[1]:
http://hg.openjdk.java.net/jdk/jdk/file/c71ec1f09f21/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/CommandProcessor.java#l246
- Kris
On Tue, Dec 10, 2019 at 9:33 PM Yasumasa Suenaga
<suen...@oss.nttdata.com <mailto:suen...@oss.nttdata.com>> wrote:
Hi Chris,
It's a sad proposal, but I agree with you. To maintain SA in JS
is difficult since Jigsaw.
However I want SA to implement pluggable feature.
I use custom script to list compiled codes in CodeCache.
I guess other troubleshooters also want similar feature (via
jsload) in future if they encounter JVM crash.
Thanks,
Yasumasa
On 2019/12/11 11:52, Chris Plummer wrote:
> Hi,
>
> I like to propose the removal of SA javascript support. Few
people even realize this support exists, and hopefully even fewer
are using it since I'd like to remove it. Since I'm new to this
myself, let me first explain what I know about it's existence, and
then explain why I want to remove it.
>
> If you run "jhsdb clhsdb", there are jsload and jseval
commands. Don't look for them in anything post JDK 8. I'll explain
why later. jsload is used to load a javascript file. In that file
you can register new clhsdb commands that are written in
javascript. You can also evaluate javascript using the jseval
command. Some of this is explained in [1], which is the only place
I can find any reference to this support. It does not appear to be
officially supported, nor is there any oracle provided documentation.
>
> There also appear to be a few clhsdb commands that are
written in javascript. Doing a grep for "registerCommand" in sa.js
shows the following:
>
> registerCommand("class", "class name", "jclass");
> registerCommand("classes", "classes", "jclasses");
> registerCommand("dumpclass", "dumpclass { address | name }
[ directory ]", "dclass");
> registerCommand("dumpheap", "dumpheap [ file ]", "dumpHeap");
> registerCommand("mem", "mem address [ length ]", "printMem");
> registerCommand("sysprops", "sysprops", "sysProps");
> registerCommand("whatis", "whatis address", "printWhatis");
>
> Once again, don't go looking for these in anything newer
than JDK8. You won't find them. Again the only documentation I can
fine is [1].
>
> The other use of Javascript is the SOQL command (Simple
Object Query Language), a tool used to query the heap, and also the
JSDB command. The only SOQL documentation I could find is the blog
reference [2]. I could not find HSDB documentation, but I believe
is is a javascript support for looking at hotspot. So once again,
neither of these seem to be officially supported or documented.
>
> The real purpose of the email is to propose removal of this
support. Here are the reasons:
>
> (1) It's broken, and has been since 9. See [3]. This is why
you don't see the javascript related commands in clhsdb. Javascript
fails to initialize, so none of the javascript related commands are
registered.
> (2) Nashorn is deprecated and will be removed eventually.
> (3) We have very little understanding of the javascript
support.
> (4) No resources to work on it (unless there is a community
volunteer).
> (5) Very questionable value (lack of users). The fact this
support has been broken since JDK 9 and no bug was filed until I
did so this week is a good indication of that. Another is that
there are no other SA Javascript related bugs filed. Lastly, the
lack of any official documentation and only minimal mention of it
on the web is another good indication of it's (lack of) value.
>
> Also, regarding the 7 commands listed above that would be
lost (but currently don't work now anyway), if they are really
wanted, they could be implemented in java instead of javascript.
>
> I'd like to remove javascript support in two steps. The
first is simply disable the clhsdb code that tries to initialize
the javascript support. I'd like to do this in 14 (actually as soon
as possible). I'd like to actually do this now even if we decide to
keep javascript support and eventually fix it because it will get
rid of the warning you see whenever you attach from clhsdb:
>
> Warning! JS Engine can't start, some commands will not
be available.
>
> This warning will become more of an issue for the clhsdb
tests after I push [4] because then you will also see the full
stacktrace for the underlying exception that caused the Javascript
to fail to start. Besides being unnecessary noise in passing test
cases, it can also be misleading in any test that fails because the
exception will be unrelated to the failure. This is actually what
got me going down this path of what the javascript support is all
about.
>
> The next step would be to strip out all Javascript related
code, including the SOQL and JSDB tools. This would be done in 15.
>
> Please let me know what you think.
>
> thanks,
>
> Chris
>
> [1]
https://cr.openjdk.java.net/~minqi/6830717/raw_files/new/agent/doc/clhsdb.html
> [2]
http://javatroubleshooting.blogspot.com/2015/12/serviceability-agent-part-3.html
> [3] https://bugs.openjdk.java.net/browse/JDK-8235594
> [4] https://bugs.openjdk.java.net/browse/JDK-8234277
>
