[infinispan-dev] Retrieval operations with the IGNORE_RETURN_VALUES flag

[Galder Zamarreño]

On Jun 10, 2013, at 12:01 PM, Adrian Nistor <anistor at redhat.com> wrote:

> Maybe we could just clarify the javadoc of IGNORE_RETURN_VALUES and say that it only applies to write operations and is ignored for everything else? Why punish the user with an exception when doing a 'get'?
> 
> We already document there's a (very common-sense) exception for conditional writes were the flag is ignored (ISPN-3141).

I wonder if anyone noticed my reply earlier...

"The flag business does need a big re-think. Not only to separate internal from external flags (we have a jira for that [1]), but also to have a way to define which flags can be passed to a particular operation, in a way that's type-safe, and without resulting in a runtime error of the likes of "X flag cannot be used with Y operation". IOW, any error on which flag can be used with what operation should ideally be caught at compilation time. I don't have specific ideas on this right now, but I think it'd be good to achieve this."

IOW, I suggest we leave it as it is. We need to re-think it anyway. So let's tackle it in 6.0 so that a get operation can never be passed IGNORE_RETURN_VALUES flag, and this being something that's caught at **compilation time**.

I'm just about to add another internal flag to Flag as a result of the JCache 0.7 upgrade…, so need to tackle ISPN-2201 to avoid causing more confusion, and alongside avoid the issues that have been highlighted WRT which operations are allowed which flags. I'm happy to do this for 6.0.

[1] https://issues.jboss.org/browse/ISPN-2201

> 
> On 06/10/2013 12:33 PM, Dan Berindei wrote:
>> 
>> 
>> 
>> On Thu, Jun 6, 2013 at 9:08 PM, Ray Tsang <saturnism at gmail.com> wrote:
>> On Jun 6, 2013, at 13:26, Mircea Markus <mmarkus at redhat.com> wrote:
>> 
>> >
>> > On 4 Jun 2013, at 13:55, Dan Berindei <dan.berindei at gmail.com> wrote:
>> >
>> >>>> CacheLoaderInterceptor and DistributionInterceptor both honour the IGNORE_RETURN_VALUES flag for get commands, but I think it would be more useful if they ignored it - just like they ignore it for conditional commands.
>> >>>>
>> >>>> That would make it possible for users to only keep a reference to a cache.getAdvancedCache().withFlags(IGNORE_RETURN_VALUES) and use it for both read and write operations.
>> >>>>
>> >>>> What do you think?
>> >>>
>> >>> If I was to take the role of a colleague of the person who's written the Infinispan code, it'd be very confused to see a cache reference created with IGNORE_RETURN_VALUES being used for a get() operation… I can see myself thinking: "Why on earth do you call get with IGNORE_RETURN_VALUES?"
>> >>
>> >> Isn't Galder's point not to allow invoking get with IGNORE_RETURN_VALUES? As both of you pointed out, Get + IGNORE_RETURN_VALUES doesn't make any sense :-)
>> >>
>> >>
>> >> You'd think conditional operations with IGNORE_RETURN_VALUES don't make sense either, yet we have a special case to handle those as if the flag wasn't present :)
>> >
>> > I guess you're referring to ISPN-3141?
>> 
>> Exactly. Does it make sense to call cache.withFlags(IGNORE_RETURN_VALUES).putIfAbsent(k, v)? What should it return?
>> 
>>  
>> > Still I think Get + IGNORE_RETURN_VALUES doesn't make any sense :-)
>> 
>> +1. It definitely threw me off...
>> 
>> 
>> Ok, maybe IGNORE_RETURN_VALUES wouldn't be the best flag name for what I had in mind... I was thinking of a scenario where the application needs to do both reads and writes, but for writes it never needs to know the previous value. In that scenario it would make sense to call something like 
>> 
>>     cache = cacheManager.getCache().getAdvancedCache().withFlags(IGNORE_RETURN_VALUES_ON_WRITES)
>> 
>> at the beginning and only ever use that reference in the application. I agree that using the existing IGNORE_RETURN_VALUES flag for that would be a bit misleading, though.
>> 
>> Should we change anything about the IGNORE_RETURN_VALUES, then? I guess it would be relatively simple to make it so that get() operations with the flag throw an exception and (optionally) put() operations always return null. Should I create an issue in JIRA for that?
>> 
>> Cheers
>> Dan
>> 
>> 
>> 
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> 
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--
Galder Zamarreño
galder at redhat.com
twitter.com/galderz

Project Lead, Escalante
http://escalante.io

Engineer, Infinispan
http://infinispan.org