David,
So iterators are bad? :-P
Cheers,
Ed
David Orme wrote:
Re: explosions of inner classes
On Android (and probably other embedded VMs) construction is expensive
and also leads to more GC pauses. Google recommends minimising
architectures that force a lot of short-lived objects.
Just one more data point for the discussion.
-Dave Orme
On Oct 29, 2008 5:30 AM, "Oberhuber, Martin"
<[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
Hi Scott,
to me, Futures and Listeners don't need to be a contradiction.
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.
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.
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.
Cheers, -- Martin Oberhuber, Senior Member of Technical Staff,
Wind River Target Management Project...
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