Re: onError from image request inbox lost
Ian Bell <i.bell@...>
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None of the enterprise bridges implement this functionality and the timeout is always relied upon to invoke the error call-back.
That said I did look into this at one stage for a similar scenario but we ended up going with an alternate solution.
Some of the things that cropped up during that investigation and need thought about here as well
1) Threading - Subscription requests are sent from the default thread, whereas the subscription call-backs (ie onError) happen off the subscription thread.
2) Subscription clean-up - Effects of this slightly different scenario need to considered in terms of its impact on the subscription state-machine.
3) Race conditions - There are already a few race conditions around the sending of multiple requests and replies happening at the same time as the timeout especially when the queue is backed up, again new scenarios might make this a more frequent occurance.
4) Imagerequest destruction - The cleanup of the objects needs to be handled carefully and I'm not convinced its completely correct as it is.
Also it feels like there is a sort of overlap with this and the publisher events discussion as in this a msg being sent and an error being returned.
From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of Tom Doust
Sent: 25 March 2015 08:46
To: Sam Wilson; email@example.com
Subject: Re: [Openmama-dev] onError from image request inbox lost
I have been looking at a similar issue with snapshot subscriptions on our TREP bridge. The problem is a bit more general in that it includes conditions such as handling a bad symbol name but nevertheless the problem is how to notify on a callback.
I don't have any answers at the moment as I haven't been able to allocate any time to it but I had kind of assumed that there should be a way of calling the mamaSubscription OnError callback.
It would be interesting to know what mama client applications expect to happen and also what does the wmw bridge do in this situation
From: firstname.lastname@example.org [mailto:email@example.com] On Behalf Of Sam Wilson
Sent: 23 March 2015 17:42
Subject: [Openmama-dev] onError from image request inbox lost
I've got a (hopefully) quick question for you guys.
First off, our scenario: instead of getting initials and recaps from an interactive publisher, our middleware bridge allows market data subscribers to get initials/recaps from a cache. The cache can report a condition where there is no data for a particular subject, and we'd like to give that information to applications. Currently our bridge does nothing in this case, and eventually the image request times out.
Now my question: I'm attempting to deliver an onError from the inbox of an image request in a market data subscription to the application, but the image request does not provide an onError callback to the subscription. (See http://tinyurl.com/ld8cwfh) Is this intentional, or would it make sense to pass the onError callback through? If passing the onError through is correct, what is the right way to handle the destroy handle?
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