jinfo

2023-08-18 20:10| 来源: 网络整理| 查看: 265

一点睛

jinfo(Configuration Info for Java)：查看虚拟机配置参数信息，也可用于调整虚拟机的配置参数。

在很多情况卡，Java 应用程序不会指定所有的 Java 虚拟机参数。而此时，开发人员可能不知道某一个具体的 Java 虚拟机参数的默认值。在这种情况下，可能需要通过查找文档获取某个参数的默认值。这个查找过程可能是非常艰难的。但有了 jinfo 工具，开发人员可以很方便地找到 Java 虚拟机参数的当前值。

基本使用语法为：jinfo [options] pid

说明：java 进程 ID 必须要加上

选项

选项说明

no option

输出全部的参数和系统属性

-flag name

输出对应名称的参数

-flag [+-]name

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

设定对应名称的参数

-flags

输出全部的参数

-sysprops

输出系统属性

官方帮助文档：

https://docs.oracle.com/en/java/javase/11/tools/jinfo.html

二实战 1 代码 package chaper02; import java.util.Scanner; public class ScannerTest { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); String info = scanner.next(); } } 2 jinfo -sysprops PID——可以查得由System.getProperties()取得的参数

F:\svn\19_byzb_back\branches\JVMDemo3>jinfo -sysprops 1552

Attaching to process ID 1552, please wait...

Debugger attached successfully.

Server compiler detected.

sun.desktop = windows

sun.cpu.isalist = amd64

3 jinfo -flags PID——查看曾经赋过值的一些参数

F:\svn\19_byzb_back\branches\JVMDemo3>jinfo -flags 3528

Attaching to process ID 3528, please wait...

Debugger attached successfully.

Server compiler detected.

JVM version is 25.251-b08

Non-default VM flags: -XX:CICompilerCount=4 -XX:InitialHeapSize=62914560 -XX:MaxHeapSize=62914560 -XX:MaxNewSize=20971520 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=20971520 -XX:OldSize=41943040 -XX:SurvivorRatio=8 -XX:+UseCompressedC

lassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC

Command line: -Xms60m -Xmx60m -XX:SurvivorRatio=8 -javaagent:D:\ProgramFiles\JetBrains\IDEA\lib\idea_rt.jar=53644:D:\ProgramFiles\JetBrains\IDEA\bin -Dfile.encoding=UTF-8

4 jinfo -flag name PID——查看某个 java 进程的具体参数的值

F:\svn\19_byzb_back\branches\JVMDemo3>jinfo -flag UseParallelGC 5208

-XX:+UseParallelGC

F:\svn\19_byzb_back\branches\JVMDemo3>jinfo -flag UseSerialGC 5208

-XX:-UseSerialGC

F:\svn\19_byzb_back\branches\JVMDemo3>jinfo -flag MaxHeapSize 5208

-XX:MaxHeapSize=104857600

5 查看被标记为 manageable 的参数

F:\svn\19_byzb_back\branches\JVMDemo3>java -XX:+PrintFlagsFinal -version|find "manageable"

intx CMSAbortablePrecleanWaitMillis = 100 {manageable}

intx CMSTriggerInterval = -1 {manageable}

intx CMSWaitDuration = 2000 {manageable}

bool HeapDumpAfterFullGC = false {manageable}

bool HeapDumpBeforeFullGC = false {manageable}

bool HeapDumpOnOutOfMemoryError = false {manageable}

ccstr HeapDumpPath = {manageable}

uintx MaxHeapFreeRatio = 100 {manageable}

uintx MinHeapFreeRatio = 0 {manageable}

bool PrintClassHistogram = false {manageable}

bool PrintClassHistogramAfterFullGC = false {manageable}

bool PrintClassHistogramBeforeFullGC = false {manageable}

bool PrintConcurrentLocks = false {manageable}

bool PrintGC = false {manageable}

bool PrintGCDateStamps = false {manageable}

bool PrintGCDetails = false {manageable}

bool PrintGCID = false {manageable}

bool PrintGCTimeStamps = false {manageable}

java version "1.8.0_251"

Java(TM) SE Runtime Environment (build 1.8.0_251-b08)

Java HotSpot(TM) 64-Bit Server VM (build 25.251-b08, mixed mode)

6 jinfo -flag [+-]name——开启或关闭对应名称的参数

F:\svn\19_byzb_back\branches\JVMDemo3>jinfo -flag PrintGCDetails 5209

-XX:-PrintGCDetails

F:\svn\19_byzb_back\branches\JVMDemo3>jinfo -flag +PrintGCDetails 5209

F:\svn\19_byzb_back\branches\JVMDemo3>jinfo -flag PrintGCDetails 5209

-XX:+PrintGCDetails

7 jinfo -flag name = value —— 设置对应名称的参数

F:\svn\19_byzb_back\branches\JVMDemo3>jinfo -flag MaxHeapFreeRatio 5209

-XX:MaxHeapFreeRatio=100

F:\svn\19_byzb_back\branches\JVMDemo3>jinfo -flag MaxHeapFreeRatio=90 5209

F:\svn\19_byzb_back\branches\JVMDemo3>jinfo -flag MaxHeapFreeRatio 5209

-XX:MaxHeapFreeRatio=90

三拓展 1 java -XX:+PrintFlagsInitial 查看所有 JVM 参数启动的初始值

[Global flags]

intx ActiveProcessorCount = -1 {product}

uintx AdaptiveSizeDecrementScaleFactor = 4 {product}

uintx AdaptiveSizeMajorGCDecayTimeScale = 10 {product}

uintx AdaptiveSizePausePolicy = 0 {product}

...

2 java -XX:+PrintFlagsFinal 查看所有 JVM 参数的最终值

[Global flags]

intx ActiveProcessorCount = -1 {product}

...

intx CICompilerCount := 4 {product}

uintx InitialHeapSize := 333447168 {product}

uintx MaxHeapSize := 1029701632 {product}

uintx MaxNewSize := 1774714880 {product}

3 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

-XX:InitialHeapSize=332790016 -XX:MaxHeapSize=5324640256 -XX:+PrintCommandLineFlags -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC

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