As requested in the RFC (section 0.3) and the OSGi design git hub repo README (https://github.com/osgi/design#feedback), please provide any comments on an RFC in the form of a bug at https://www.osgi.org/bugzilla/enter_bug.cgi?product=OSGi%20Specification.
Thanks, -- BJ Hargrave Senior Technical Staff Member, IBM OSGi Fellow and CTO of the OSGi Alliance hargr...@us.ibm.com office: +1 386 848 1781 mobile: +1 386 848 3788 From: Mike Wilson <mike...@hotmail.com> To: "'OSGi Developer Mail List'" <osgi-dev@mail.osgi.org> Date: 2014/03/13 18:35 Subject: [osgi-dev] comments on async rfc: async call semantics Sent by: osgi-dev-boun...@mail.osgi.org So, here's the first write-up in my promised feedback on the Async RFC 206 (from March 03) at: https://github.com/osgi/design/tree/master/rfcs/rfc0206 >From section 5.4 we learn how to start an asynchronous invocation that has a return value: List asyncList = asyncService.mediate(listRef); Promise<Boolean> promise = asyncService.call(asyncList.contains("badEntry")); and one that has no return value (void method): mediator.clear(); Promise<Boolean> promise = asyncService.call(); By extending the reasoning I'm guessing that the following is also valid: boolean tmp = asyncList.contains("badEntry"); Promise<Boolean> promise = asyncService.call(tmp); The text explains that the actual asynchronous invocation doesn't take place until calling Async.call(), ie: asyncList.contain("badEntry"); // prepare async call asyncService.call(...); // sends async call I'm surprised by this division of labour between the proxied methods and Async.call. Intuitively, I would expect the call to the proxied method to actually start the asynchronous invocation. Thus, according to the RFC if I just write: asyncList.contain("badEntry"); there will be no invocation at all. I think something like the following model would be more intuitive, and probably more fail-safe as well: - let the proxied method start the asynchronous invocation - let the call to asyncService just deal with retrieving the promise, via asyncService.promise(...) - don't leave any state hanging outside calls to the Async service or proxied methods (ie the "prepared" data) Examples: Asynchronous invocations where I don't care about the promise or return value: asyncList.contain("badEntry"); // sends async call asyncList.clear(); // sends async call Call with return value that I want to follow via promise: Promise<Boolean> promise = asyncService.promise(asyncList.contains("badEntry")); ^ retrieves ^ sends async call promise Call without return value that I want to follow via promise: Promise<Boolean> promise = asyncService.promise( new Runnable() { public void run() { asyncList.clear(); } } ); which has the cost of being a bit verbose but avoids the problem with dangling state. It also sugars much nicer with Java 8 lambdas: Promise<Boolean> promise = asyncService.promise(() -> asyncList.clear()); or method references (if there are no parameters): Promise<Boolean> promise = asyncService.promise(asyncList::clear); I hope I haven't misunderstood the RFC text too much and that you will find these suggestions interesting. Best regards Mike _______________________________________________ OSGi Developer Mail List osgi-dev@mail.osgi.org https://mail.osgi.org/mailman/listinfo/osgi-dev
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