Accessing module internals from bytecode rewriting agent

Jeremy Manson jeremymanson at
Fri May 5 06:39:08 UTC 2017

Thanks, Dalibor.

I know it may sound surprising, but I'm not actually complaining.  I do
understand that most everything we're doing that requires workarounds for
modules is unsupported (with the possible exception of the changes to
instrumentation agents), and we were always doing them at our own risk.
This is far from limited to Xbootclasspath - we have all sorts of hacks,
including, to pick two things at random among many, code that introspects a
Thread's Runnable to pick a good name to report for a thread, and code that
introspects an AbstractInterruptibleChannel to stop the owning thread from
closing the channel when it gets an interrupt.

It's our problem to fix these issues, and I'm unlikely to claim otherwise.
Frankly, it doesn't seem all that difficult to find other ways to
introspect into the JDK - it's just busywork and more awkward than it used
to be.

Mostly, I'm telling you all because I think it makes an interesting case
study - a large Java installation and the issues it faces trying to roll
out JDK 9.

If other installations do the kinds of things that we do, the path to a JDK
9 without lots of add-exports and kill switch options is likely to be slow
and laborious for them.  We're comparatively well situated to do it - we
have our own JDK build and a staffed team to do / help with the migration,
and are likely to roll it out to everyone with the kill switch turned on by
default so that our awful hacks can stay put until we finish fixing them.

(Also, if I were complaining, there would have been a lot of choice things
I would have said that I'm not going to say. :) )


On Thu, May 4, 2017 at 4:35 AM, dalibor topic <dalibor.topic at>

> On 02.05.2017 18:46, Jeremy Manson wrote:
>> People
>> are using Xbootclasspath for a variety of things.
> It's worth keeping in mind when using such options that
> "Non-standard options are general purpose options that are specific to the
> Java HotSpot Virtual Machine, so they are not guaranteed to be supported by
> all JVM implementations, and are subject to change. These options start
> with -X."
> va.html#BABHDABI
> cheers,
> dalibor topic
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