本文主要是介绍JVM在线分析-解决问题的工具一(jinfo,jmap,jstack)，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
1. jinfo
(base) PS C:\Users\zishi\Desktop> jinfo
Usage:jinfo <option> <pid>(to connect to a running process)where <option> is one of:-flag <name> to print the value of the named VM flag #输出对应名称的参数-flag [+|-]<name> to enable or disable the named VM flag# 开启或者关闭对应名称的参数 只有被标记为 manageable 的参数才可以被动态修改-flag <name>=<value> to set the named VM flag to the given value #设定对应名称的参数-flags to print VM flags # 输出全部的参数-sysprops to print Java system properties #输出系统属性<no option> to print both VM flags and system properties -? | -h | --help | -help to print this help message
(base) PS C:\Users\zishi> jinfo 9368
Java System Properties:
#Thu Nov 09 09:05:06 CST 2023
sun.desktop=windows
awt.toolkit=sun.awt.windows.WToolkit
java.specification.version=11
sun.cpu.isalist=amd64
sun.jnu.encoding=GBK
java.class.path=.\\quality-server.jar
java.vm.vendor=Oracle Corporation
sun.arch.data.model=64
user.variant=
catalina.useNaming=false
java.vendor.url=https\://openjdk.java.net/
。。。。略去
(base) PS C:\Users\zishi> jinfo -sysprops 9368
Java System Properties:
#Thu Nov 09 09:07:07 CST 2023
sun.desktop=windows
awt.toolkit=sun.awt.windows.WToolkit
。。。。略去
(base) PS C:\Users\zishi> jinfo -flags 9368
VM Flags:
-XX:CICompilerCount=4
-XX:ConcGCThreads=3
-XX:G1ConcRefinementThreads=10
-XX:G1HeapRegionSize=2097152
-XX:GCDrainStackTargetSize=64
-XX:InitialHeapSize=534773760
-XX:MarkStackSize=4194304
-XX:MaxHeapSize=8524922880
-XX:MaxNewSize=5114953728
-XX:MinHeapDeltaBytes=2097152
-XX:NonNMethodCodeHeapSize=5836300
-XX:NonProfiledCodeHeapSize=122910970
-XX:ProfiledCodeHeapSize=122910970
-XX:ReservedCodeCacheSize=251658240
-XX:+SegmentedCodeCache
-XX:+UseCompressedClassPointers
-XX:+UseCompressedOops
-XX:+UseG1GC
-XX:-UseLargePagesIndividualAllocation
(base) PS C:\Users\zishi> jinfo -flag MaxHeapSize 9368
-XX:MaxHeapSize=8524922880
(base) PS C:\Users\zishi> jinfo -flag MaxHeapSize=8524922883 9368
Exception in thread "main" com.sun.tools.attach.AttachOperationFailedException: flag 'MaxHeapSize' cannot be changedat jdk.attach/sun.tools.attach.VirtualMachineImpl.execute(VirtualMachineImpl.java:130)at jdk.attach/sun.tools.attach.HotSpotVirtualMachine.executeCommand(HotSpotVirtualMachine.java:309)at jdk.attach/sun.tools.attach.HotSpotVirtualMachine.setFlag(HotSpotVirtualMachine.java:282)at jdk.jcmd/sun.tools.jinfo.JInfo.flag(JInfo.java:146)at jdk.jcmd/sun.tools.jinfo.JInfo.main(JInfo.java:127)
查看被标记为 manageable 的参数
$ java -XX:+PrintFlagsFinal -version | grep manageableintx CMSAbortablePrecleanWaitMillis = 100 {manageable} {default}intx CMSTriggerInterval = -1 {manageable} {default}intx CMSWaitDuration = 2000 {manageable} {default}bool HeapDumpAfterFullGC = false {manageable} {default}bool HeapDumpBeforeFullGC = false {manageable} {default}bool HeapDumpOnOutOfMemoryError = false {manageable} {default}ccstr HeapDumpPath = {manageable} {default}uintx MaxHeapFreeRatio = 70 {manageable} {default}uintx MinHeapFreeRatio = 40 {manageable} {default}bool PrintClassHistogram = false {manageable} {default}bool PrintConcurrentLocks = false {manageable} {default}
java version "11.0.13" 2021-10-19 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.13+10-LTS-370)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.13+10-LTS-370, mixed mode)
修改参数的值
(base) PS C:\Users\zishi> jinfo -flag MaxHeapFreeRatio 9368
-XX:MaxHeapFreeRatio=70
(base) PS C:\Users\zishi> jinfo -flag MaxHeapFreeRatio=80 9368
(base) PS C:\Users\zishi> jinfo -flag MaxHeapFreeRatio 9368
-XX:MaxHeapFreeRatio=80
开启参数：
(base) PS C:\Users\zishi> jinfo -flag HeapDumpBeforeFullGC 9368
-XX:-HeapDumpBeforeFullGC
(base) PS C:\Users\zishi> jinfo -flag +HeapDumpBeforeFullGC 9368
(base) PS C:\Users\zishi> jinfo -flag HeapDumpBeforeFullGC 9368
-XX:+HeapDumpBeforeFullGC
扩展
java -XX:+PrintFlagsInitial 查看所有 JVM 参数启动的初始值
java -XX:+PrintFlagsFinal 查看所有 JVM 参数的最终值
java -XX:+PrintCommandLineFlags 查看哪些已经被用户或者 JVM 设置过的详细的 XX 参数的名称和值
2. jmap
(base) PS C:\Users\zishi> jmap
Usage:jmap -clstats <pid>to connect to running process and print class loader statisticsjmap -finalizerinfo <pid>to connect to running process and print information on objects awaiting finalizationjmap -histo[:live] <pid>to connect to running process and print histogram of java object heapif the "live" suboption is specified, only count live objectsjmap -dump:<dump-options> <pid>to connect to running process and dump java heapjmap -? -h --helpto print this help messagedump-options:live dump only live objects; if not specified,all objects in the heap are dumped.format=b binary formatfile=<file> dump heap to <file>Example: jmap -dump:live,format=b,file=heap.bin <pid>
$ jmap -clstats 9368 > a.txt
$ cat a.txt | head -n 10
Index Super InstBytes KlassBytes annotations CpAll MethodCount Bytecodes MethodAll ROAll RWAll Total ClassName1 -1 10510264 504 0 0 0 0 0 24 616 640 [B2 8286 5545320 1112 0 6816 47 1117 27912 6480 30104 36584 java.lang.reflect.Method3 18 4025232 616 128 14264 109 4576 71992 18640 69664 88304 java.lang.String4 18 2461504 592 0 1360 9 213 2720 1488 3520 5008 java.util.concurrent.ConcurrentHashMap$Node5 -1 2286832 504 0 0 0 0 0 24 616 640 [Ljava.lang.Object;6 -1 2075104 504 0 0 0 0 0 32 616 648 [Ljava.util.HashMap$Node;7 18 2013216 584 0 1384 7 149 1816 1152 2952 4104 java.util.HashMap$Node8 7 1977960 584 0 504 1 10 624 304 1640 1944 java.util.LinkedHashMap$Entry9 18 1720280 672 0 22112 139 5679 85040 24632 85104 109736 java.lang.Class$ jmap -clstats 9368 | grep com.zishi.docuvate.exception4077 18 16 552 56 2568 6 282 1576 1448 3504 4952 com.zishi.docuvate.exception.GlobalExceptionHandler7429 7856 0 624 0 440 3 54 568 464 1368 1832 com.zishi.docuvate.exception.BadRequestException7430 7856 0 640 0 624 8 105 1472 1072 1952 3024 com.zishi.docuvate.exception.GlobalException说明：
Index
Super
InstBytes
KlassBytes
annotations
CpAll
MethodCount
Bytecodes
MethodAll
ROAll
RWAll
Total
ClassName： 类的完全限定名
(base) PS C:\Users\zishi> jmap -histo 23152num #instances #bytes class name (module)
-------------------------------------------------------1: 1164144 152211432 [B (java.base@11.0.13)2: 147373 44824568 [I (java.base@11.0.13)3: 694738 16673712 java.lang.String (java.base@11.0.13)4: 601819 12621496 [Ljava.lang.Class; (java.base@11.0.13)5: 107422 9453136 java.lang.reflect.Method (java.base@11.0.13)6: 113936 7291904 java.net.URL (java.base@11.0.13)7: 141772 4536704 org.springframework.boot.loader.jar.StringSequence8: 75593 4434728 [Ljava.lang.Object; (java.base@11.0.13)9: 178622 4286928 java.lang.StringBuilder (java.base@11.0.13)10: 102026 4081040 org.springframework.core.annotation.TypeMappedAnnotations11: 36093 2871384 [Ljava.util.HashMap$Node; (java.base@11.0.13)12: 88017 2816544 java.util.concurrent.ConcurrentHashMap$Node (java.base@11.0.13)13: 84459 2702688 org.springframework.core.annotation.TypeMappedAnnotations$MergedAnnotationFinder14: 82805 2649760 java.util.HashMap$Node (java.base@11.0.13)15: 64740 2589600 java.util.LinkedHashMap$Entry (java.base@11.0.13)16: 49166 2359968 java.util.HashMap (java.base@11.0.13)17: 92807 2227368 org.springframework.boot.loader.jar.JarURLConnection$JarEntryName18: 12370 2153808 [C (java.base@11.0.13)
说明：
#instances：对象数量
#bytes： 占用内存大小(单位：字节)
class name (module)： 类的完全限定名
3. jstack
(base) PS C:\Users\zishi> jstack
Usage:jstack [-l][-e] <pid>(to connect to running process)Options:-l long listing. Prints additional information about locks-e extended listing. Prints additional information about threads-? -h --help -help to print this help message
代码示例：
/*** 当DeadLock类的对象flag==1时（td1），先锁定o1,睡眠500毫秒* 而td1在睡眠的时候另一个flag==0的对象（td2）线程启动，先锁定o2,睡眠500毫秒* td1睡眠结束后需要锁定o2才能继续执行，而此时o2已被td2锁定；* td2睡眠结束后需要锁定o1才能继续执行，而此时o1已被td1锁定；* td1、td2相互等待，都需要得到对方锁定的资源才能继续执行，从而死锁。*/
public class DeadLockTest implements Runnable{public int flag = 1;//静态对象是类的所有对象共享的private static Object o1 = new Object(), o2 = new Object();@Overridepublic void run() {System.out.println("flag=" + flag);if (flag == 1) {synchronized (o1) {try {Thread.sleep(500);} catch (Exception e) {e.printStackTrace();}synchronized (o2) {System.out.println("1");}}}if (flag == 0) {synchronized (o2) {try {Thread.sleep(500);} catch (Exception e) {e.printStackTrace();}synchronized (o1) {System.out.println("0");}}}}public static void main(String[] args) {DeadLockTest td1 = new DeadLockTest();DeadLockTest td2 = new DeadLockTest();td1.flag = 1;td2.flag = 0;//td1,td2都处于可执行状态，但JVM线程调度先执行哪个线程是不确定的。//td2的run()可能在td1的run()之前运行new Thread(td1).start();new Thread(td2).start();}
}编译运行，执行jstack
(base) PS C:\Users\zishi> jstack 21744
2023-11-09 18:47:14
Full thread dump Java HotSpot(TM) 64-Bit Server VM (11.0.13+10-LTS-370 mixed mode):Threads class SMR info:
_java_thread_list=0x000001d91fca51a0, length=12, elements={
0x000001d91fa90800, 0x000001d91fab5800, 0x000001d91fb2b800, 0x000001d91fb2c800,
0x000001d91fb2e000, 0x000001d91fb31000, 0x000001d91fb32800, 0x000001d91fb35800,
0x000001d91fcb6800, 0x000001d91fcbc000, 0x000001d91fcbc800, 0x000001d972982000
}"Reference Handler" #2 daemon prio=10 os_prio=2 cpu=0.00ms elapsed=18.72s tid=0x000001d91fa90800 nid=0x2aac waiting on condition [0x000000aacf8ff000]java.lang.Thread.State: RUNNABLEat java.lang.ref.Reference.waitForReferencePendingList(java.base@11.0.13/Native Method)at java.lang.ref.Reference.processPendingReferences(java.base@11.0.13/Reference.java:241)at java.lang.ref.Reference$ReferenceHandler.run(java.base@11.0.13/Reference.java:213)"Finalizer" #3 daemon prio=8 os_prio=1 cpu=0.00ms elapsed=18.72s tid=0x000001d91fab5800 nid=0x2224 in Object.wait() [0x000000aacf9fe000]java.lang.Thread.State: WAITING (on object monitor)at java.lang.Object.wait(java.base@11.0.13/Native Method)- waiting on <0x0000000623a08fa8> (a java.lang.ref.ReferenceQueue$Lock)at java.lang.ref.ReferenceQueue.remove(java.base@11.0.13/ReferenceQueue.java:155)- waiting to re-lock in wait() <0x0000000623a08fa8> (a java.lang.ref.ReferenceQueue$Lock)at java.lang.ref.ReferenceQueue.remove(java.base@11.0.13/ReferenceQueue.java:176)at java.lang.ref.Finalizer$FinalizerThread.run(java.base@11.0.13/Finalizer.java:170)"Signal Dispatcher" #4 daemon prio=9 os_prio=2 cpu=0.00ms elapsed=18.70s tid=0x000001d91fb2b800 nid=0x3bcc runnable [0x0000000000000000]java.lang.Thread.State: RUNNABLE"Attach Listener" #5 daemon prio=5 os_prio=2 cpu=0.00ms elapsed=18.70s tid=0x000001d91fb2c800 nid=0x3740 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLE"Service Thread" #6 daemon prio=9 os_prio=0 cpu=0.00ms elapsed=18.70s tid=0x000001d91fb2e000 nid=0xd0c runnable [0x0000000000000000]java.lang.Thread.State: RUNNABLE"C2 CompilerThread0" #7 daemon prio=9 os_prio=2 cpu=0.00ms elapsed=18.70s tid=0x000001d91fb31000 nid=0x1620 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLENo compile task"C1 CompilerThread0" #10 daemon prio=9 os_prio=2 cpu=0.00ms elapsed=18.70s tid=0x000001d91fb32800 nid=0x133c waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLENo compile task"Sweeper thread" #11 daemon prio=9 os_prio=2 cpu=0.00ms elapsed=18.70s tid=0x000001d91fb35800 nid=0x1368 runnable [0x0000000000000000]java.lang.Thread.State: RUNNABLE"Common-Cleaner" #12 daemon prio=8 os_prio=1 cpu=0.00ms elapsed=18.67s tid=0x000001d91fcb6800 nid=0x1df8 in Object.wait() [0x000000aad01fe000]java.lang.Thread.State: TIMED_WAITING (on object monitor)at java.lang.Object.wait(java.base@11.0.13/Native Method)- waiting on <0x0000000623bf37f8> (a java.lang.ref.ReferenceQueue$Lock)at java.lang.ref.ReferenceQueue.remove(java.base@11.0.13/ReferenceQueue.java:155)- waiting to re-lock in wait() <0x0000000623bf37f8> (a java.lang.ref.ReferenceQueue$Lock)at jdk.internal.ref.CleanerImpl.run(java.base@11.0.13/CleanerImpl.java:148)at java.lang.Thread.run(java.base@11.0.13/Thread.java:834)at jdk.internal.misc.InnocuousThread.run(java.base@11.0.13/InnocuousThread.java:134)"Thread-0" #13 prio=5 os_prio=0 cpu=0.00ms elapsed=18.67s tid=0x000001d91fcbc000 nid=0x39d4 waiting for monitor entry [0x000000aad02ff000]java.lang.Thread.State: BLOCKED (on object monitor)at DeadLockTest.run(DeadLockTest.java:25)- waiting to lock <0x0000000623bf7078> (a java.lang.Object)- locked <0x0000000623bf7068> (a java.lang.Object)at java.lang.Thread.run(java.base@11.0.13/Thread.java:834)"Thread-1" #14 prio=5 os_prio=0 cpu=0.00ms elapsed=18.67s tid=0x000001d91fcbc800 nid=0x7f8 waiting for monitor entry [0x000000aad03ff000]java.lang.Thread.State: BLOCKED (on object monitor)at DeadLockTest.run(DeadLockTest.java:37)- waiting to lock <0x0000000623bf7068> (a java.lang.Object)- locked <0x0000000623bf7078> (a java.lang.Object)at java.lang.Thread.run(java.base@11.0.13/Thread.java:834)"DestroyJavaVM" #15 prio=5 os_prio=0 cpu=15.63ms elapsed=18.67s tid=0x000001d972982000 nid=0x5744 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLE"VM Thread" os_prio=2 cpu=0.00ms elapsed=18.73s tid=0x000001d91fa8f800 nid=0x222c runnable"GC Thread#0" os_prio=2 cpu=0.00ms elapsed=18.77s tid=0x000001d972996800 nid=0x5144 runnable"G1 Main Marker" os_prio=2 cpu=0.00ms elapsed=18.77s tid=0x000001d972a17800 nid=0x4180 runnable"G1 Conc#0" os_prio=2 cpu=0.00ms elapsed=18.77s tid=0x000001d972a19000 nid=0x3380 runnable"G1 Refine#0" os_prio=2 cpu=0.00ms elapsed=18.75s tid=0x000001d97fde5800 nid=0x2ba4 runnable"G1 Young RemSet Sampling" os_prio=2 cpu=0.00ms elapsed=18.75s tid=0x000001d97fde6800 nid=0x2f8c runnable
"VM Periodic Task Thread" os_prio=2 cpu=0.00ms elapsed=18.67s tid=0x000001d91fcb6000 nid=0x2990 waiting on conditionJNI global refs: 6, weak refs: 0Found one Java-level deadlock:
=============================
"Thread-0":waiting to lock monitor 0x000001d91fabff80 (object 0x0000000623bf7078, a java.lang.Object),which is held by "Thread-1"
"Thread-1":waiting to lock monitor 0x000001d91fabcc80 (object 0x0000000623bf7068, a java.lang.Object),which is held by "Thread-0"Java stack information for the threads listed above:
===================================================
"Thread-0":at DeadLockTest.run(DeadLockTest.java:25)- waiting to lock <0x0000000623bf7078> (a java.lang.Object)- locked <0x0000000623bf7068> (a java.lang.Object)at java.lang.Thread.run(java.base@11.0.13/Thread.java:834)
"Thread-1":at DeadLockTest.run(DeadLockTest.java:37)- waiting to lock <0x0000000623bf7068> (a java.lang.Object)- locked <0x0000000623bf7078> (a java.lang.Object)at java.lang.Thread.run(java.base@11.0.13/Thread.java:834)Found 1 deadlock.
说明：
Thread-1：线程名
prio：优先级
os_prio：操作系统级别的线程优先级
tid：线程id
nid：线程对应本地线程id
java.lang.Thread.State：线程状态
可以看到有一个 dead lock
Found one Java-level deadlock:
jstack还帮我们打印了死锁产生的原因
打印了死锁产生的原因之外，还帮我们定位到了java的代码行数：
Found one Java-level deadlock:
=============================
"Thread-0":waiting to lock monitor 0x000001d91fabff80 (object 0x0000000623bf7078, a java.lang.Object),which is held by "Thread-1"
"Thread-1":waiting to lock monitor 0x000001d91fabcc80 (object 0x0000000623bf7068, a java.lang.Object),which is held by "Thread-0"Java stack information for the threads listed above:
===================================================
"Thread-0":at DeadLockTest.run(DeadLockTest.java:25)- waiting to lock <0x0000000623bf7078> (a java.lang.Object)- locked <0x0000000623bf7068> (a java.lang.Object)at java.lang.Thread.run(java.base@11.0.13/Thread.java:834)
"Thread-1":at DeadLockTest.run(DeadLockTest.java:37)- waiting to lock <0x0000000623bf7068> (a java.lang.Object)- locked <0x0000000623bf7078> (a java.lang.Object)at java.lang.Thread.run(java.base@11.0.13/Thread.java:834)Found 1 deadlock.
参考：
https://juejin.cn/post/6957903936657293319#heading-3
这篇关于JVM在线分析-解决问题的工具一(jinfo,jmap,jstack)的文章就介绍到这儿，希望我们推荐的文章对编程师们有所帮助！
