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Re: [ecf-dev] Async-Methods

Hi Wim and Eugen,

On 11/22/2010 1:28 PM, Wim Jongman wrote:
Hi Eugen,

It is funny that this pops up frequently lately. I guess it would be sweet if we could implement some kind of ProgressMonitor while executing the task much like the progress monitor in Eclipse. 

In the mean time, you can implement your own progress service OR use the ECF Future feature. You call a method async and you get a Future back. You can poll the Future while you show an "indefinite" progress (the one that sweeps) based on the status of the Future.

Wim is quite right...this is a way to do progress monitoring on consumer side of a remote service.   Admittedly it isn't ideal, the client's progress indication doesn't actually get data from the host/service side in order to show progress....rather it just assumes some progress has been made because time passes.

By way of explanation...the real problem here is that normal/OSGi remote method call doesn't support callbacks (and that's what IProgressMonitor or custom equivalent is).  The reason for this is that it doesn't generally support remote method parameter pass-by-reference...which is needed to trivially support callbacks.  With most providers remote method parameters are necessarily passed by value (i.e. method parameters are serialized and a copy is sent to the remote service host...rather than a distributed object reference).  

However, it's quite possible to define/create a messaging pattern to implement progress monitoring...e.g. with the ECF shared object API and/or the datashare API.  This isn't strictly OSGi remote services, though.  Both ECF APIs can/could be pretty easily used to define the messaging to support remote progress monitoring.  One of the things that I've contemplated doing is to add such a feature to RegistrySharedObject (via the shared object api)...and perhaps even to the remote services API...for example exposing it via a new type of IFuture that would allow the specification of client-side progress monitors that actually use server-side messages to update.  But, I haven't been able to personally work on this thread yet given the attention of OSGi remote services.  If folks would like to persue adding such a feature then please open an enhancement request and consider contributing or supporting work in that area.


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