本文详细解析了JVM参数类型，包括标准参数、X参数和XX参数，并介绍了如何使用jps、jinfo、jmap、jstat和jstack等工具进行JVM运行时参数查看、内存溢出诊断、垃圾收集器信息获取及死锁检测，是Java开发者必备的JVM监控指南。
1、JVM的参数类型
1.1 标准参数：在各jdk版本中较稳定
-help-server -client-version -showversion-cp -classpath
1.2 X参数
1.2.1非标准化参数
1.2.2 -Xint：完全解释执行
调整为完全解释执行编译模式：
MacBook-Pro:dubbo-learn chuanzhou$ java -Xint -version
java version "1.8.0_161"
Java(TM) SE Runtime Environment (build 1.8.0_161-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.161-b12, interpreted mode) 1.2.3 -Xcomp：第一次使用就编译成本地代码
调整为编译执行编译模式：
MacBook-Pro:dubbo-learn chuanzhou$ java -Xcomp -version
java version "1.8.0_161"
Java(TM) SE Runtime Environment (build 1.8.0_161-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.161-b12, compiled mode) 1.2.4 -Xmixed：混合模式，JVM自己来决定是否编译成本地代码
MacBook-Pro:~ chuanzhou$ java -version
java version "1.8.0_161"
Java(TM) SE Runtime Environment (build 1.8.0_161-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.161-b12, mixed mode) 最后一行的mixed mode表明JVM默认使用的编译模式是混合模式
1.3 XX参数
使用最多的一种参数类型
1.3.1 Boolean类型
格式：-XX:[+/-] <name> 表示启用或者禁用name属性
比如：-XX:+UseConcMarkSweepGC 表示启用CMS垃圾回收器-XX:+UseG1GC 表示启用G1垃圾回收器
1.3.2 非Boolean类型
格式：-XX:<name> = <value> 表示name属性的值为value
比如：-XX:MaxGCPauseMillis=500 表示GC最大停顿时间是500毫秒-XX:GCTimeRatio=19 表示...
1.3.3 -Xmx -Xms
虽然1以X开头，但是不是X类型参数，而是XX类型的参数
- -Xmx等价于-XX:MaxHeapSize 表示最大堆内存大小，可使用
jinfo -flag MaxHeapSize 进程id查看，如下：
[root@izwz93osmk5vi5qwqyscxaz bin]# ps -ef|grep java
root 9723 1 0 4月24 ? 04:28:59 /usr/program/jdk1.8.0_72/jre/bin/java -Djava.util.logging.config.file=/opt/tomcat/apache-tomcat-8.0.50/conf/logging.properties -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -Djdk.tls.ephemeralDHKeySize=2048 -Djava.protocol.handler.pkgs=org.apache.catalina.webresources -Dignore.endorsed.dirs= -classpath /opt/tomcat/apache-tomcat-8.0.50/bin/bootstrap.jar:/opt/tomcat/apache-tomcat-8.0.50/bin/tomcat-juli.jar -Dcatalina.base=/opt/tomcat/apache-tomcat-8.0.50 -Dcatalina.home=/opt/tomcat/apache-tomcat-8.0.50 -Djava.io.tmpdir=/opt/tomcat/apache-tomcat-8.0.50/temp org.apache.catalina.startup.Bootstrap start root 20037 19984 0 20:53 pts/2 00:00:00 grep --color=auto java [root@izwz93osmk5vi5qwqyscxaz bin]# ./jinfo -flag MaxHeapSize 9723 -XX:MaxHeapSize=482344960 [root@izwz93osmk5vi5qwqyscxaz bin]# -
-Xms等价于-XX:InitalHeapSize 表示堆内存初始大小
-
-Xss等价于-XX:InitalStackSize 表示线程栈的初始大小，可以使用
jinfo -flag ThreadStackSize 进程id查看，如下：
[root@izwz93osmk5vi5qwqyscxaz bin]# ps -ef
[root@izwz93osmk5vi5qwqyscxaz bin]# ps -ef|grep java
root 9723 1 0 4月24 ? 04:28:59 /usr/program/jdk1.8.0_72/jre/bin/java -Djava.util.logging.config.file=/opt/tomcat/apache-tomcat-8.0.50/conf/logging.properties -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -Djdk.tls.ephemeralDHKeySize=2048 -Djava.protocol.handler.pkgs=org.apache.catalina.webresources -Dignore.endorsed.dirs= -classpath /opt/tomcat/apache-tomcat-8.0.50/bin/bootstrap.jar:/opt/tomcat/apache-tomcat-8.0.50/bin/tomcat-juli.jar -Dcatalina.base=/opt/tomcat/apache-tomcat-8.0.50 -Dcatalina.home=/opt/tomcat/apache-tomcat-8.0.50 -Djava.io.tmpdir=/opt/tomcat/apache-tomcat-8.0.50/temp org.apache.catalina.startup.Bootstrap start root 20037 19984 0 20:53 pts/2 00:00:00 grep --color=auto java [root@izwz93osmk5vi5qwqyscxaz bin]# ./jinfo -flag MaxHeapSize 9723 -XX:MaxHeapSize=482344960 [root@izwz93osmk5vi5qwqyscxaz bin]# ./jinfo -flag ThreadStackSize 9723 -XX:ThreadStackSize=1024 [root@izwz93osmk5vi5qwqyscxaz bin]# 2、JVM运行时参数查看
-XX:+printFlagsInitial查看JVM运行时初始值-XX:+printFlagsFinal查看JVM运行时最终值-XX:+UnlockExperimentalVMOptions解锁实验参数-XX:+UnlockDiagnosticVMOptions解锁诊断参数-XX:+PrintCommandLineFlags打印命令行参数
如查看JVM版本信息：java -XX:+PrintFlagsFinal -version > ~/version.txt
version.txt中部分参数：
[Global flags]
uintx AdaptiveSizeDecrementScaleFactor = 4 {product}
uintx AdaptiveSizeMajorGCDecayTimeScale = 10 {product}
uintx AdaptiveSizePausePolicy = 0 {product}
uintx AdaptiveSizePolicyCollectionCostMargin = 50 {product}
uintx AdaptiveSizePolicyInitializingSteps = 20 {product} uintx AdaptiveSizePolicyOutputInterval = 0 {product} uintx AdaptiveSizePolicyWeight = 10 {product} uintx AdaptiveSizeThroughPutPolicy = 0 {product} uintx AdaptiveTimeWeight = 25 {product} bool AdjustConcurrency = false {product} bool AggressiveOpts = false {product} bool C1ProfileVirtualCalls = true {C1 product} bool C1UpdateMethodData = true {C1 product} intx CICompilerCount := 2 {product} bool CICompilerCountPerCPU = true {product} bool CITime = false {product} bool CMSAbortSemantics = false {product} uintx CMSAbortablePrecleanMinWorkPerIteration = 100 {product} intx CMSAbortablePrecleanWaitMillis = 100 {manageable} uintx CMSBitMapYieldQuantum = 10485760 注：=表示默认值，=:表示修改后的值
jps：查看Java进程
[root@izwz93osmk5vi5qwqyscxaz bin]# ./jps
20160 Jps
9723 Bootstrap
[root@izwz93osmk5vi5qwqyscxaz bin]# ./jps -l
20170 sun.tools.jps.Jps 9723 org.apache.catalina.startup.Bootstrap [root@izwz93osmk5vi5qwqyscxaz bin]# 关于jps等命令的详解，可参考此文档https://docs.oracle.com/javase/8/docs/technotes/tools/unix/index.html
jinfo：查看指定Java进程运行时参数
如查看一个java进程id为9723的tomcat服务最大堆内存大小
[root@izwz93osmk5vi5qwqyscxaz bin]# ps -ef|grep java
root 9723 1 0 4月24 ? 04:29:03 /usr/program/jdk1.8.0_72/jre/bin/java -Djava.util.logging.config.file=/opt/tomcat/apache-tomcat-8.0.50/conf/logging.properties -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -Djdk.tls.ephemeralDHKeySize=2048 -Djava.protocol.handler.pkgs=org.apache.catalina.webresources -Dignore.endorsed.dirs= -classpath /opt/tomcat/apache-tomcat-8.0.50/bin/bootstrap.jar:/opt/tomcat/apache-tomcat-8.0.50/bin/tomcat-juli.jar -Dcatalina.base=/opt/tomcat/apache-tomcat-8.0.50 -Dcatalina.home=/opt/tomcat/apache-tomcat-8.0.50 -Djava.io.tmpdir=/opt/tomcat/apache-tomcat-8.0.50/temp org.apache.catalina.startup.Bootstrap start root 20187 20123 0 21:34 pts/2 00:00:00 grep --color=auto java [root@izwz93osmk5vi5qwqyscxaz bin]# ./jinfo -flag MaxHeapSize 9723 -XX:MaxHeapSize=482344960 [root@izwz93osmk5vi5qwqyscxaz bin]# 查看一个进程的所有运行时参数：
[root@izwz93osmk5vi5qwqyscxaz bin]# ./jinfo -flags 9732
Attaching to process ID 9732, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.72-b15
Non-default VM flags: -XX:CICompilerCount=2 -XX:InitialHeapSize=31457280 -XX:MaxHeapSize=482344960 -XX:MaxNewSize=160759808 -XX:MinHeapDeltaBytes=196608 -XX:NewSize=10485760 -XX:OldSize=20971520 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops Command line: -Djava.util.logging.config.file=/opt/tomcat/apache-tomcat-8.0.50/conf/logging.properties -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -Djdk.tls.ephemeralDHKeySize=2048 -Djava.protocol.handler.pkgs=org.apache.catalina.webresources -Dignore.endorsed.dirs= -Dcatalina.base=/opt/tomcat/apache-tomcat-8.0.50 -Dcatalina.home=/opt/tomcat/apache-tomcat-8.0.50 -Djava.io.tmpdir=/opt/tomcat/apache-tomcat-8.0.50/temp [root@izwz93osmk5vi5qwqyscxaz bin]# Non-default VM flags表示手动赋值过的参数，其中有些是tomcat设置的Command line：与Non-default VM flags
查看垃圾回收器信息
MacBook-Pro:dubbo-learn chuanzhou$ jinfo -flag UseConcMarkSweepGc 29159
no such flag 'UseConcMarkSweepGc'
MacBook-Pro:dubbo-learn chuanzhou$ jinfo -flag UseG1Gc 29159 no such flag 'UseG1Gc' MacBook-Pro:dubbo-learn chuanzhou$ jinfo -flag UseParallelGc 29159 no such flag 'UseParallelGc' 3、jstat查看虚拟机统计信息
3.1 类装载
格式：jstat -class 进程id 每隔多少毫秒 一共输出多少次
如：查看一个进程id为29159的java进程，每隔1s输出，一共输出10次
MacBook-Pro:dubbo-learn chuanzhou$ jstat -class 29159 1000 10
Loaded Bytes Unloaded Bytes Time
3204 6088.2 0 0.0 2.14 3204 6088.2 0 0.0 2.14 3204 6088.2 0 0.0 2.14 3204 6088.2 0 0.0 2.14 3204 6088.2 0 0.0 2.14 3204 6088.2 0 0.0 2.14 3204 6088.2 0 0.0 2.14 3204 6088.2 0 0.0 2.14 3204 6088.2 0 0.0 2.14 3204 6088.2 0 0.0 2.14 - Loaded：表示类加载的个数
- Bytes：表示类加载的大小，单位为kb
- UnLoaded：表示类卸载的个数
- Bytes：表示类卸载的大小，单位为kb
- Time：表示类加载和卸载的时间
3.2 垃圾收集
要查看一个java进程的垃圾收集器信息，可使用jstat -gc 进程id 每隔多少毫秒 一共输出多少次
MacBook-Pro:dubbo-learn chuanzhou$ jstat -gc 29159 1000 3
S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT GCT
5120.0 5120.0 4308.8 0.0 33280.0 17845.6 87552.0 88.0 18944.0 18304.7 2304.0 2144.9 2 0.014 0 0.000 0.014 5120.0 5120.0 4308.8 0.0 33280.0 17845.6 87552.0 88.0 18944.0 18304.7 2304.0 2144.9 2 0.014 0 0.000 0.014 5120.0 5120.0 4308.8 0.0 33280.0 17845.6 87552.0 88.0 18944.0 18304.7 2304.0 2144.9 2 0.014 0 0.000 0.014 S0C: Current survivor space 0 capacity (kB).表示survivor 0区的总大小S1C: Current survivor space 1 capacity (kB).表示survivor 1区的总大小S0U: Survivor space 0 utilization (kB).表示survivor 0区使用了的大小S1U: Survivor space 1 utilization (kB).表示survivor 1区使用了的大小EC: Current eden space capacity (kB).表示eden区总大小EU: Eden space utilization (kB).表示eden区使用了的大小OC: Current old space capacity (kB).表示old区总大小OU: Old space utilization (kB).表示old区使用了的大小MC: Metaspace capacity (kB).表示Metaspace区总大小MU: Metacspace utilization (kB).表示Metaspace区使用了的大小CCSC: Compressed class space capacity (kB).表示压缩类空间总量CCSU: Compressed class space used (kB).表示压缩类空间使用量YGC: Number of young generation garbage collection events.表示Young GC的次数YGCT: Young generation garbage collection time.表示Young GC的时间FGC: Number of full GC events.表示full GC的次数FGCT: Full garbage collection time.表示full GC的时间GCT: Total garbage collection time.表示总的 GC的时间
3.3 JIT编译
3.3.1 -compiler参数
MacBook-Pro:dubbo-learn chuanzhou$ jstat -compiler 29159 1000 5
Compiled Failed Invalid Time FailedType FailedMethod
1284 0 0 3.50 0 1284 0 0 3.50 0 1284 0 0 3.50 0 1284 0 0 3.50 0 1284 0 0 3.50 0 - Compiled：表示编译成功的方法数量
- Failed：表示编译失败的方法数量
- Invalid：表示编译无效的方法数量
- Time：编译所花费的时间
- FailedType：编译失败类型
- FailedMethod：编译失败方法
3.3.2 -printcompilation参数
4、jmap+MAT实战内存溢出
模拟内存溢出：
@RestController
public class MemoryController { private List<User> userList = new ArrayList<User>(); private List<Class<?>> classList = new ArrayList<Class<?>>(); /** * -Xmx32M -Xms32M * */ @GetMapping("/heap") public String heap() { int i=0; while(true) { userList.add(new User(i++, UUID.randomUUID().toString())); } } /** * -XX:MetaspaceSize=32M -XX:MaxMetaspaceSize=32M * */ @GetMapping("/nonheap") public String nonheap() { while(true) { classList.addAll(Metaspace.createClasses()); } } } package com.imooc.monitor_tuning.chapter2;
import java.util.ArrayList;
import java.util.List;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor; import org.objectweb.asm.Opcodes; /* * https://blog.youkuaiyun.com/bolg_hero/article/details/78189621 * 继承ClassLoader是为了方便调用defineClass方法，因为该方法的定义为protected * */ public class Metaspace extends ClassLoader { public static List<Class<?>> createClasses() { // 类持有 List<Class<?>> classes = new ArrayList<Class<?>>(); // 循环1000w次生成1000w个不同的类。 for (int i = 0; i < 10000000; ++i) { ClassWriter cw = new ClassWriter(0); // 定义一个类名称为Class{i}，它的访问域为public，父类为java.lang.Object，不实现任何接口 cw.visit(Opcodes.V1_1, Opcodes.ACC_PUBLIC, "Class" + i, null, "java/lang/Object", null); // 定义构造函数<init>方法 MethodVisitor mw = cw.visitMethod(Opcodes.ACC_PUBLIC, "<init>", "()V", null, null); // 第一个指令为加载this mw.visitVarInsn(Opcodes.ALOAD, 0); // 第二个指令为调用父类Object的构造函数 mw.visitMethodInsn(Opcodes.INVOKESPECIAL, "java/lang/Object", "<init>", "()V"); // 第三条指令为return mw.visitInsn(Opcodes.RETURN); mw.visitMaxs(1, 1); mw.visitEnd(); Metaspace test = new Metaspace(); byte[] code = cw.toByteArray(); // 定义类 Class<?> exampleClass = test.defineClass("Class" + i, code, 0, code.length); classes.add(exampleClass); } return classes; } } package com.imooc.monitor_tuning.chapter2;
public class User { private int id; private String name; public User(int id, String name) { super(); this.id = id; this.name = name; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } } 设置启动参数：
启动参数
启动application，发现出现内存溢出
4.1 如何导出内存溢出映像文件
4.2 内存溢出自动导出
-XX:+HeapDumpOnOutOfMemoryError-XX:HeapDumpPath=./
4.3 使用jmap命令手动导出
格式：jmap -dump:format=b,file=路径/heap.hprof 进程id
其他命令：jmap -heap 进程id 查看堆信息
[root@izwz93osmk5vi5qwqyscxaz bin]# ./jmap -heap 9723
Attaching to process ID 9723, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.72-b15
using thread-local object allocation.
Mark Sweep Compact GC
Heap Configuration:
MinHeapFreeRatio = 40 MaxHeapFreeRatio = 70 MaxHeapSize = 482344960 (460.0MB) NewSize = 10485760 (10.0MB) MaxNewSize = 160759808 (153.3125MB) OldSize = 20971520 (20.0MB) NewRatio = 2 SurvivorRatio = 8 MetaspaceSize = 21807104 (20.796875MB) CompressedClassSpaceSize = 1073741824 (1024.0MB) MaxMetaspaceSize = 17592186044415 MB G1HeapRegionSize = 0 (0.0MB) Heap Usage: New Generation (Eden + 1 Survivor Space): capacity = 32178176 (30.6875MB) used = 16081160 (15.336189270019531MB) free = 16097016 (15.351310729980469MB) 49.97536218336303% used Eden Space: capacity = 28639232 (27.3125MB) used = 16054760 (15.311012268066406MB) free = 12584472 (12.001487731933594MB) 56.058626153103546% used From Space: capacity = 3538944 (3.375MB) used = 26400 (0.025177001953125MB) free = 3512544 (3.349822998046875MB) 0.7459852430555556% used To Space: capacity = 3538944 (3.375MB) used = 0 (0.0MB) free = 3538944 (3.375MB) 0.0% used tenured generation: capacity = 71221248 (67.921875MB) used = 57115304 (54.469398498535156MB) free = 14105944 (13.452476501464844MB) 80.19419148622613% used 27532 interned Strings occupying 3194040 bytes. 4.4 使用MAT分析映像文件
MAT分析
- Class Name：类名
- Objects：对象数量
- Shallow Heap：
- Retained Heap：占用的内存大小
右键查看com.imooc.monitor_tuning.chapter2.User的强引用
image.png
image.png
也可以查看对象树：
对象树
5、jstack实战死循环与死锁
格式：jstack 进程id
2018-09-05 07:59:21
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.72-b15 mixed mode):
"Attach Listener" #16 daemon prio=9 os_prio=0 tid=0x00007f3d9c001000 nid=0x521f waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"localhost-startStop-1" #15 daemon prio=5 os_prio=0 tid=0x00007f3dac002800 nid=0x5208 runnable [0x00007f3da15d1000]
java.lang.Thread.State: RUNNABLE
at java.io.FileInputStream.readBytes(Native Method)
at java.io.FileInputStream.read(FileInputStream.java:255)
at sun.security.provider.SeedGenerator$URLSeedGenerator.getSeedBytes(SeedGenerator.java:539) at sun.security.provider.SeedGenerator.generateSeed(SeedGenerator.java:144) at sun.security.provider.SecureRandom$SeederHolder.<clinit>(SecureRandom.java:203) at sun.security.provider.SecureRandom.engineNextBytes(SecureRandom.java:221) - locked <0x00000000e3e90be0> (a sun.security.provider.SecureRandom) at java.security.SecureRandom.nextBytes(SecureRandom.java:468) - locked <0x00000000e3e910c0> (a java.security.SecureRandom) at java.security.SecureRandom.next(SecureRandom.java:491) at java.util.Random.nextInt(Random.java:329) at org.apache.catalina.util.SessionIdGeneratorBase.createSecureRandom(SessionIdGeneratorBase.java:240) at org.apache.catalina.util.SessionIdGeneratorBase.getRandomBytes(SessionIdGeneratorBase.java:174) at org.apache.catalina.util.StandardSessionIdGenerator.generateSessionId(StandardSessionIdGenerator.java:34) at org.apache.catalina.util.SessionIdGeneratorBase.generateSessionId(SessionIdGeneratorBase.java:167) at org.apache.catalina.util.SessionIdGeneratorBase.startInternal(SessionIdGeneratorBase.java:260) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145) - locked <0x00000000e3e90730> (a org.apache.catalina.util.StandardSessionIdGenerator) at org.apache.catalina.session.ManagerBase.startInternal(ManagerBase.java:717) at org.apache.catalina.session.StandardManager.startInternal(StandardManager.java:352) - locked <0x00000000e42eefb0> (a org.apache.catalina.session.StandardManager) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145) - locked <0x00000000e42eefb0> (a org.apache.catalina.session.StandardManager) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5339) - locked <0x00000000ed3c6ca0> (a org.apache.catalina.core.StandardContext) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145) - locked <0x00000000ed3c6ca0> (a org.apache.catalina.core.StandardContext) at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:753) at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:729) at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:717) at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:974) at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1850) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) "Catalina-startStop-1" #14 daemon prio=5 os_prio=0 tid=0x00007f3dc4437000 nid=0x5207 waiting on condition [0x00007f3da16d2000] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park(Native Method) - parking to wait for <0x00000000ed3c6fc0> (a java.util.concurrent.FutureTask) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175) at java.util.concurrent.FutureTask.awaitDone(FutureTask.java:429) at java.util.concurrent.FutureTask.get(FutureTask.java:191) at org.apache.catalina.startup.HostConfig.deployWARs(HostConfig.java:766) at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:436) at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1580) at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:322) at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:95) at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90) at org.apache.catalina.util.LifecycleBase.setStateInternal(LifecycleBase.java:388) - locked <0x00000000ed03ec38> (a org.apache.catalina.core.StandardHost) at org.apache.catalina.util.LifecycleBase.setState(LifecycleBase.java:333) - locked <0x00000000ed03ec38> (a org.apache.catalina.core.StandardHost) at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:960) - locked <0x00000000ed03ec38> (a org.apache.catalina.core.StandardHost) at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:871) - locked <0x00000000ed03ec38> (a org.apache.catalina.core.StandardHost) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145) - locked <0x00000000ed03ec38> (a org.apache.catalina.core.StandardHost) at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1408) at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1398) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) "NioBlockingSelector.BlockPoller-2" #13 daemon prio=5 os_prio=0 tid=0x00007f3dc4429800 nid=0x5206 runnable [0x00007f3da17d4000] java.lang.Thread.State: RUNNABLE at sun.nio.ch.EPollArrayWrapper.epollWait(Native Method) at sun.nio.ch.EPollArrayWrapper.poll(EPollArrayWrapper.java:269) at sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:93) at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86) - locked <0x00000000ed3c75a8> (a sun.nio.ch.Util$2) - locked <0x00000000ed3c75b8> (a java.util.Collections$UnmodifiableSet) - locked <0x00000000ed3c7560> (a sun.nio.ch.EPollSelectorImpl) at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97) at org.apache.tomcat.util.net.NioBlockingSelector$BlockPoller.run(NioBlockingSelector.java:301) "NioBlockingSelector.BlockPoller-1" #12 daemon prio=5 os_prio=0 tid=0x00007f3dc440e800 nid=0x5205 runnable [0x00007f3da18d5000] java.lang.Thread.State: RUNNABLE at sun.nio.ch.EPollArrayWrapper.epollWait(Native Method) at sun.nio.ch.EPollArrayWrapper.poll(EPollArrayWrapper.java:269) at sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:93) at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86) - locked <0x00000000ed3c77e0> (a sun.nio.ch.Util$2) - locked <0x00000000ed3c77f0> (a java.util.Collections$UnmodifiableSet) - locked <0x00000000ed3c7798> (a sun.nio.ch.EPollSelectorImpl) at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97) at org.apache.tomcat.util.net.NioBlockingSelector$BlockPoller.run(NioBlockingSelector.java:301) "GC Daemon" #11 daemon prio=2 os_prio=0 tid=0x00007f3dc4356800 nid=0x5204 in Object.wait() [0x00007f3dc81a0000] java.lang.Thread.State: TIMED_WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000000ed0d57f0> (a sun.misc.GC$LatencyLock) at sun.misc.GC$Daemon.run(GC.java:117) - locked <0x00000000ed0d57f0> (a sun.misc.GC$LatencyLock) "AsyncFileHandlerWriter-789451787" #10 daemon prio=5 os_prio=0 tid=0x00007f3dc4105000 nid=0x5203 waiting on condition [0x00007f3dc8338000] java.lang.Thread.State: TIMED_WAITING (parking) at sun.misc.Unsafe.park(Native Method) - parking to wait for <0x00000000ecec1210> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject) at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215) at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078) at java.util.concurrent.LinkedBlockingDeque.pollFirst(LinkedBlockingDeque.java:522) at java.util.concurrent.LinkedBlockingDeque.poll(LinkedBlockingDeque.java:684) at org.apache.juli.AsyncFileHandler$LoggerThread.run(AsyncFileHandler.java:153) "Service Thread" #7 daemon prio=9 os_prio=0 tid=0x00007f3dc40b3800 nid=0x5201 runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE "C1 CompilerThread1" #6 daemon prio=9 os_prio=0 tid=0x00007f3dc40b0800 nid=0x5200 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "C2 CompilerThread0" #5 daemon prio=9 os_prio=0 tid=0x00007f3dc40ae800 nid=0x51ff waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "Signal Dispatcher" #4 daemon prio=9 os_prio=0 tid=0x00007f3dc40ad000 nid=0x51fe runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE "Finalizer" #3 daemon prio=8 os_prio=0 tid=0x00007f3dc407a000 nid=0x51fd in Object.wait() [0x00007f3dc893e000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000000ecec2320> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143) - locked <0x00000000ecec2320> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:164) at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209) "Reference Handler" #2 daemon prio=10 os_prio=0 tid=0x00007f3dc4075000 nid=0x51fc in Object.wait() [0x00007f3dc8a3f000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000000ecec24d8> (a java.lang.ref.Reference$Lock) at java.lang.Object.wait(Object.java:502) at java.lang.ref.Reference.tryHandlePending(Reference.java:191) - locked <0x00000000ecec24d8> (a java.lang.ref.Reference$Lock) at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153) "main" #1 prio=5 os_prio=0 tid=0x00007f3dc4009000 nid=0x51fa waiting on condition [0x00007f3dcc417000] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park(Native Method) - parking to wait for <0x00000000ed3c7340> (a java.util.concurrent.FutureTask) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175) at java.util.concurrent.FutureTask.awaitDone(FutureTask.java:429) at java.util.concurrent.FutureTask.get(FutureTask.java:191) at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:943) - locked <0x00000000ecfb7038> (a org.apache.catalina.core.StandardEngine) at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:262) - locked <0x00000000ecfb7038> (a org.apache.catalina.core.StandardEngine) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145) - locked <0x00000000ecfb7038> (a org.apache.catalina.core.StandardEngine) at org.apache.catalina.core.StandardService.startInternal(StandardService.java:441) - locked <0x00000000ecfb7038> (a org.apache.catalina.core.StandardEngine) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145) - locked <0x00000000ecfa2330> (a org.apache.catalina.core.StandardService) at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:789) - locked <0x00000000ecf4e258> (a java.lang.Object) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145) - locked <0x00000000ecf1c578> (a org.apache.catalina.core.StandardServer) at org.apache.catalina.startup.Catalina.start(Catalina.java:641) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:349) at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:483) "VM Thread" os_prio=0 tid=0x00007f3dc406d800 nid=0x51fb runnable "VM Periodic Task Thread" os_prio=0 tid=0x00007f3dc40b7000 nid=0x5202 waiting on condition JNI global references: 59 - localhost-startStop-1：线程名
- daemon：后台线程
- prio：优先级
- os_prio：系统优先级
- tid：线程id
- nid：操作系统id
- java.lang.Thread.State：线程状态；NEW-线程尚未启动， RUNNABLE- 线程运行中，BLOCKED-等待一个锁， WAITINH-等待另一个线程， TIMED_WAITING-限时等待另一个线程， TERMINATED-已退出
5.1 实战死循环
import java.util.ArrayList;
import java.util.List;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController public class CpuController { /** * 死循环 * */ @RequestMapping("/loop") public List<Long> loop(){ String data = "{\"data\":[{\"partnerid\":]"; return getPartneridsFromJson(data); } private Object lock1 = new Object(); private Object lock2 = new Object(); /** * 死锁 * */ @RequestMapping("/deadlock") public String deadlock(){ new Thread(()->{ synchronized(lock1) { try {Thread.sleep(1000);}catch(Exception e) {} synchronized(lock2) { System.out.println("Thread1 over"); } } }) .start(); new Thread(()->{ synchronized(lock2) { try {Thread.sleep(1000);}catch(Exception e) {} synchronized(lock1) { System.out.println("Thread2 over"); } } }) .start(); return "deadlock"; } public static List<Long> getPartneridsFromJson(String data){ //{\"data\":[{\"partnerid\":982,\"count\":\"10000\",\"cityid\":\"11\"},{\"partnerid\":983,\"count\":\"10000\",\"cityid\":\"11\"},{\"partnerid\":984,\"count\":\"10000\",\"cityid\":\"11\"}]} //上面是正常的数据 List<Long> list = new ArrayList<Long>(2); if(data == null || data.length() <= 0){ return list; } int datapos = data.indexOf("data"); if(datapos < 0){ return list; } int leftBracket = data.indexOf("[",datapos); int rightBracket= data.indexOf("]",datapos); if(leftBracket < 0 || rightBracket < 0){ return list; } String partners = data.substring(leftBracket+1,rightBracket); if(partners == null || partners.length() <= 0){ return list; } while(partners!=null && partners.length() > 0){ int idpos = partners.indexOf("partnerid"); if(idpos < 0){ break; } int colonpos = partners.indexOf(":",idpos); int commapos = partners.indexOf(",",idpos); if(colonpos < 0 || commapos < 0){ //partners = partners.substring(idpos+"partnerid".length());//1 continue; } String pid = partners.substring(colonpos+1,commapos); if(pid == null || pid.length() <= 0){ //partners = partners.substring(idpos+"partnerid".length());//2 continue; } try{ list.add(Long.parseLong(pid)); }catch(Exception e){ //do nothing } partners = partners.substring(commapos); } return list; } } 访问/loop端点三次，然后使用top命令：
#导出线程堆栈
$ jstack 7930 > 7930.txt
#打印该进程下的线程
$ top -p 7930 -H 
#将十进制线程id转换为16进制
$ printf "%x" 8247
2037
然后在导出的7930.txt文件中找到2037
死循环
访问/loop端点，制造死循环，使用jstack命令导出线程堆栈信息：
死锁
最后一行已提示：Found 1 deadlock
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