[e-lang] E-on-Java: How to synchronously access a vat from an
kpreid at attglobal.net
Sat Jun 25 18:50:47 EDT 2005
On Jun 25, 2005, at 15:02, Mark Miller wrote:
> Kevin Reid wrote:
>> Simple description:
>> I have a Java thread from which I want to invoke a function written
>> in E. The Java thread did not start out as an E runner thread.
>> I see two methods:
>> Run the E code in its own default headless Vat/Runner and use some
>> variety of inter-thread communication. The closest thing I've found
>> is Vat#now/1, which does not provide for a return value.
> ...In any case, it's easy to work around this limitation by providing
> a Runnable that stores the return value in an internal field whose
> value you can then access.
Yes, but this would break the inter-vat reference constraints. (What's
a better term for that?) The particular data I have in mind right now
is all Strings, but if it wasn't, this would be unsuitable as a general
I'll do this for now, anyway.
>> I assume I need to use the 'boot-comm' system somehow, which I have
>> not studied. How would I do this?
> If you use this now/1 technique, I don't think you'll need the
> boot-comm system. If you do want to use the boot-comm system, see
> Vat#seed, which is quite hard to use in a thread-safe manner, or
> seedVatAuthor.emaker, which is a thread-safe wrapper for Vat#seed.
Ah. I'd forgotten that Vat#seed did the Right Thing.
If I did this, how would I block the external thread until the result
of a send to the seed-result ref resolves?
>> Set up a Vat running in the original thread. I assume this would
>> require writing a custom Runner that either stubs out
>> eventual-sending or implements it on top of the original thread
>> (which will have its own event loop).
> Yes, it would require a custom Runner and RunnerMgr. It would also
> require adding your RunnerMgr to the Runner#RUNNER_KINDS table.
I thought so. I want to do this such that it works with an unmodified E
distribution. (Of course this could be changed, but it wouldn't work
*now*. And using multiple vats instead of an intra-vat bridge is
arguably the Right Thing.)
>> For this method, how would I set up a Vat on a preexisting Runner?
> Given that you've registered your RunnerMgr on RUNNER_KINDS, you'd use
> the associated runnerKind string as an argument to makeVat.
But in this case, there would not necessarily be only one thread of
this kind - so putting them in RUNNER_KINDS (if that were to become a
mutable table) would not be very capability-structured, as it would
introduce a global namespace. This is really what I meant when I
mentioned assuming only one thread.
Kevin Reid <http://homepage.mac.com/kpreid/>
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