vmtool

vmtool uses the JVMTI to support getInstances in jvm and forceGc.

getInstances

$ vmtool --action getInstances --className java.lang.String --limit 10
@String[][
    @String[com/taobao/arthas/core/shell/session/Session],
    @String[com.taobao.arthas.core.shell.session.Session],
    @String[com/taobao/arthas/core/shell/session/Session],
    @String[com/taobao/arthas/core/shell/session/Session],
    @String[com/taobao/arthas/core/shell/session/Session.class],
    @String[com/taobao/arthas/core/shell/session/Session.class],
    @String[com/taobao/arthas/core/shell/session/Session.class],
    @String[com/],
    @String[java/util/concurrent/ConcurrentHashMap$ValueIterator],
    @String[java/util/concurrent/locks/LockSupport],
]

Through the --limit parameter, you can limit the number of return values to avoid pressure on the JVM when obtaining large data. The default value of limit is 10.

Specify classloader name

vmtool --action getInstances --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader --className org.springframework.context.ApplicationContext

Specify classloader hash

The classloader that loads the class can be found through the sc command.

$ sc -d org.springframework.context.ApplicationContext
 class-info org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext
 code-source file:/private/tmp/demo-arthas-spring-boot.jar!/BOOT-INF/lib/spring-boot-1.5.13.RELEASE.jar!/
 name org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext
...
 class-loader +-org.springframework.boot.loader.LaunchedURLClassLoader@19469ea2
                     +-sun.misc.Launcher$AppClassLoader@75b84c92
                       +-sun.misc.Launcher$ExtClassLoader@4f023edb
 classLoaderHash 19469ea2

Then use the -c/--classloader parameter to specify:

vmtool --action getInstances -c 19469ea2 --className org.springframework.context.ApplicationContext

Specify the number of expanded layers of returned results

The return result of the getInstances action is bound to the instances variable, which is an array.

The expansion level of the result can be specified by the -x/--expand parameter, the default value is 1.

vmtool --action getInstances -c 19469ea2 --className org.springframework.context.ApplicationContext -x 2

Execute expression

The return result of the getInstances action is bound to the instances variable, which is an array. The specified expression can be executed through the --express parameter.

vmtool --action getInstances --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader --className org.springframework.context.ApplicationContext --express'instances[0].getBeanDefinitionNames()'

Force GC

vmtool --action forceGc

  • Use the vmoption command to dynamically turn on the PrintGC option.