Removal of SA javascript support

Krystal Mok rednaxelafx at gmail.com
Wed Dec 11 03:26:54 UTC 2019


Hi Chris,

Thanks for the proposal. I used to be one of the few heavy users of jsload
/ jseval in CLHSDB back in the JDK6 to JDK8 era. The way I used to use it
is to quickly prototype new functionality in JS and later bake it into Java
code, and also for exploring heap dumps beneath the existing commands
available in CLHSDB (i.e. the underlying SA API is far more powerful than
the set of commands exposed in HSDB).

I even collected my own library of SA-based JS functions for easy
navigation of Java heap dumps. e.g. this objtree command:
https://gist.github.com/rednaxelafx/1393698#file-objtree-js

I'm sad to see it go but given its current state I'd +1 on the proposal to
remove it now.

Best regards,
Kris

On Tue, Dec 10, 2019 at 6:52 PM Chris Plummer <chris.plummer at oracle.com>
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
>
>
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