[转帖]查看堆内对象的工具：jmap

查看,对象,工具,jmap · 浏览次数 : 0

小编点评

**finalizerinfo 打印等待终结的对象信息** ``` Server compiler detected.JVM version is 25.275-b01 Number of objects pending for finalization: 0 ``` **生成堆存储快照 dump 文件** ``` root@7e2ee19d74ac:/# jmap -dump:format=b,file=heapdump.hprof 1Dumping heap to /heapdump.hprof ...Heap dump file created123 参考：jvm 性能调优工具之 jmap 文章知识点与官方知识档案匹配，可进一步学习相关知识Java技能树首页概览106582 人正在系统学习中 ``` **其他信息** * 进程 ID 1 * 进程名称 "Debugger attached successfully" * 性能调优工具 "jmap"

正文

文章目录

用途

jmap 可以查看堆内对象的信息，生成 java 程序的 dump 文件，甚至可以查看 ClassLoader 的信息以及 finalizer 队列。

命令格式

jmap [option] <pid> # 连接到正在运行的进程
jmap [option] <executable <core> # 连接到核心文件
jmap [option] [server_id@]<remote server IP or hostname> # 连接到远程调试服务

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参数说明：

  1. pid：目标进程的 PID
  2. executable：产生 core dump 的 java 可执行程序
  3. core：被打印信息的 core dump 文件
  4. server-id：可选的唯一 id，如果相同的远程主机上运行了多台调试服务器，用此选项参数标识服务器
  5. remote server IP or hostname：远程调试服务器的 IP 地址或主机名

option 表示选项参数，常见的选项参数如下：

  1. no option：查看进程的内存映像信息
  2. heap：显示堆的详细信息
  3. histo[:live]：显示堆中对象的统计信息
  4. clstats：打印类加载器信息
  5. finalizerinfo：显示在 F-Queue 队列等待 Finalizer 线程执行 finalizer 方法的对象
  6. dump:<dump-options>：生成堆存储快照
  7. F：当 -dump 没有响应时，使用 -dump 或者 -histo 参数，在这个模式下，live 子参数无效
  8. help：帮助信息
  9. J<flag>：指定传递给运行 jmap 的 JVM 的参数

示例

下面我们来看几个使用 jmap 的例子：

注意，由于博主是在 docker 中执行相应的命令，故在新建并启动容器时要加上 --privileged=true --cap-add=SYS_PTRACE 配置，不然在 docker 中无法执行 jmap。

docker run --privileged=true  --cap-add=SYS_PTRACE -d -p 8082:8082 mytest

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一，no option

查看进程的内存映像信息。该命令打印共享对象映射，即打印目标虚拟机中加载的每个共享对象的起始地址、映射大小以及共享对象文件的路径全称。

root@973ba4cf6586:/# jmap 1
Attaching to process ID 1, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.111-b14
0x0000000000400000      6K      /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java
0x00007f99601cb000      75K     /usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/libnio.so
0x00007f99609de000      94K     /usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/libnet.so
0x00007f9960bf6000      38K     /usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/libmanagement.so
0x00007f9975dd3000      34K     /usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/libzip.so
0x00007f9975fdc000      46K     /lib/x86_64-linux-gnu/libnss_files-2.19.so
0x00007f99761e8000      42K     /lib/x86_64-linux-gnu/libnss_nis-2.19.so
0x00007f99763f3000      87K     /lib/x86_64-linux-gnu/libnsl-2.19.so
0x00007f997660b000      30K     /lib/x86_64-linux-gnu/libnss_compat-2.19.so
0x00007f9976813000      191K    /usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/libjava.so
0x00007f9976a43000      74K     /usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/libverify.so
0x00007f9976c56000      31K     /lib/x86_64-linux-gnu/librt-2.19.so
0x00007f9976e5e000      87K     /lib/x86_64-linux-gnu/libgcc_s.so.1
0x00007f9977074000      1026K   /lib/x86_64-linux-gnu/libm-2.19.so
0x00007f9977375000      984K    /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.20
0x00007f9977680000      15805K  /usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/server/libjvm.so
0x00007f9978613000      1697K   /lib/x86_64-linux-gnu/libc-2.19.so
0x00007f99789be000      14K     /lib/x86_64-linux-gnu/libdl-2.19.so
0x00007f9978bc2000      58K     /usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/jli/libjli.so
0x00007f9978dd1000      106K    /lib/x86_64-linux-gnu/libz.so.1.2.8
0x00007f9978fec000      134K    /lib/x86_64-linux-gnu/libpthread-2.19.so
0x00007f9979209000      137K    /lib/x86_64-linux-gnu/ld-2.19.so

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二，heap

显示堆的详细信息。使用该选项可以打印一个堆的摘要信息，包括使用的 GC 算法、堆配置信息和各区域内存使用信息。

root@7e2ee19d74ac:/# jmap -heap 1
Attaching to process ID 1, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.275-b01

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 = 9502720 (9.0625MB)

used     = 7132664 (6.802238464355469MB)

free     = 2370056 (2.2602615356445312MB)

75.05918305495689% used

Eden Space:

capacity = 8454144 (8.0625MB)

used     = 6412176 (6.1151275634765625MB)

free     = 2041968 (1.9473724365234375MB)

75.84654342296511% used

From Space:

capacity = 1048576 (1.0MB)

used     = 720488 (0.6871109008789062MB)

free     = 328088 (0.31288909912109375MB)

68.71109008789062% used

To Space:

capacity = 1048576 (1.0MB)

used     = 0 (0.0MB)

free     = 1048576 (1.0MB)

0.0% used

tenured generation:

capacity = 20971520 (20.0MB)

used     = 13845136 (13.203750610351562MB)

free     = 7126384 (6.7962493896484375MB)

66.01875305175781% used


14836 interned Strings occupying 1393776 bytes.


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三，histo[:live]

显示堆中对象的统计信息，包括了每个 Java 类、对象数量、内存大小(单位：字节)、完全限定的类名。打印的虚拟机内部的类名称将会带有一个 * 前缀。如果指定了 live 子选项，则只计算活动的对象。

root@7e2ee19d74ac:/# jmap -histo:live 1
.
.
.
.
2481:             1             16  sun.reflect.generics.tree.ByteSignature
2482:             1             16  sun.reflect.generics.tree.CharSignature
2483:             1             16  sun.reflect.generics.tree.DoubleSignature
2484:             1             16  sun.reflect.generics.tree.FloatSignature
2485:             1             16  sun.reflect.generics.tree.IntSignature
2486:             1             16  sun.reflect.generics.tree.LongSignature
2487:             1             16  sun.reflect.generics.tree.ShortSignature
2488:             1             16  sun.reflect.generics.tree.VoidDescriptor
2489:             1             16  sun.security.provider.NativePRNG
2490:             1             16  sun.util.calendar.Gregorian
2491:             1             16  sun.util.locale.provider.AuxLocaleProviderAdapter$NullProvider
2492:             1             16  sun.util.locale.provider.CalendarDataUtility$CalendarWeekParameterGetter
2493:             1             16  sun.util.locale.provider.SPILocaleProviderAdapter
2494:             1             16  sun.util.locale.provider.TimeZoneNameUtility$TimeZoneNameGetter
2495:             1             16  sun.util.resources.LocaleData
2496:             1             16  sun.util.resources.LocaleData$LocaleDataResourceBundleControl
Total        235864       12512632

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四，clstats

打印类加载器信息。对于每个类加载器而言，它的名称、活跃度、地址、父类加载器、它所加载的类的数量和大小都会被打印。此外，包含的字符串数量和大小也会被打印。

root@7e2ee19d74ac:/# jmap -clstats 1
Attaching to process ID 1, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.275-b01
finding class loader instances ..done.
computing per loader stat ..done.
please wait.. computing liveness..........................................................................liveness analysis may be inaccurate ...
class_loader    classes bytes   parent_loader   alive?  type

<bootstrap>     2026    3553710   null          live    <internal>

0x00000000ed382638      1       1471    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed78ed78      1       880     0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed299328      1       1473    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed03af80      1       1471    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed2999a0      1       1471    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed33deb8      1       1473    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed8bba80      1       1472    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed7d3870      1       1472    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ecdecad0      0       0         null          live    sun/misc/Launcher\(ExtClassLoader<span class="token annotation punctuation">@0x000000010000fd00</span>
<span class="token number">0x00000000ed78ebe8</span>      <span class="token number">1</span>       <span class="token number">880</span>     <span class="token number">0x00000000ecdbd518</span>      dead    sun<span class="token operator">/</span>reflect<span class="token operator">/</span>DelegatingClassLoader<span class="token annotation punctuation">@0x000000010000a0a0</span>
<span class="token number">0x00000000ed2994b8</span>      <span class="token number">1</span>       <span class="token number">1473</span>    <span class="token number">0x00000000ecdbd518</span>      dead    sun<span class="token operator">/</span>reflect<span class="token operator">/</span>DelegatingClassLoader<span class="token annotation punctuation">@0x000000010000a0a0</span>
<span class="token number">0x00000000ed23ecb0</span>      <span class="token number">1</span>       <span class="token number">1472</span>      null          dead    sun<span class="token operator">/</span>reflect<span class="token operator">/</span>DelegatingClassLoader<span class="token annotation punctuation">@0x000000010000a0a0</span>
<span class="token number">0x00000000ed33e2a0</span>      <span class="token number">1</span>       <span class="token number">1471</span>    <span class="token number">0x00000000ecdbd518</span>      dead    sun<span class="token operator">/</span>reflect<span class="token operator">/</span>DelegatingClassLoader<span class="token annotation punctuation">@0x000000010000a0a0</span>
<span class="token number">0x00000000ed3e7e28</span>      <span class="token number">1</span>       <span class="token number">1472</span>      null          dead    sun<span class="token operator">/</span>reflect<span class="token operator">/</span>DelegatingClassLoader<span class="token annotation punctuation">@0x000000010000a0a0</span>
<span class="token number">0x00000000ed298db0</span>      <span class="token number">1</span>       <span class="token number">880</span>     <span class="token number">0x00000000ecdbd518</span>      dead    sun<span class="token operator">/</span>reflect<span class="token operator">/</span>DelegatingClassLoader<span class="token annotation punctuation">@0x000000010000a0a0</span>
<span class="token number">0x00000000ed33dd28</span>      <span class="token number">1</span>       <span class="token number">1473</span>    <span class="token number">0x00000000ecdbd518</span>      dead    sun<span class="token operator">/</span>reflect<span class="token operator">/</span>DelegatingClassLoader<span class="token annotation punctuation">@0x000000010000a0a0</span>
<span class="token number">0x00000000ed5095f0</span>      <span class="token number">1</span>       <span class="token number">1472</span>    <span class="token number">0x00000000ecdbd518</span>      dead    sun<span class="token operator">/</span>reflect<span class="token operator">/</span>DelegatingClassLoader<span class="token annotation punctuation">@0x000000010000a0a0</span>
<span class="token number">0x00000000ed78e8d8</span>      <span class="token number">1</span>       <span class="token number">1472</span>      null          dead    sun<span class="token operator">/</span>reflect<span class="token operator">/</span>DelegatingClassLoader<span class="token annotation punctuation">@0x000000010000a0a0</span>
<span class="token number">0x00000000ed299008</span>      <span class="token number">1</span>       <span class="token number">1473</span>    <span class="token number">0x00000000ecdbd518</span>      dead    sun<span class="token operator">/</span>reflect<span class="token operator">/</span>DelegatingClassLoader<span class="token annotation punctuation">@0x000000010000a0a0</span>
<span class="token number">0x00000000ed33e110</span>      <span class="token number">1</span>       <span class="token number">1473</span>    <span class="token number">0x00000000ecdbd518</span>      dead    sun<span class="token operator">/</span>reflect<span class="token operator">/</span>DelegatingClassLoader<span class="token annotation punctuation">@0x000000010000a0a0</span>
<span class="token number">0x00000000ed43d0e0</span>      <span class="token number">1</span>       <span class="token number">1471</span>    <span class="token number">0x00000000ecdbd518</span>      dead    sun<span class="token operator">/</span>reflect<span class="token operator">/</span>DelegatingClassLoader<span class="token annotation punctuation">@0x000000010000a0a0</span>
<span class="token number">0x00000000ed299580</span>      <span class="token number">1</span>       <span class="token number">1473</span>    <span class="token number">0x00000000ecdbd518</span>      dead    sun<span class="token operator">/</span>reflect<span class="token operator">/</span>DelegatingClassLoader<span class="token annotation punctuation">@0x000000010000a0a0</span>
<span class="token number">0x00000000eced1140</span>      <span class="token number">0</span>       <span class="token number">0</span>       <span class="token number">0x00000000ecdbd8b0</span>      live    java<span class="token operator">/</span>util<span class="token operator">/</span>ResourceBundle\)RBClassLoader@0x00000001000b64b0

0x00000000ed299198      1       1473    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed691fd8      1       1471    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed33df80      1       1473    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed43d270      1       1472    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed8bafb8      1       1472    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed382700      1       1471    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed78ee40      1       1474    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed299710      1       1473    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed03abb8      1       1472    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed23c518      1       880     0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed299a68      1       880     0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ecdbd518      3662    5648946 0x00000000ecdbd8b0      live    org/springframework/boot/loader/LaunchedURLClassLoader@0x0000000100060a10

0x00000000ed33ddf0      1       1474      null          dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed748b30      1       1472    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed7d3938      1       880       null          dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed382470      1       1476    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed78ecb0      1       880     0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed299260      1       1473    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed0cddc0      1       1472    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed15e2d8      1       1472      null          dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed298e78      1       880     0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed33dc60      1       880     0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed7d3828      1       1472      null          dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed78eb20      1       880     0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed2993f0      1       1471    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed2211f8      1       1472      null          dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed3e7d60      1       1472    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed6f79b0      0       0       0x00000000ecdbd518      live    org/springframework/boot/web/embedded/tomcat/TomcatEmbeddedWebappClassLoader@0x00000001003cec70

0x00000000ed299648      1       1471    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed298f40      1       1476    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ecdbd8b0      38      63472   0x00000000ecdecad0      live    sun/misc/Launcher$AppClassLoader@0x000000010000f958

0x00000000ed33e1d8      1       1471    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed43d1a8      1       1471    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed4c6ea0      1       1505      null          dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed3827c8      1       1471    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed78ef08      1       880     0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed2997d8      1       1473    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed03a7f0      1       1471    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed2990d0      1       1471    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed691f10      1       1473    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed33e048      1       1473    0x00000000ecdbd518      dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0

0x00000000ed7d3a00      1       880       null          dead    sun/reflect/DelegatingClassLoader@0x000000010000a0a0


total = 66      5786    9347389     N/A         alive=6, dead=60            N/A


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五，finalizerinfo

打印等待终结的对象信息。

root@7e2ee19d74ac:/# jmap -finalizerinfo 1
Attaching to process ID 1, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.275-b01
Number of objects pending for finalization: 0

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可见等候回收的对象为0个。

六，dump:<dump-options>

生成堆存储快照 dump 文件，以 hprof 二进制格式存储 Java 堆到指定 filename 的文件中，如果你指定 live 子选项，堆中只有活动的对象会被存储。

执行这个命令，JVM 会将整个 heap 的信息 dump 写入到一个文件，如果 heap 很大的话，这个过程可能非常耗时，而且会在执行的过程中暂停应用。

root@7e2ee19d74ac:/# jmap -dump:format=b,file=heapdump.hprof 1
Dumping heap to /heapdump.hprof ...
Heap dump file created

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参考：jvm 性能调优工具之 jmap

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