[wildfly-dev] Ordered child resources

[Kabir Khan]

> On 1 Apr 2015, at 19:48, Brian Stansberry <brian.stansberry at redhat.com> wrote:
> 
> Are the classes in your 2) and 3) new base classes, or examples of what 
> users would need to do?
> 
> Given your question, I figure it's the latter.
Yes they are examples cut and paste from a test case I am working on.
> 
> It seems like it would be fairly straightforward to add the 3) stuff to 
> AbstractAddStepHandler via a simple constructor param. The 1) stuff is 
> pretty simple too, but doing both it and 3) starts to get messy in terms 
> of too many constructor variants.
Rather than polluting the existing class too much, since this should really be an uncommon case (?) perhaps we need an AbstractOrderedAddStepHandler. But it is a bit weird since the parent and the child both need to override this differently. It shouldn’t be too hard to come up with something nicer though, I’ll let you know once I have had a play.
> 
> What about re-ordering? Done via add/remove?
Yes that would need to be done via remove and add (with add-index). Moving stuff around would still need to trigger awareness that something changed, but perhaps that could be done with a handler registered for these parent resources. e.g. something along the lines of /some=where:reorder-children(child-type=orderedA, order=[tree, bush, hedge]). For now I see this as a nice to have enhancement which can happen in the future :-)
> 
> On 4/1/15 7:54 AM, Kabir Khan wrote:
>> I am working on being able to order child resources, this is important for things like jgroups where the protocol order matters. On top of the domain operations work I inherited from Emanuel the order will get propagated through the domain. Currently for jgroups the only way to adjust the protocol order is to remove all protocols and add them again, and on the domain ops branch (before what I am outlining here) upon reconnect any new protocols end up at the end of the slave’s list.
>> 
>> The steps to make a child resource ordered are currently:
>> 1) Make the ‘parent’ resource’s add handler call a different factory method:
>> 	@Override
>> 	protected Resource createResource(OperationContext context) {
>> 		Resource resource = Resource.Factory.create(false, “orderedA”, “orderedB"); //Names of the child types where ordering matters
>> 		context.addResource(PathAddress.EMPTY_ADDRESS, resource);
>> 		return resource;
>> 	}
>> 
>> 2) In the ordered child resource definitions, override the new getOrderedChildResource() operation to
>> 	class OrderedChildResourceDefinition extends SimpleResourceDefinition {
>> 		public OrderedChildResourceDefinition(PathElement element) {
>> 			super(PathElement.pathElement(“orderedA", new NonResolvingResourceDescriptionResolver(),
>> 				new OrderedChildAddHandler(REQUEST_ATTRIBUTES), new ModelOnlyRemoveStepHandler());
>> 		}
>> 
>> 		@Override
>> 		protected boolean getOrderedChildResource() {
>> 			return true;
>> 		}
>> 		….
>>   }
>> This has the effect of adding a parameter called ‘add-index’ to the ‘add’ operation’s description. So if you have
>> 	/some=where/orderedA=tree
>> 	/some=where/orderedA=bush
>> You can do e.g. /some=where/orderedA=hedge:add(add-index=1) and end up with:
>> 	/some=where/orderedA=tree
>> 	/some=where/orderedA=hedge
>> 	/some=where/orderedA=bush
>> 
>> 3) The final part is to adjust the ordered child resource’s add handler to honour the add-index parameter:
>> 
>> 	class OrderedChildAddHandler extends AbstractAddStepHandler {
>> 		public OrderedChildAddHandler(AttributeDefinition... attributes) {
>> 			super(attributes);
>> 	}
>> 
>> 	@Override
>> 	protected Resource createResource(OperationContext context, ModelNode operation) {
>> 		if (!operation.hasDefined(ADD_INDEX) || operation.get(ADD_INDEX).asInt() < 0) {
>> 			return super.createResource(context);
>> 		}
>>           	return context.createResource(PathAddress.EMPTY_ADDRESS, operation.get(ADD_INDEX).asInt());
>> 	}
>> 
>> 4) Not really related to what a user needs to do to create an ordered resource, but 1-3 are made possible by that on the resource interface I have two new methods:
>>   /**
>>    * Return the child types for which the order matters.
>>    *
>>    * @return {@code true} if the order of the children matters. If there are no ordered
>>    * children and empty set is returned. This method should never return {@code null}
>>    */
>>   Set<String> getOrderedChildTypes();
>> 
>>   /**
>>    * Register a child resource
>>    *
>>    * @param address the address
>>    * @param index the index at which to add the resource. Existing children with this index and higher will be shifted one uo
>>    * @param resource the resource
>>    * @throws IllegalStateException for a duplicate entry or if the resource does not support ordered children
>>    */
>>   void registerChild(PathElement address, int index, Resource resource);
>> 
>> 
>> The main question I have is whether 1-3 are too ‘fragile’ and if we need something to enforce/glue this together a bit more? At the same time ordered child resources should be the exception rather than the rule.
>> 
>> 
>> 
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>> 
> 
> 
> -- 
> Brian Stansberry
> Senior Principal Software Engineer
> JBoss by Red Hat
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