ABCL 1.8.0
Mark Evenson
evenson at panix.com
Fri Oct 30 21:14:06 UTC 2020
> On Oct 30, 2020, at 16:22, Vibhu Mohindra <vibhu.mohindra at gmail.com> wrote:
>
> On 30/10/2020 15:40, Blake McBride wrote:
>> I'd like to add that I care far, far less about "efficiently [implement
>> atomic memory compare and swap operations" than I do about bug fixes and
>> ANSI CL conformance. And it still seems like a lot of work is remaining
>> in those areas.
>>
>> Thanks!
>>
>> Blake
>
>
> How about the following solution? Apologies if it's obviously unworkable.
>
>
> This is the issue:
> https://github.com/armedbear/abcl/issues/92
> which says it requires CAS on a few ABCL functions (svref etc.).
>
> The valuable feature of CAS is that it doesn't require a context switch,
> unlike Java's "synchronized". So let's weaken the requirement above
> (very slightly, if at all) to "anything roughly as lightweight as CAS".
>
> Presumably abcl-2 will use some new JDK11 CAS feature to implement svref
> etc.
> But it could use a "fallback-CAS" implementation when it finds itself on
> an old JRE.
> Say one built upon this (JDK5 feature) as a primitive:
> https://docs.oracle.com/javase/1.5.0/docs/api/java/util/concurrent/atomic/AtomicBoolean.html#compareAndSet(boolean,%20boolean)
> As long as fallback-CAS spins and doesn't switch context, it'll meet the
> weakened requirement above.
>
> No?
>
> Then ABCL-2 will work fast on JDK11 and still almost as fast as that
> even on older versions of Java.
>
> I should probably read up on what specific JDK11 CAS feature abcl-2
> relies upon, that doesn't exist in JDK8. I haven't kept up.
>
> Vibhu
I think I can keep all the current source running on ABCL2, moving new
functionality to some subclass of CONS that implements the CAS semantics I need
in my pursuit of running the [QVM][] on ABCL. Therefore we should be able to fold
existing bugs into fixing abcl-1.8.0 while proceeding to develop abcl2. This
strategy would be somewhat akin to the current mechanism of building support
for Alessio’s ScriptEngine code when the underlying JDK supports it.
None-the-less, it would be advisable for people “stuck” on openjdk8 to start to
evaluate what it would take to run on openjdk11.
Hopefully, we can somehow please everyone.
[QVM]: https://github.com/rigetti/qvm
--
"A screaming comes across the sky. It has happened before but there is nothing
to compare to it now."
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