On Oct 30, 2020, at 16:22, Vibhu Mohindra vibhu.mohindra@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/At...) 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