RFR: 8287437: Temporarily disable Continuations::enabled() for platforms which don't have an implementation, yet

[Alan Bateman]

On Fri, 27 May 2022 11:56:52 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> Hello,
> 
> I'd like to disable `Continuations::enabled()` for platforms, which don't support Loom, yet. This enables working on Panama which is also controlled by `--enable-preview`.
> 
> I'm proposing this for all platforms which have an unresolved porting issue here:
> [JDK-8284161](https://bugs.openjdk.java.net/browse/JDK-8284161)
> 
> Please review and provide feedback if this makes sense for your platform.

> I'd probably just define the platforms where Loom _is_ implemented: `AMD64` and `AARCH64`.

I think that would be better too.

I hope to propose changes soon that adds an alternative virtual thread implementation that is backed by a platform thread (1-1 mapping). This clearly won't scale but it should be enough to pass conformance tests on platforms that might not have VM support for continuations for some time. Part of that needs to separate "supported by VM" from "preview features are enabled" as it has to be surfaced to the library code so it can choose the implementation.

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PR: https://git.openjdk.java.net/jdk/pull/8919