Re: ABCL 1.8.0

> On Oct 30, 2020, at 16:22, Vibhu Mohindra <[email protected]> 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."