Loom prototype publicly available

[Ryan Schmitt]

This is a fascinating prototype. Would it be correct to describe Loom's
continuations as "one-shot" continuations? Should it be possible to
implement the `amb` operator on this prototype?

On Fri, Jul 27, 2018 at 10:51 AM, Ron Pressler <ron.pressler at oracle.com>
wrote:

> Hi.
>
> You can now build and try our initial Loom prototype.
>
>         $ hg clone http://hg.openjdk.java.net/loom/loom
>         $ cd loom
>         $ hg update -r fibers
>         $ sh configure
>         $ make images
>
> (Note that you must switch to the fibers branch)
>
> - Supported platforms: Mac and Linux on x86-64
> - Tested GCs: Parallel and G1
> - Supported compilers: C1, C2, Graal
> - Missing features: JVM TI (fiber debugging), fiber/continuation
> serialization
>
> Work on tail calls has not yet begun.
>
> Current status will be tracked in a wiki page we will set up soon.
>
> The fibers API is in the java.lang.Fiber class, and is minimal at this
> stage.
> Thread locals should work as expected (and be associated with the fiber),
> and
> calls to Thread.currentThread() would return a consistent result, so a lot
> of
> existing code should work. Most relevant IO operations, as well as
> java.util.concurrent constructs, Thread.sleep etc. will now result in the
> fiber
> — rather than the underlying kernel thread — being blocked.
>
> Object.wait() would still block the underlying kernel thread, as would
> trying to
> park a fiber while a native monitor is held or a native method is on the
> stack.
>
> The current implementation performs a full stack copy by default. To
> experiment
> with the lazy-copying solution I described in a previous email, add
> `-XX:+UnlockExperimentalVMOptions -XX:+UseNewCode`, but note that in that
> mode
> exceptions thrown inside continuations may not work (probably crash the
> VM) and
> stack traces would be missing frames.
>
> This is an initial prototype made to be simple to implement so we could
> experiment with different APIs, compatibility etc.. Performance,
> therefore, is
> far from stellar. Designing a good API and writing an implementation with
> good
> performance are our top priorities.
>
> You’re welcome to try the prototype and share your impressions here. On
> Monday,
> we’ll present Loom at JVMLS, and more updates will follow.
>
>
> Ron
>
>
>
>