[infinispan-dev] Defining new commands in modules

[Galder Zamarreño]

Looks nice and clean. As a SPI developer, it might be interesting to understand better the difference between visitable and nonvisitable commands and when to use which?

This kind of info could be embedded in the javadoc of http://goo.gl/OkvU4 or http://goo.gl/isR00 respectively? Or do you plan to write a wiki at some point?

On Mar 5, 2011, at 3:32 AM, Manik Surtani wrote:

> I know it's been a while since we spoke about this, but I now have a (working) prototype of this work.
> 
> Changes to Infinispan core to accommodate this:
> 
> 	https://github.com/maniksurtani/infinispan/commit/a6085647f2ac908d9307c9cd6866ed412bc12406
> 
> Sample module making use of custom commands (both visitable and not) as well as custom interceptors:
> 
> 	https://github.com/infinispan/infinispan-sample-module
> 
> Enjoy!
> Manik
> 
> On 29 Sep 2010, at 21:06, Manik Surtani wrote:
> 
>> So this is an extension to the discussion around a GenericCommand that has been going around.  IMO a GenericCommand is a big -1 from me for various reasons - the whole purpose of the command pattern is so we have strongly typed and unit testable commands.  This will help the ongoing work by Mircea, Sanne and Israel on various modules that need to define custom commands.
>> 
>> I proposed the following solution to Mircea earlier today, I'll repeat here for you guys to discuss.  Note that this is a *half baked* solution and needs more thought!  :-)
>> 
>> * If a module needs to define custom commands, it should define its own ReplicableCommand implementations in its' own module.
>> * It should define a sub-interface to Visitor (MyModuleVisitor) with additional methods to handle the new commands
>> * Interceptors defined in this module should extend CommandInterceptor AND implement MyModuleVisitor
>> * These new commands can be created directly, or via a new CommandFactory specially for these commands.
>> 
>> Now for the un-finished bits.  :)
>> 
>> * How does RemoteCommandFactory instantiate these new commands?  The module should have a way of registering additional command IDs with RemoteCommandFactory.fromStream().  See 
>> 
>> http://fisheye.jboss.org/browse/Infinispan/branches/4.2.x/core/src/main/java/org/infinispan/commands/RemoteCommandsFactory.java?r=2327#l59
>> 
>> Perhaps RemoteCommandFactory.fromStream() should look up the ID in a map of command creator instances, and each module can register more of these with the RemoteCommandFactory?
>> 
>> * How do interceptors defined in the core module handle commands it isn't aware of?  handleDefault()?  Or should we define a new handleUnknown() method in Visitor for this case, which would default to a no-op in AbstractVisitor?  E.g., in a module-specific command such as MyModuleCommand, I would implement:
>> 
>> class MyModuleCommand implements ReplicableCommand {
>> 
>> public Object acceptVisitor(InvocationContext ctx, Visitor visitor) throws Throwable {
>>   if (Visitor instanceof MyModuleVisitor) {
>>         return ((MyModuleVisitor) visitor).visitMyModuleCommand(ctx, this);
>>   } else {
>>         return visitor.handleUnknown(ctx, this);
>>   }
>> }
>> 
>> }
>> 
>> Cheers
>> Manik
>> 
>> PS: There is no JIRA for this.  If we like this approach and it works, I suggest we create a JIRA and implement it for 4.2.  The impl should be simple once we resolve the outstanding bits.
>> --
>> Manik Surtani
>> manik at jboss.org
>> Lead, Infinispan
>> Lead, JBoss Cache
>> http://www.infinispan.org
>> http://www.jbosscache.org
>> 
>> 
>> 
>> 
>> 
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> 
> --
> Manik Surtani
> manik at jboss.org
> twitter.com/maniksurtani
> 
> Lead, Infinispan
> http://www.infinispan.org
> 
> 
> 
> 
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--
Galder Zamarreño
Sr. Software Engineer
Infinispan, JBoss Cache