[wildfly-dev] CLI batches in control flow blocks

[Brian Stansberry]

On 9/4/15 12:55 AM, Alexey Loubyansky wrote:
> On 09/04/2015 12:10 AM, Brian Stansberry wrote:
>> The risk is this can break existing scripts, which we've sought to
>> avoid. A couple breakage scenarios:
>>
>> 1) Step 1 needs to happen in a batch with Step 2; now it won't so the
>> script breaks.
>> 2) Step 1 works but for some reason Step 2 fails, and now Step 1 isn't
>> rolled back.
>>
>> The first one is more likely, but the second one is a bigger concern, as
>> the user may not be aware Step 1 wasn't rolled back.
>>
>> Do you have any sense of how common either of those scenarios would be?
>
> Unfortunately, no. I don't get much feedback on this except for created
> issues that I referenced.
> I wouldn't bring it up unless this wasn't a major version release, of
> course.
>

Yes, it's now or not for a long time.

>> Below are bad ideas that I wrote down and then thought better of, but
>> I'll send them in case it sparks a thought.
>>
>> I. Since there is already logic for dropping out of the batch for things
>> like cd, ls, could it be modified as follows?
>>
>> a) Close any current batch and execute that batch.
>> b) Execute the cd, ls, etc
>> c) Proceed, and if the next statement isn't a cd, ls etc, start a new batch.
>>
>> That seems like a better semantic for cd and ls anyway.
>
> I don't think so. The batch mode is also a composition/editing mode. cd
> and ls are useful when writing commands/operations that should be added
> to the batch. Imagine editing a batch and wishing to cd before entering
> next lines. That won't be possible without explicit holback-batch, cd
> and then batch again. That would be inconvenient.
>

Thanks; that's a very good point. Yesterday, I was having a hard time 
seeing the point of ls inside an if/else; now I get it. :)

>> With that, reload and shutdown can be treated the same as cd, ls.
>
> For reload and shutdown that does seem to make sense. So, a possible
> alternative is making them exceptions.
>

I said yesterday (below) that this was a bad idea because it can still 
break scripts or prevent rollback, same as your proposal. But I think in 
practice this wouldn't be a real drawback, since AIUI the bugs mean any 
existing script with reload/shutdown in the middle of a bunch of other 
ops would be broken anyway. Right?

>> Why a bad idea? Doing it as I suggest has the same two drawbacks as
>> requiring the user to declare the batch. :( Just perhaps less likely to
>> occur.
>>
>> II. Is an --auto-batch=true|false param to if/else/try/catch/finally
>> possible? Why a bad idea? To solve the breakage problem it would need to
>> be 'true' by default, thus forcing users forever to declare that they
>> want the non-broken mode, *plus* they have to declare the batches.
>
> As a param to if/else/try/catch/finally this doesn't make sense to me.
> Because then the user could simply explicitly start bodies with batch.
> This kind of argument could make sense as a launching script argument
> for the whole cli session, imo.
>

The drawbacks are the same though. To avoid breaking old scripts the 
default behavior would have to be the old behavior, and then the people 
wanting the new, correct behavior would have to jump through strange hoops.

> Thanks,
> Alexey
>
>>
>>
>> On 9/3/15 10:42 AM, Alexey Loubyansky wrote:
>>> Hello everyone,
>>>
>>> I've been thinking about changing how the bodies of if-else and
>>> try-catch-finally are treated by the CLI.
>>>
>>> Up until now every control flow block (i.e. between if and else, between
>>> else and end-if, etc) was executed as a batch. So, when a block was
>>> selected for the execution, the CLI would enter the batch mode and
>>> proceed adding operations (and commands translated to operations) to it.
>>> If a command can't be translated to an operation, it would be executed
>>> outside the batch immediately (that's done for commands like cd, ls,
>>> etc). After the last line of the body processed, the batch (if not
>>> empty) is executed.
>>>
>>> But this doesn't work when mixing operations with shutdown or reload
>>> commands (they do translate to operations but they have additional logic
>>> related to re-connecting). shutdown/reload will be executed outside the
>>> batch and before the batch is complete.
>>>
>>> Currently open issues for this
>>> https://issues.jboss.org/browse/WFCORE-876
>>> https://issues.jboss.org/browse/WFCORE-533
>>>
>>> So, I think it was a mistake to execute the bodies of control flow
>>> blocks as batches. It would be better leave them as usual sequences of
>>> command lines and if the user wants a batch, he/she could add batch
>>> command explicitly.
>>>
>>> I wanted to ask for opinions. Could we make this change in WildFly 10?
>>>
>>> Thanks,
>>> Alexey
>>> _______________________________________________
>>> wildfly-dev mailing list
>>> wildfly-dev at lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/wildfly-dev
>>>
>>
>>
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-- 
Brian Stansberry
Senior Principal Software Engineer
JBoss by Red Hat