jcmd supports VMID query via Java process display name #1301
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docs/tool_jcmd.md
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| - `<vmid>` is the Attach API virtual machine identifier for the Java™ VM process. This ID is often, but not always, the same as the operating system *process ID*. One example where the ID might be different is if you specified the system property `-Dcom.ibm.tools.attach.id` when you started the process. You can use the [`jps`](tool_jps.md) command to find the VMID. | |||
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| You can also specify the full or partial Java process display name instead of the VMID. The `jcmd` tool finds the corresponding VMID of the display name and runs the `jcmd` command. | |||
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What is a Java process display name, is this defined somewhere?
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No, not specifically. But, I can see display name mentioned in https://eclipse.dev/openj9/docs/dcomibmtoolsattachdisplayname/. Is this same as Java process display name? Could you specify any other definition that I should add? Thanks!
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Jason pls help clear this up. The linked topic https://eclipse.dev/openj9/docs/dcomibmtoolsattachdisplayname/ could use more explanation of what the display name is, what is the default, what it's used for.
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Jcmd or Jcmd -l lists current java processes recognized by this utility, the list comes with two columns, one is VMID which usually is the process id, and the other is the display name.
The display name for a virtual machine could be specified via a system property com.ibm.tools.attach.displayName as per https://eclipse.dev/openj9/docs/dcomibmtoolsattachdisplayname/, otherwise it is the main class name along with the application arguments.
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So basically the default display name is the entire java command line. I don't know that sun.java.command is documented so better not to mention it.
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Replace it with the main class name along with the application arguments.
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JcmdorJcmd -llists current java processes recognized by this utility, the list comes with two columns, one is VMID which usually is the process id, and the other is the display name.The display name for a virtual machine could be specified via a system property
com.ibm.tools.attach.displayNameas per https://eclipse.dev/openj9/docs/dcomibmtoolsattachdisplayname/, otherwise it is the main class name along with the application arguments.
@JasonFengJ9 - Is it "The display name for a virtual machine" or "The display name for the Java VM process", or "The display name for the Attach API virtual machine" or "The display name for the target virtual machine on which the jcmd command must run."?
- is
-l, one of the options available forjcmdin addition to-Jand-h? - Also, do both
jcmdandjcmd -llist the current java processes recognized by this utility? i.e. even if we don't specify the-loption, will it still list the current java processes?
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Is it "The display name for a virtual machine" or "The display name for the Java VM process", or "The display name for the Attach API virtual machine" or "The display name for the target virtual machine on which the jcmd command must run."?
When Jcmd or other AttachAPI utilities list the currently running Java processes, the display name refers to the target Java process that could be attached by Jcmd.
is -l, one of the options available for jcmd in addition to -J and -h?
Correct.
Also, do both jcmd and jcmd -l list the current java processes recognized by this utility? i.e. even if we don't specify the -l option, will it still list the current java processes?
Yes, -l is the default option.
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Is the following correct? Especially this part jcmd [pid | main-class] command. I saw this mentioned in eclipse-openj9/openj9#19045 (comment)
The display name for a target VM is specified either through a system property
com.ibm.tools.attach.displayName, or by specifying the main class name along with the application arguments -jcmd [pid | main-class] command.
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The main-class (along with application arguments) are the default display name if no system property com.ibm.tools.attach.displayName was set.
Suggest changing to something like following:
The display name for a target VM is specified through a system property com.ibm.tools.attach.displayName, or by default the main class name along with the application arguments - jcmd [pid | main-class] command.
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@JasonFengJ9 @pshipton - I have updated the documents. Please check and confirm. Thanks! |
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Can we pls add the information describing the default display name into the https://eclipse.dev/openj9/docs/dcomibmtoolsattachdisplayname/ topic. |
In the existing content, default is described as "The command line invocation used to start the application", which doesn't make sense. Can I replace this line with "Main class name along with the application arguments"? Will that be correct? Does the -Dcom.ibm.tools.attach.displayName system property have a specific default value of its own? Or is it just that if the nothing is specified in the system property then the display name is set as "Main class name along with the application arguments and not that the system property is defaulted to "Main class name along with the application arguments"? Thanks! |
Works for me.
Yes |
Then, that means "Main class name along with the application arguments" is not the default value of |
I agree. I didn't even notice the default value column described the behavior until you mentioned it. |
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@pshipton - I have made the changes. Please check and confirm. Thanks! |
docs/tool_jcmd.md
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| You can specify the display name for a target VM through the [`com.ibm.tools.attach.displayName`](dcomibmtoolsattachdisplayname.md) system property. If the display name is not set through the system property, then the main class name along with the application arguments is set as the default display name. The command syntax is as follows: | ||
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| jcmd [pid | main-class] command |
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I still don't understand the purpose of this. The jcmd command syntax is already shown on line 32 as jcmd <vmid | display name | 0> <arguments>, why do we want to state it again here, in a paragraph describing the display name, and using different parameter names, ie. pid vs vmid, main-class vs display name, command vs arguments.
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@pshipton - I have made the change. Thanks! |
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@JasonFengJ9 any further concerns? |
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@pshipton - Please check and confirm. Thanks! |
eclipse-openj9#1292 Updated the related topics with the change in jcmd VMID query behavior. Incorporated the feedback Closes eclipse-openj9#1292 Signed-off-by: Sreekala Gopakumar <[email protected]>
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#1292
Updated the related topics with the change in jcmd VMID query behavior
Closes #1292
Signed-off-by: Sreekala Gopakumar [email protected]