内容大纲： 涵盖java以下常用工具的概念和用法，及其常用案例 jps，jstat，jinfo，jmap，jhat，jstack 使用频率最高的JDK命令工具：可以列出正在运行的JVM进程，并可以显示出JVM执行主类和进程号（LVMID:本地虚拟机唯一ID） 此处较为简单，不做详解，可自行实验 功能：实时查看和调整JVM各项参数 jps -v可以查看显式指定的参数，但要知道未被指定的参数默认值，需要用jinfo 首先指定java程序，并设置参数 某些机器不支持动态修改 某些机器不支持动态修改 监视进程运行中的jvm物理内存的占用情况 dump文件可以用MAT等分析，关于如何分析，此处挖个坑，后续填补 dump文件分析工具，可用刚刚dump的文件 开启后，可通过https://127.0.0.1:7000/访问 观察jvm中当前所有线程的运行情况和线程当前状态。程序崩溃或卡住是贼好用 写了一个死锁的程序作为调试程序 用于监控JVM各种运行状态信息，运行期间定位JVM性能问题的首选 命令格式： 当监控时间不传入时，只记录当前一次的情况
文章目录
jps
1.常用命令
命令
作用
jps
显示进程号和主类名
jps -l
显示进程号和主类全名
jps -m
输出执行主类main()函数的参数
jps -v
输出启动时JVM参数
2.实战
jinfo
1.常用命令参数
命令
作用
-flag name
输出指定的参数
-flag [+|-] name
开-关指定参数
-flag name=value
输出执行主类main()函数的参数
-flags
输出给JVM默认和命令行传递的参数
-sysprops
输出Java系统配置
2.实战
java -Xms10M -Xmx100M jvm.DeadLock 输出指定参数
> jinfo -flag MaxHeapSize 13301 -XX:MaxHeapSize=4294967296 > jinfo -flag InitialHeapSize 13301 -XX:InitialHeapSize=268435456 输出所有默认参数和设置的参数
> jinfo -flags 13757 Attaching to process ID 13757, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.151-b12 Non-default VM flags: -XX:CICompilerCount=4 -XX:InitialHeapSize=10485760 -XX:MaxHeapSize=104857600 -XX:MaxNewSize=34603008 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=3145728 -XX:OldSize=7340032 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps -XX:+UseParallelGC Command line: -Xms10M -Xmx100M 开启关闭指定参数
> jinfo -flag -MaxHeapSize 13757 > jinfo -flag +MaxHeapSize 13757 动态修改指定参数
> jinfo -flag MaxHeapSize=20971520 13757 jmap
1. 常用命令参数
命令
作用
-dump:[live,]format=b,file=
输出jvm的heap内容到文件,live可选，代表只输出活的对象到文件
-finalizerinfo
打印正等候回收的对象的信息
-heap
打印heap的概要信息，GC算法，heap的配置及内存
-histo
打印每个class的实例数目,内存占用,类全名信息
-sysprops
输出Java系统配置
2. 实战
转存dump文件。
jmap -dump:format=b,file=Downloads/dump.bin 13757 Dumping heap to /Users/xiaoran/Downloads/dump.bin ... Heap dump file created 打印等待回收对象
> jmap -finalizerinfo 13757 Attaching to process ID 13757, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.151-b12 Number of objects pending for finalization: 0 (等待回收对象0个) 打印heap重要信息
> jmap -heap 13757 Attaching to process ID 13757, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.151-b12 using thread-local object allocation. Parallel GC with 8 thread(s) Heap Configuration: MinHeapFreeRatio = 0 MaxHeapFreeRatio = 100 MaxHeapSize = 104857600 (100.0MB) NewSize = 3145728 (3.0MB) MaxNewSize = 34603008 (33.0MB) OldSize = 7340032 (7.0MB) NewRatio = 2 SurvivorRatio = 8 MetaspaceSize = 21807104 (20.796875MB) CompressedClassSpaceSize = 1073741824 (1024.0MB) MaxMetaspaceSize = 17592186044415 MB G1HeapRegionSize = 0 (0.0MB) Heap Usage: PS Young Generation Eden Space: capacity = 2097152 (2.0MB) used = 0 (0.0MB) free = 2097152 (2.0MB) 0.0% used From Space: capacity = 524288 (0.5MB) used = 0 (0.0MB) free = 524288 (0.5MB) 0.0% used To Space: capacity = 524288 (0.5MB) used = 0 (0.0MB) free = 524288 (0.5MB) 0.0% used PS Old Generation capacity = 7340032 (7.0MB) used = 450216 (0.42935943603515625MB) free = 6889816 (6.570640563964844MB) 6.133706229073661% used 929 interned Strings occupying 65848 bytes. 打印class信息
> jmap -histo 13757 num #instances #bytes class name ---------------------------------------------- 1: 1421 124632 [C 2: 701 80000 java.lang.Class 3: 810 36832 [Ljava.lang.Object; 4: 1408 33792 java.lang.String 5: 15 25912 [B 6: 185 10360 java.lang.invoke.MemberName 7: 273 8736 java.util.concurrent.ConcurrentHashMap$Node jhat
jhat /Users/xiaoran/Downloads/dump.bin jstack
1. 常用命令参数
命令
作用
-F
正常请求不被响应，强制输出线程堆栈
-l
除堆栈外，锁的信息
-m
如调用本地方法，可显示c/c++堆栈
2. 实战
强制输出线程堆栈
> jstack -F 13757 Attaching to process ID 13757, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.151-b12 Deadlock Detection: Found one Java-level deadlock: ============================= "Thread-0": waiting to lock Monitor@0x00007f863f02aea8 (Object@0x00000007b9c08c00, a java/lang/Boolean), which is held by "Thread-1" "Thread-1": waiting to lock Monitor@0x00007f863f0286c8 (Object@0x00000007b9c08580, a java/lang/Boolean), which is held by "Thread-0" Found a total of 1 deadlock. Thread 18955: (state = BLOCKED) Thread 3843: (state = BLOCKED) Thread 43011: (state = BLOCKED) - jvm.DeadLock$2.run() @bci=63, line=57 (Interpreted frame) - java.lang.Thread.run() @bci=11, line=748 (Interpreted frame) Thread 21763: (state = BLOCKED) - jvm.DeadLock$1.run() @bci=63, line=36 (Interpreted frame) - java.lang.Thread.run() @bci=11, line=748 (Interpreted frame) Thread 18435: (state = BLOCKED) Thread 19715: (state = BLOCKED) - java.lang.Object.wait(long) @bci=0 (Interpreted frame) - java.lang.ref.ReferenceQueue.remove(long) @bci=59, line=143 (Interpreted frame) - java.lang.ref.ReferenceQueue.remove() @bci=2, line=164 (Interpreted frame) - java.lang.ref.Finalizer$FinalizerThread.run() @bci=36, line=209 (Interpreted frame) Thread 19971: (state = BLOCKED) - java.lang.Object.wait(long) @bci=0 (Interpreted frame) - java.lang.Object.wait() @bci=2, line=502 (Interpreted frame) - java.lang.ref.Reference.tryHandlePending(boolean) @bci=54, line=191 (Interpreted frame) - java.lang.ref.Reference$ReferenceHandler.run() @bci=1, line=153 (Interpreted frame) 输出堆栈信息和锁的信息
> jstack -l 13757 //此处省略若干，关注锁的信息 Found one Java-level deadlock: ============================= "Thread-1": waiting to lock monitor 0x00007f863f0286c8 (object 0x00000007b9c08580, a java.lang.Boolean), which is held by "Thread-0" "Thread-0": waiting to lock monitor 0x00007f863f02aea8 (object 0x00000007b9c08c00, a java.lang.Boolean), which is held by "Thread-1" Java stack information for the threads listed above: =================================================== "Thread-1": at jvm.DeadLock$2.run(DeadLock.java:57) - waiting to lock <0x00000007b9c08580> (a java.lang.Boolean) - locked <0x00000007b9c08c00> (a java.lang.Boolean) at java.lang.Thread.run(Thread.java:748) "Thread-0": at jvm.DeadLock$1.run(DeadLock.java:36) - waiting to lock <0x00000007b9c08c00> (a java.lang.Boolean) - locked <0x00000007b9c08580> (a java.lang.Boolean) at java.lang.Thread.run(Thread.java:748) Found 1 deadlock.
jstat
jstat -<option> <vmid> [<interval> <count>] jstat [-命令选项] [vmid] [间隔时间/毫秒] [查询次数] 1.常用命令参数
命令
作用
-gc
监视堆状况：Eden,S0,S1,老年代,永久代(元空间),压缩类空间,YoungGC,FullGC,GC消耗总时间
-gcutil
与gc基本一致，关注点在百分比
-gccause
与gcutil一致，额外输出上一次GC产生的原因
2.实战
类加载统计:
>jstat -class 2060 Loaded Bytes Unloaded Bytes Time 15756 17355.6 0 0.0 11.29
编译统计
>jstat -compiler 9848 Compiled Failed Invalid Time FailedType FailedMethod 1135 0 0 0.96 0
垃圾回收统计
>jstat -gc 2060 S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT GCT 20480.0 20480.0 0.0 13115.3 163840.0 113334.2 614400.0 436045.7 63872.0 61266.5 0.0 0.0 149 3.440 8 0.295 3.735
堆内存统计
>jstat -gccapacity 2060 NGCMN NGCMX NGC S0C S1C EC OGCMN OGCMX OGC OC MCMN MCMX MC CCSMN CCSMX CCSC YGC FGC 204800.0 204800.0 204800.0 20480.0 20480.0 163840.0 614400.0 614400.0 614400.0 614400.0 0.0 63872.0 63872.0 0.0 0.0 0.0 149 8
新生代垃圾回收统计
>jstat -gcnew 9849 S0C S1C S0U S1U TT MTT DSS EC EU YGC YGCT 10752.0 10752.0 0.0 0.0 15 15 0.0 65536.0 10521.4 0 0.000
新生代内存统计
>jstat -gcnewcapacity 9849 NGCMN NGCMX NGC S0CMX S0C S1CMX S1C ECMX EC YGC FGC 87040.0 1397760.0 87040.0 465920.0 10752.0 465920.0 10752.0 1396736.0 65536.0 0 0
老年代垃圾回收统计
>jstat -gcold 9849 MC MU CCSC CCSU OC OU YGC FGC FGCT GCT 4480.0 774.6 384.0 75.9 175104.0 0.0 0 0 0.000 0.000
老年代内存统计
>jstat -gcoldcapacity 9849 OGCMN OGCMX OGC OC YGC FGC FGCT GCT 175104.0 2796544.0 175104.0 175104.0 0 0 0.000 0.000
元数据空间统计
>jstat -gcmetacapacity 9849 MCMN MCMX MC CCSMN CCSMX CCSC YGC FGC FGCT GCT 0.0 1056768.0 4480.0 0.0 1048576.0 384.0 0 0 0.000 0.000
总垃圾回收统计
>jstat -gcutil 9849 S0 S1 E O M CCS YGC YGCT FGC FGCT GCT 0.00 0.00 16.05 0.00 17.29 19.76 0 0.000 0 0.000 0.000
垃圾回收原因
>jstat -gccause 9849 S0 S1 E O M CCS YGC YGCT FGC FGCT GCT LGCC GCC 0.00 0.00 16.05 0.00 17.29 19.76 0 0.000 0 0.000 0.000 No GC No GC
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