Loom prototype publicly available

Remi Forax forax at univ-mlv.fr
Mon Jul 30 16:13:22 UTC 2018

Hi Ryan,
Continuation is not one shot, you can re-enter it by calling run() again.


----- Mail original -----
> De: "Ryan Schmitt" <rschmitt at pobox.com>
> À: "Ron Pressler" <ron.pressler at oracle.com>
> Cc: "loom-dev" <loom-dev at openjdk.java.net>
> Envoyé: Lundi 30 Juillet 2018 18:03:08
> Objet: Re: Loom prototype publicly available

> 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

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