 默认是打开的，因此我们只需要打开 PrintGCDetails 参数。
jinfo -flag +PrintGC 43520
jinfo -flag +PrintGCDetails 43520
关闭 GC 日志的话同理：
jinfo -flag -PrintGC 43520
jinfo -flag -PrintGCDetails 43520
查看是否开启 GC 日志的打印：
jinfo -flag PrintGC 43520
jinfo -flag PrintGCDetails 43520
[root@admin ~]# jinfo -flag PrintGC 43520
-XX:-PrintGC
[root@admin ~]# jinfo -flag PrintGCDetails 43520
-XX:-PrintGCDetails
常用 JVM 参数：
-Xms：初始堆大小，默认为物理内存的1/64(<1GB)；默认(MinHeapFreeRatio参数可以调整)空余堆内存小于40%时，JVM就会增大堆直到-Xmx的最大限制
-Xmx：最大堆大小，默认(MaxHeapFreeRatio参数可以调整)空余堆内存大于70%时，JVM会减少堆直到 -Xms的最小限制
-Xmn：新生代的内存空间大小，注意：此处的大小是（eden+ 2 survivor space)。与jmap -heap中显示的New gen是不同的。整个堆大小=新生代大小 + 老生代大小 + 永久代大小。在保证堆大小不变的情况下，增大新生代后,将会减小老生代大小。此值对系统性能影响较大,Sun官方推荐配置为整个堆的3/8。
-XX:SurvivorRatio：新生代中Eden区域与Survivor区域的容量比值，默认值为8。两个Survivor区与一个Eden区的比值为2:8,一个Survivor区占整个年轻代的1/10。
-Xss：每个线程的堆栈大小。JDK5.0以后每个线程堆栈大小为1M,以前每个线程堆栈大小为256K。应根据应用的线程所需内存大小进行适当调整。在相同物理内存下,减小这个值能生成更多的线程。但是操作系统对一个进程内的线程数还是有限制的，不能无限生成，经验值在3000~5000左右。一般小的应用， 如果栈不是很深， 应该是128k够用的，大的应用建议使用256k。这个选项对性能影响比较大，需要严格的测试。和threadstacksize选项解释很类似,官方文档似乎没有解释,在论坛中有这样一句话:"-Xss is translated in a VM flag named ThreadStackSize”一般设置这个值就可以了。
-XX:PermSize：设置永久代(perm gen)初始值。默认值为物理内存的1/64。
-XX:MaxPermSize：设置持久代最大值。物理内存的1/4。
原文参考：https://blog.csdn.net/cockroach02/article/details/82670500
查看JVM中相关性能的信息。
jstat（Java Virtual machine Statistics Monitoring Tool）是从JDK1.5自带的一个轻量级小工具。它位于java/bin目录下，主要利用JVM内建的指令对Java虚拟机的资源和性能进行实时的监控。
类装载信息：jstat -class ${PID}
举例：jstat -class ${PID} ${几秒内打印一次} ${打印10次} = jstat -class ${PID} 1000 10。打印出过去10秒类加载的数据。
GC相关的情况：jstat -gc ${PID}
举例：jstat -gc ${PID} ${几秒内打印一次} ${打印10次} = jstat -gc ${PID} 1000 10。打印出过去10秒GC的数据。
参数说明：
C:UsersAdministrator>jstat -help
Usage: jstat -help|-options
jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]
Definitions:
<option> An option reported by the -options option
<vmid> Virtual Machine Identifier. A vmid takes the following form:
<lvmid>[@<hostname>[:<port>]]
Where <lvmid> is the local vm identifier for the target
Java virtual machine, typically a process id; <hostname> is
the name of the host running the target Java virtual machine;
and <port> is the port number for the rmiregistry on the
target host. See the jvmstat documentation for a more complete
description of the Virtual Machine Identifier.
<lines> Number of samples between header lines.
<interval> Sampling interval. The following forms are allowed:
<n>["ms"|"s"]
Where <n> is an integer and the suffix specifies the units as
milliseconds("ms") or seconds("s"). The default units are "ms".
<count> Number of samples to take before terminating.
-J<flag> Pass <flag> directly to the runtime system.
由以上可知，jstat的命令的格式如下：
jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]
我们可以通过jstat -options查看可以支持的具体参数
C:UsersAdministrator>jstat -options
-class
-compiler
-gc
-gccapacity
-gccause
-gcmetacapacity
-gcnew
-gcnewcapacity
-gcold
-gcoldcapacity
-gcutil
-printcompilation
Option参数说明：
参数 说明 -class 类加载的行为统计 Displays statistics about the behavior of the class loader. -compiler HotSpt JIT编译器行为统计 Displays statistics about the behavior of the Java HotSpot VM Just-in-Time compiler. -gc 垃圾回收堆的行为统计。Displays statistics about the behavior of the garbage collected heap. -gccapacity 各个垃圾回收代容量(young,old,meta)和他们相应的空间统计。isplays statistics about the capacities of the generations and their corresponding spaces. -gccause 垃圾收集统计概述（同-gcutil）,附加最近两次垃圾回收事件的原因。Displays a summary about garbage collection statistics (same as -gcutil), with the cause of the last and current (when applicable) garbage collection events. -gcmetacapacity 统计元空间使用情况 Displays statistics about the sizes of the metaspace. -gcnew 显示新生代统计信息 Displays statistics of the behavior of the new generation. -gcnewcapacity 统计新生代及内存使用情况 Displays statistics about the sizes of the new generations and its corresponding spaces. -gcold 统计老年代和元空间使用情况 Displays statistics about the behavior of the old generation and metaspace statistics. -gcoldcapacity 统计老年代内存使用情况 Displays statistics about the sizes of the old generation. -gcutil 显示各个各代内存使用百分比 Displays a summary about garbage collection statistics. -printcompilation Hotspot方法编译统计情况 Displays Java HotSpot VM compilation method statistics.
使用示例：
jstat -class ： 类加载的行为统计
C:UsersAdministrator>jstat -class 2284
Loaded Bytes Unloaded Bytes Time
30116 75021.8 26 51.4 86.72
jstat -compiler ：HotSpt JIT编译器行为统计
C:UsersAdministrator>jstat -compiler 2284
Compiled Failed Invalid Time FailedType FailedMethod
21247 8 0 189.38 1 com/fr/third/alibaba/druid/pool/DruidDataSource shrink
jstat -gc：垃圾回收堆的行为统计
C:UsersAdministrator>jstat -gc 2284
S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT GCT
104832.0 104832.0 0.0 0.0 838912.0 600103.2 1048576.0 565828.4 238672.0 232272.3 22392.0 21028.5 59 4.898 11 6.323 11.221
jstat -gccapacity ： 各个回收区内存情况
C:UsersAdministrator>jstat -gccapacity 2284
NGCMN NGCMX NGC S0C S1C EC OGCMN OGCMX OGC OC MCMN MCMX MC CCSMN CCSMX CCSC YGC FGC
1048576.0 1048576.0 1048576.0 104832.0 104832.0 838912.0 1048576.0 3145728.0 1048576.0 1048576.0 0.0 1265664.0 238672.0 0.0 1048576.0 22392.0
59 11
jstat -gccause ：垃圾收集统计概述
C:UsersAdministrator>jstat -gccause 2284
S0 S1 E O M CCS YGC YGCT FGC FGCT GCT LGCC GCC
0.00 0.00 91.90 53.96 97.32 93.91 59 4.898 11 6.323 11.221 System.gc() No GC
6 . gc -gcmetacapacity ：元空间使用情况
C:UsersAdministrator>jstat -gcmetacapacity 2284
MCMN MCMX MC CCSMN CCSMX CCSC YGC FGC FGCT GCT
0.0 1265664.0 238672.0 0.0 1048576.0 22392.0 59 11 6.323 11.221
7 . jstat -gcnew ： 显示新生代统计信息
C:UsersAdministrator>jstat -gcnew 2284
S0C S1C S0U S1U TT MTT DSS EC EU YGC YGCT
104832.0 104832.0 46710.2 0.0 6 6 52416.0 838912.0 22526.9 60 4.972
8 . jstat -gcnewcapacity ： 统计新生代及内存使用情况
C:UsersAdministrator>jstat -gcnewcapacity 2284
NGCMN NGCMX NGC S0CMX S0C S1CMX S1C ECMX EC YGC FGC
1048576.0 1048576.0 1048576.0 104832.0 104832.0 104832.0 104832.0 838912.0 838912.0 60 11
9 . jstat -gcold ： 统计老年代和元空间使用情况
C:UsersAdministrator>jstat -gcold 2284
MC MU CCSC CCSU OC OU YGC FGC FGCT GCT
251088.0 244521.5 23544.0 22058.7 1048576.0 565828.4 60 11 6.323 11.295
10 . jstat -gcoldcapacity ： 统计老年代内存使用情况
C:UsersAdministrator>jstat -gcoldcapacity 2284
OGCMN OGCMX OGC OC YGC FGC FGCT GCT
1048576.0 3145728.0 1048576.0 1048576.0 60 11 6.323 11.295
11 . jstat -gcutil ： 垃圾回收统计
C:UsersAdministrator>jstat -gcutil 2284
S0 S1 E O M CCS YGC YGCT FGC FGCT GCT
44.56 0.00 9.85 53.96 97.38 93.69 60 4.972 11 6.323 11.295
12 . jstat -printcompilation ： Hotspot方法编译统计情况
C:UsersAdministrator>jstat -printcompilation 2284
Compiled Size Type Method
21538 150 1 java/util/Collections reverse
参考：
jstat：https://docs.oracle.com/javase/8/docs/technotes/tools/unix/jstat.html jstat命令使用：https://www.cnblogs.com/lizhonghua34/p/7307139.html JVM调优命令-jstat：https://www.cnblogs.com/myna/p/7567769.html
参考原文：https://www.jianshu.com/p/8d5782bc596e
查看JAVA进程当中，线程内容。
jstack用法
/opt/java8/bin/jstack
Usage:
jstack [-l] <pid>
(to connect to running process) 连接活动线程
jstack -F [-m] [-l] <pid>
(to connect to a hung process) 连接阻塞线程
jstack [-m] [-l] <executable> <core>
(to connect to a core file) 连接dump的文件
jstack [-m] [-l] [server_id@]<remote server IP or hostname>
(to connect to a remote debug server) 连接远程服务器
Options:
-F to force a thread dump. Use when jstack <pid> does not respond (process is hung)
-m to print both java and native frames (mixed mode)
-l long listing. Prints additional information about locks
-h or -help to print this help message
jstack查看输出
/opt/java8/bin/jstack -l 28367
2019-06-25 15:04:46
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.77-b03 mixed mode):
"Attach Listener" #453 daemon prio=9 os_prio=0 tid=0x00007f9f94001000 nid=0xf30 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
Locked ownable synchronizers:
- None
"grpc-default-executor-263" #452 daemon prio=5 os_prio=0 tid=0x00007f9f4c01f800 nid=0x9aa waiting on condition [0x00007f9f398bd000]
java.lang.Thread.State: TIMED_WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00000007400243f0> (a java.util.concurrent.SynchronousQueue$TransferStack)
at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:460)
at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:362)
at java.util.concurrent.SynchronousQueue.poll(SynchronousQueue.java:941)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1066)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Locked ownable synchronizers:
- None
"http-bio-8080-exec-10" #235 daemon prio=5 os_prio=0 tid=0x0000000001bcc800 nid=0x3c13 waiting on condition [0x00007f9f384a9000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x0000000743d26638> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
at org.Apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:104)
at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:32)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
Locked ownable synchronizers:
- None
jstack统计线程数
/opt/java8/bin/jstack -l 28367 | grep 'java.lang.Thread.State' | wc -l
jstack检测死锁
死锁代码
public class DeathLock {
private static Lock lock1 = new ReentrantLock();
private static Lock lock2 = new ReentrantLock();
public static void deathLock() {
Thread t1 = new Thread() {
@Override
public void run() {
try {
lock1.lock();
TimeUnit.SECONDS.sleep(1);
lock2.lock();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
Thread t2 = new Thread() {
@Override
public void run() {
try {
lock2.lock();
TimeUnit.SECONDS.sleep(1);
lock1.lock();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
t1.setName("thread1");
t2.setName("thread2");
t1.start();
t2.start();
}
public static void main(String[] args) {
deathLock();
}
}
死锁日志
"mythread2" #12 prio=5 os_prio=0 tid=0x0000000058ef7800 nid=0x1ab4 waiting on condition [0x0000000059f8f000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00000000d602d610> (a java.util.concurrent.lock
s.ReentrantLock$NonfairSync)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInt
errupt(AbstractQueuedSynchronizer.java:836)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(A
bstractQueuedSynchronizer.java:870)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(Abstrac
tQueuedSynchronizer.java:1199)
at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLo
ck.java:209)
at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
at DeathLock$2.run(DeathLock.java:34)
Locked ownable synchronizers:
- <0x00000000d602d640> (a java.util.concurrent.locks.ReentrantLock$Nonfa
irSync)
"mythread1" #11 prio=5 os_prio=0 tid=0x0000000058ef7000 nid=0x3e68 waiting on condition [0x000000005947f000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00000000d602d640> (a java.util.concurrent.lock
s.ReentrantLock$NonfairSync)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInt
errupt(AbstractQueuedSynchronizer.java:836)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(A
bstractQueuedSynchronizer.java:870)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(Abstrac
tQueuedSynchronizer.java:1199)
at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLo
ck.java:209)
at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
at DeathLock$1.run(DeathLock.java:22)
Locked ownable synchronizers:
- <0x00000000d602d610> (a java.util.concurrent.locks.ReentrantLock$Nonfa
irSync)
Found one Java-level deadlock:
=============================
"mythread2":
waiting for ownable synchronizer 0x00000000d602d610, (a java.util.concurrent.l
ocks.ReentrantLock$NonfairSync),
which is held by "mythread1"
"mythread1":
waiting for ownable synchronizer 0x00000000d602d640, (a java.util.concurrent.l
ocks.ReentrantLock$NonfairSync),
which is held by "mythread2"
Java stack information for the threads listed above:
===================================================
"mythread2":
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00000000d602d610> (a java.util.concurrent.lock
s.ReentrantLock$NonfairSync)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInt
errupt(AbstractQueuedSynchronizer.java:836)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(A
bstractQueuedSynchronizer.java:870)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(Abstrac
tQueuedSynchronizer.java:1199)
at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLo
ck.java:209)
at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
at DeathLock$2.run(DeathLock.java:34)
"mythread1":
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00000000d602d640> (a java.util.concurrent.lock
s.ReentrantLock$NonfairSync)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInt
errupt(AbstractQueuedSynchronizer.java:836)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(A
bstractQueuedSynchronizer.java:870)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(Abstrac
tQueuedSynchronizer.java:1199)
at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLo
ck.java:209)
at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
at DeathLock$1.run(DeathLock.java:22)
Found 1 deadlock.
jstack检测cpu高
步骤一：查看cpu占用高进程
top
Mem: 16333644k total, 9472968k used, 6860676k free, 165616k buffers
Swap: 0k total, 0k used, 0k free, 6665292k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
17850 root 20 0 7588m 112m 11m S 100.7 0.7 47:53.80 java
1552 root 20 0 121m 13m 8524 S 0.7 0.1 14:37.75 AliYunDun
3581 root 20 0 9750m 2.0g 13m S 0.7 12.9 298:30.20 java
1 root 20 0 19360 1612 1308 S 0.0 0.0 0:00.81 init
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
3 root RT 0 0 0 0 S 0.0 0.0 0:00.14 migration/0
步骤二：查看cpu占用高线程
top -H -p 17850
top - 17:43:15 up 5 days, 7:31, 1 user, load average: 0.99, 0.97, 0.91
Tasks: 32 total, 1 running, 31 sleeping, 0 stopped, 0 zombie
Cpu(s): 3.7%us, 8.9%sy, 0.0%ni, 87.4%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 16333644k total, 9592504k used, 6741140k free, 165700k buffers
Swap: 0k total, 0k used, 0k free, 6781620k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
17880 root 20 0 7588m 112m 11m R 99.9 0.7 50:47.43 java
17856 root 20 0 7588m 112m 11m S 0.3 0.7 0:02.08 java
17850 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.00 java
17851 root 20 0 7588m 112m 11m S 0.0 0.7 0:00.23 java
17852 root 20 0 7588m 112m 11m S 0.0 0.7 0:02.09 java
17853 root 20 0 7588m 112m 11m S 0.0 0.7 0:02.12 java
17854 root 20 0 7588m 112m 11m S 0.0 0.7 0:02.07 java
步骤三：转换线程ID
printf "%xn" 17880
45d8
步骤四：定位cpu占用线程
jstack 17850|grep 45d8 -A 30
"pool-1-thread-11" #20 prio=5 os_prio=0 tid=0x00007fc860352800 nid=0x45d8 runnable [0x00007fc8417d2000]
java.lang.Thread.State: RUNNABLE
at java.io.FileOutputStream.writeBytes(Native Method)
at java.io.FileOutputStream.write(FileOutputStream.java:326)
at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:82)
at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:140)
- locked <0x00000006c6c2e708> (a java.io.BufferedOutputStream)
at java.io.PrintStream.write(PrintStream.java:482)
- locked <0x00000006c6c10178> (a java.io.PrintStream)
at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:221)
at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:291)
at sun.nio.cs.StreamEncoder.flushBuffer(StreamEncoder.java:104)
- locked <0x00000006c6c26620> (a java.io.OutputStreamWriter)
at java.io.OutputStreamWriter.flushBuffer(OutputStreamWriter.java:185)
at java.io.PrintStream.write(PrintStream.java:527)
- eliminated <0x00000006c6c10178> (a java.io.PrintStream)
at java.io.PrintStream.print(PrintStream.java:597)
at java.io.PrintStream.println(PrintStream.java:736)
- locked <0x00000006c6c10178> (a java.io.PrintStream)
at com.demo.guava.HardTask.call(HardTask.java:18)
at com.demo.guava.HardTask.call(HardTask.java:9)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
"pool-1-thread-10" #19 prio=5 os_prio=0 tid=0x00007fc860345000 nid=0x45d7 waiting on condition [0x00007fc8418d3000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00000006c6c14178> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
原文参考：https://www.jianshu.com/p/c52ffaca40a5
jmap是JDK自带的工具软件，主要用于打印指定Java进程(或核心文件、远程调试服务器)的共享对象内存映射或堆内存细节。可以使用jmap生成Heap Dump。在Java命令Java Dump和Java命令:Jstack中分别有关于Java Dump以及线程 Dump的介绍。 这篇文章主要介绍Java的堆Dump以及jmap命令
Java虚拟机的内存组成以及堆内存介绍 Java GC工作原理
常见内存错误：
outOfMemoryError 年老代内存不足。 outOfMemoryError:PermGen Space 永久代内存不足。 outOfMemoryError:GC overhead limit exceed 垃圾回收时间占用系统运行时间的98%或以上。
jmap 用法摘要
Usage:
jmap [option] <pid>
(to connect to running process)
jmap [option] <executable <core>
(to connect to a core file)
jmap [option] [server_id@]<remote server IP or hostname>
(to connect to remote debug server)
where <option> is one of:
<none> to print same info as Solaris pmap
-heap to print java heap summary
-histo[:live] to print histogram of java object heap; if the "live"
suboption is specified, only count live objects
-permstat to print permanent generation statistics
-finalizerinfo to print information on objects awaiting finalization
-dump:<dump-options> to dump java heap in hprof binary format
dump-options:
live dump only live objects; if not specified,
all objects in the heap are dumped.
format=b binary format
file=<file> dump heap to <file>
Example: jmap -dump:live,format=b,file=heap.bin <pid>
-F force. Use with -dump:<dump-options> <pid> or -histo
to force a heap dump or histogram when <pid> does not
respond. The "live" suboption is not supported
in this mode.
-h | -help to print this help message
-J<flag> to pass <flag> directly to the runtime system
参数：
选项:
示例：
查看java 堆（heap）使用情况,执行命令： jmap -heap 31846
Attaching to process ID 31846, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.71-b01
using thread-local object allocation.
Parallel GC with 4 thread(s)//GC 方式
Heap Configuration: //堆内存初始化配置
MinHeapFreeRatio = 0 //对应jvm启动参数-XX:MinHeapFreeRatio设置JVM堆最小空闲比率(default 40)
MaxHeapFreeRatio = 100 //对应jvm启动参数 -XX:MaxHeapFreeRatio设置JVM堆最大空闲比率(default 70)
MaxHeapSize = 2082471936 (1986.0MB) //对应jvm启动参数-XX:MaxHeapSize=设置JVM堆的最大大小
NewSize = 1310720 (1.25MB)//对应jvm启动参数-XX:NewSize=设置JVM堆的‘新生代’的默认大小
MaxNewSize = 17592186044415 MB//对应jvm启动参数-XX:MaxNewSize=设置JVM堆的‘新生代’的最大大小
OldSize = 5439488 (5.1875MB)//对应jvm启动参数-XX:OldSize=<value>:设置JVM堆的‘老生代’的大小
NewRatio = 2 //对应jvm启动参数-XX:NewRatio=:‘新生代’和‘老生代’的大小比率
SurvivorRatio = 8 //对应jvm启动参数-XX:SurvivorRatio=设置年轻代中Eden区与Survivor区的大小比值
PermSize = 21757952 (20.75MB) //对应jvm启动参数-XX:PermSize=<value>:设置JVM堆的‘永生代’的初始大小
MaxPermSize = 85983232 (82.0MB)//对应jvm启动参数-XX:MaxPermSize=<value>:设置JVM堆的‘永生代’的最大大小
G1HeapRegionSize = 0 (0.0MB)
Heap Usage://堆内存使用情况
PS Young Generation
Eden Space://Eden区内存分布
capacity = 33030144 (31.5MB)//Eden区总容量
used = 1524040 (1.4534378051757812MB) //Eden区已使用
free = 31506104 (30.04656219482422MB) //Eden区剩余容量
4.614088270399305% used //Eden区使用比率
From Space: //其中一个Survivor区的内存分布
capacity = 5242880 (5.0MB)
used = 0 (0.0MB)
free = 5242880 (5.0MB)
0.0% used
To Space: //另一个Survivor区的内存分布
capacity = 5242880 (5.0MB)
used = 0 (0.0MB)
free = 5242880 (5.0MB)
0.0% used
PS Old Generation //当前的Old区内存分布
capacity = 86507520 (82.5MB)
used = 0 (0.0MB)
free = 86507520 (82.5MB)
0.0% used
PS Perm Generation//当前的 “永生代” 内存分布
capacity = 22020096 (21.0MB)
used = 2496528 (2.3808746337890625MB)
free = 19523568 (18.619125366210938MB)
11.337498256138392% used
670 interned Strings occupying 43720 bytes.
查看堆内存(histogram)中的对象数量及大小。执行命令： jmap -histo 3331
num #instances #bytes class name
编号 个数 字节 类名
----------------------------------------------
1: 7 1322080 [I
2: 5603 722368 <methodKlass>
3: 5603 641944 <constMethodKlass>
4: 34022 544352 java.lang.Integer
5: 371 437208 <constantPoolKlass>
6: 336 270624 <constantPoolCacheKlass>
7: 371 253816 <instanceKlassKlass>
将内存使用的详细情况输出到文件，执行命令： jmap -dump:format=b,file=heapDump 6900
然后用jhat命令可以参看 jhat -port 5000 heapDump 在浏览器中访问：http://localhost:5000/ 查看详细信息
这个命令执行，JVM会将整个heap的信息dump写入到一个文件，heap如果比较大的话，就会导致这个过程比较耗时，并且执行的过程中为了保证dump的信息是可靠的，所以会暂停应用。
1.如果程序内存不足或者频繁GC，很有可能存在内存泄露情况，这时候就要借助Java堆Dump查看对象的情况。 2.要制作堆Dump可以直接使用jvm自带的jmap命令 3.可以先使用jmap -heap命令查看堆的使用情况，看一下各个堆空间的占用情况。 4.使用jmap -histo:[live]查看堆内存中的对象的情况。如果有大量对象在持续被引用，并没有被释放掉，那就产生了内存泄露，就要结合代码，把不用的对象释放掉。 5.也可以使用 jmap -dump:format=b,file=命令将堆信息保存到一个文件中，再借助jhat命令查看详细内容 6.在内存出现泄露、溢出或者其它前提条件下，建议多dump几次内存，把内存文件进行编号归档，便于后续内存整理分析。
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