[
Date Prev][
Date Next][
Thread Prev][
Thread Next][
Date Index][
Thread Index]
[
List Home]
|
Re: [eclipse-incubator-e4-dev] Asynchronous Infrastructure (was: EFS, ECF and asynchronous)
|
The asynchronous viewer framework in debug was designed such that clients
could implement futures using jobs, but did not require clients to use
jobs. (And the debug platform itself uses jobs to implement its futures).
Perhaps if the job framework was extensible such that clients could
provide their own implementation of job scheduling/execution, then jobs
would suffice.
Darin
John Arthorne/Ottawa/IBM@IBMCA
Sent by: eclipse-incubator-e4-dev-bounces@xxxxxxxxxxx
10/31/2008 09:07 AM
Please respond to
E4 developer list <eclipse-incubator-e4-dev@xxxxxxxxxxx>
To
E4 developer list <eclipse-incubator-e4-dev@xxxxxxxxxxx>
cc
Subject
Re: [eclipse-incubator-e4-dev] Asynchronous Infrastructure (was: EFS, ECF
and asynchronous)
There doesn't seem to be much difference between the future construct you
describe and the Job API. You can attach listeners to jobs which seems to
be the same as your Callback mechanism. Future.waitFor() is the same as
Job.join(), and Future.get() is similar to Job.getResult(). I did actually
have futures in mind when designing the jobs API, with the job's "result"
being the payload returned from the asynchronous operation. I initially
made this result of type Object so clients could pass back whatever return
value they wanted. I then perhaps mistakenly switched the result type to
IStatus, thinking that clients could return sub-types of Status containing
any result object they wanted. This is why I specified almost nothing for
the return value of Job#run and Job#getResult, leaving it as a mechanism
for clients to communicate whatever they want back to the caller. In
reality it didn't end up being used this way, because people fell into the
common coding patterns around IStatus and just returned the usual OK/ERROR
results.
So, I'm wondering if there's something fundamental missing from Jobs that
makes these asynchronous coding patterns difficult, and is there some
incremental improvement we can make to Jobs to make it as expressive and
useful as your Future construct? If not, the org.eclipse.core.jobs bundle
could still perhaps be a home for such an API, since it obviously needs a
backing thread pool implementation with support for progress monitors,
etc.
John
Martin Oberhuber wrote on 10/30/2008 04:47:02 PM:
> Hi Scott, Pawel and all,
>
> it looks like this Thread has long left the resources/EFS
> aspect of things, and moved to a more general discussion
> about infrastructure for asynchronous coding patterns.
>
> I'd thus like to make the discussion more general. We
> seem to agree that there needs to be some base infrastructure
> for asynchronous coding patterns, and (perhaps even more
> important) API Documentation for how to properly use that
> infrastructure. If this base infrastructure is unified,
> we all win.
>
> Thanks Scott for volunteering to offer your expertise
> as well as contributions. What could be the next steps
> towards making it happen? I'm assuming that the base
> infrastructure should be in Equinox. Is anyone from
> the Equinox team listening and could guide through
> their process for contribution?
>
> Assuming that Equinox is right, we should perhaps first
> find a proper place for this discussion; then argue
> about good infrastructure/patterns; these need to be
> backed by some actual usage somewhere. Right now, it
> looks like what we'll want is at least
>
> Future (aka RequestMonitor, AsyncExecutionResult)
> Callback (aka Listener)
> Status/MultiStatus (async variant)
> Executor/Queue/Realm (for posting async Runnables/Callbacks
> in a well-known Thread)
>
> along with some well-documented Exception types (cancellation,
> timeout) as well as Threading paradigm.
>
> How to proceed from here? Potential clients of async
> certainly include DD/DSF and ECF, perhaps Resources/EFS;
> who else is interested in infrastructure for async?
>
> Cheers,
> --
> Martin Oberhuber, Senior Member of Technical Staff, Wind River
> Target Management Project Lead, DSDP PMC Member
> http://www.eclipse.org/dsdp/tm
>
>
>
> > -----Original Message-----
> > From: eclipse-incubator-e4-dev-bounces@xxxxxxxxxxx
> > [mailto:eclipse-incubator-e4-dev-bounces@xxxxxxxxxxx] On
> > Behalf Of Scott Lewis
> > Sent: Wednesday, October 29, 2008 7:06 PM
> > To: E4 developer list
> > Subject: Re: [eclipse-incubator-e4-dev] [resources] EFS, ECF
> > and asynchronous
> >
> > Hi Martin,
> >
> > Oberhuber, Martin wrote:
> > > Hi Scott,
> > >
> > > to me, Futures and Listeners don't need to be a contradiction.
> > >
> >
> > Before my further comments...I don't believe they are in
> > conflict either
> > (that is, both can be used in some cases as described by Martin). I
> > guess I sort of presented them as exclusive, but I didn't
> > really mean to
> > have it be so.
> >
> > > What's more interesting to me, is how to deal with Progress.
> > > When a Progress Monitor already exists for the client, then
> > > using it makes a lot of sense even if the result is obtained
> > > asynchronously:
> > >
> > > final CBFuture<IFileStore[]> childrenF =
> > myFileStore.list(myProgress);
> > > childrenF.chain(new Callback() {
> > > public void onDone(IStatus result) {
> > > if (result.isOK()) {
> > > handleResult(childrenF.get());
> > > }
> > > };
> > > });
> > >
> > > I'm using class "CBFuture" as an "enhanced Future" that allows
> > > registering Callbacks. Using a Callback style of handling things,
> > > or CBFuture.waitFor() remains up to the client. Note that I'm
> > > using a "chain()" method to indicate that the Framework/Future could
> > > allow chaining multiple callbacks such that one is exeucuted after
> > > the other. Also note how the callback retrieves the result of
> > > computation from the Future, and not from the callback itself.
> > >
> >
> > I agree that the general issue of how to handle progress monitors is
> > tricky. Although I accept your ideas above as a possible
> > solution, I'm
> > not sure whether this is the 'right' mechanism or not for 'remote
> > progress monitoring'. I've been thinking about this for some
> > time, but
> > still don't feel like I have a good general solution for supporting
> > IProgressMonitor for remote procedures.
> >
> > > The problems that I have seen with callbacks in our products
> > > in the past are listed on
> > >
> > http://wiki.eclipse.org/E4/Pervasive_Themes#Becoming_More_Asynchronous
> > >
> > > * Much boilerplate code - Closures would be nice to avoid explosion
> > > of anonymous inner classes, which could cause bloat
> > >
> > > * Need clarification on what thread and in what context the
> > > callback will be called
> > >
> > > * When debugging, it is very hard to trace back the flow of
> > > operation across multiple callback invocations. It can even
> > > make debuging close to impossible unless some Tracing
> > > functionality for the callbacks is built into the Framework
> > > (we ended up doing this in our commercial product).
> > >
> > > * Exception handling needs to be clarified. Java6 Future only
> > > provides Future#isCanceled(), that's not enough since the
> > > result of an operation might also be an exception. I'm
> > > introducint "Istatus result" above but that's also not
> > > optimal.
> > >
> >
> > I agree these are other issues...thanks.
> >
> >
> > > The synchronous variant needs more verbosity writing it than
> > > one would expect, because cancellation and errors (exceptions)
> > > need to be handled, wrapped and potentially re-wrapped with
> > > Futures:
> > >
> > > final CBFuture<IFileStore[]> childrenF =
> > myFileStore.list(myProgress);
> > > try {
> > > handleResult(childrenF.get());
> > > } catch(CancellationException e) {
> > > throw new OperationCancelledException(e);
> > > } catch(ExecutionExeption e) {
> > > throw new CoreException(new Status(/*.blabla*/));
> > > }
> > >
> > > although that could perhaps be simplified if we declared some
> > > Eclipse specific implementation of Future which throws the
> > > kinds of Exceptions that we already know (like CoreException
> > > embedding an Istatus) instead of the JRE's ExecutionException
> > > that's really alien to our current code.
> > >
> >
> > Yes, I agree that these are issues. I also agree that it would be
> > useful to have Equinox-specific impls of Future (which is really what
> > the IAsyncResult interface was meant to be and can/will
> > change to be if
> > desired). Further, I've recently also realized that there
> > also should
> > probably be something like remote impls of
> > IStatus/MultiStatus, as I've
> > been doing some remote mgmt interfaces (i.e. accessing and managing a
> > remote processes' OSGi framework, p2, etc)...and it's clear
> > to me that
> > it is going to be very helpful to support the usage of
> > IStatus/Multistatus as return values, as well as exceptions in remote
> > service access. I agree that Future/IAsyncResult as well as
> > IStatus/Multistatus and exception types should be widely
> > available (i.e.
> > in Equinox rather than redone/available in many locations above
> > Equinox). We (ECF) are willing to contribute (and modify as desired)
> > what we've done in this area (e.g. IAsyncResult+impl,
> > RemoteStatus/RemoteMultiStatus, exception types) as desired.
> >
> > Scott
> >
> >
> >
> > > Cheers,
> > > --
> > > Martin Oberhuber, Senior Member of Technical Staff, Wind River
> > > Target Management Project Lead, DSDP PMC Member
> > > http://www.eclipse.org/dsdp/tm
> > > _______________________________________________
> > > eclipse-incubator-e4-dev mailing list
> > > eclipse-incubator-e4-dev@xxxxxxxxxxx
> > > https://dev.eclipse.org/mailman/listinfo/eclipse-incubator-e4-dev
> > >
> >
> > _______________________________________________
> > eclipse-incubator-e4-dev mailing list
> > eclipse-incubator-e4-dev@xxxxxxxxxxx
> > https://dev.eclipse.org/mailman/listinfo/eclipse-incubator-e4-dev
> >
> _______________________________________________
> eclipse-incubator-e4-dev mailing list
> eclipse-incubator-e4-dev@xxxxxxxxxxx
> https://dev.eclipse.org/mailman/listinfo/eclipse-incubator-e4-dev
_______________________________________________
eclipse-incubator-e4-dev mailing list
eclipse-incubator-e4-dev@xxxxxxxxxxx
https://dev.eclipse.org/mailman/listinfo/eclipse-incubator-e4-dev
