RFR: 8262504: Some CLHSDB command cannot know they run on remote debugger

[Yasumasa Suenaga]

On Wed, 3 Mar 2021 23:42:31 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

> This section seems to be the key to your changes, but I have to admit that I don't follow how it all ties in together. Maybe you can explain the overall structure of the Tool subclasses to help explain. They seem to be overloaded with modes that make it hard to follow all the logic. For example, you've added the `Tool(HotSpotAgent agent)` constructor, and we already have `Tool()` and `Tool(JVMDebugger d)`. It's unclear to me what the use case is for each. Also, we have about 10 subclasses of Tool. Why do only `PMap` an `PStack` need this new constructor.

All of traditional serviceability commands (jstack, jmap, etc...) seem to extend `Tool` because it has a function to parse commandline args and to attach debuggee commonly.
`Tool` supports several attach mechanism: `Tool()` supports attach debuggee manually, `Tool(JVMDebugger)` supports attach debuggee via available `JVMDegbugger`. `HotSpotAgent` communicates to debugee, so `Tool` would create its instance. Thus I added `Tool(HotSpotAgent)` to use available remote debug server.

AFAICS only `PMap` and `PStack` do not support remote debug server, so I changed for them.
(I plan to support `pmap` and `pstack` when we attach remote debug server, so it is important to know debuggee type.)

> BTW, looking at Tool and its subclasses has made me realize we have a whole other area of historical tool baggage, similar to what we are discussing with CLHSDB and HSDB. My guess is all these tool subclasses used to be invoked directly from the java command line. Now they are all hidden behind `jhsdb` subcommands, but still carry the old java command line support. In addition, when adding `jhsdb` and it's subcommands, it looks like there was an effort to mimic the existing Attach API commands like jmap and jinfo, so the SA versions of these commands have multiple modes which invoke different Tool subclasses. For example, `jhdsb jmap` alone can invoke the ClassLoaderStats, FinalizerInfo, ObjectHistogram, PMap, and HeapSummary tools, in addition to dumping the heap graph in HProf or GXL format. I think things would have been simpler and cleaner if each of these were made separate `jhsdb` subcommands, but it's probably too late for that. I suppose we could deprecate the existing sub-
 commands and add all these new sub-commands, but that will just make things harder for us until the old commands are eventually removed, which might never happen.

I agree with you it is too late to happen.
As I commented in https://github.com/openjdk/jdk/pull/2773#issuecomment-790203478 , we can do simplify for them as possible. For example, we can remove `main()` and related methods (e.g. showing usage) from them. If we can remove commandline support from all tool classes, It might help a little to maintain.

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PR: https://git.openjdk.java.net/jdk/pull/2766