[jboss-dev-forums] [Design of JBossCache] - Re: static field replication in PojoCache

[bela@jboss.com]

"ben.wang at jboss.com" wrote : 
  | 
  | I introduced that field annotation (@Replicatable) becuase I reckon there may be a case I don't want to replicate 1) any of the POJO static variables at all (this is happening most often); or 2) all of my static variables, e.g.,
  | 
  | 
  |   | org.jboss.cache.pojo.annotation.PojoCacheable
  |   | public class POJO
  |   | {
  |   |    @org.jboss.cache.pojo.annotation.Replicatble
  |   |    public static int someStaticVar;
  |   |    
  |   |    public static int anotherStaticVar; // this one won't get replicated.
  |   |   ...
  |   | }
  |   | 
  | 
  | 


I think this is not intuitive: @PojoCacheable replicates *all* variables, so static vars should be included.
You can exclude static vars using the transient keyword or @transient annotation.

anonymous wrote : 
  | anonymous wrote : #2 Of course we need to support another static variable ! Ideally we adhere to the Java semantics
  | 
  | Sure, it will be supported. I meant in my originally post that we won't support a static variable of "aspectized" POJO type, e.g.,
  | 
  |   | org.jboss.cache.pojo.annotation.PojoCacheable
  |   | public class Foo
  |   | {
  |   | ...
  |   | }
  |   | 
  |   | org.jboss.cache.pojo.annotation.PojoCacheable
  |   | public class POJO
  |   | {
  |   |    @org.jboss.cache.pojo.annotation.Replicatble
  |   |    public static Foo someStaticVar; // we cant support that someStaticVar is of type Foo of which is PojoCacheable.
  |   |   ...
  |   | }
  |   | 
  | 
  | Reason? Well, static variable is usually initialized failry early in the program lifecycle. So support of another POJO type to be managed by the PojoCache can be troublesome. I imagine mostly the static type to be primitive. Or am I assuming too much?
  | 

Can we at least try before we give up ? :-) I don't (currently) see why static vars should only be of primitive types... So, okay, we can create those instances but only replicate them once we have been fully initialized.

anonymous wrote : 
  | anonymous wrote : #5 Why ? we can have N someStaticVars per *cluster*...
  | 
  | Now I don't get you. If someStaticVars is replicated, then there can only be a someStaticVar per *cluster* (sure, different VM will have their own instances). I was proposing to allow inside each VM, only one PojoCache instance is allowed to have static variable replication. Elias' discussion is also focused on this area as well.
  | 

Why should only 1 PojoCache be allowed to have static var replication inside the same VM ? This sounds like an arbitrary restriction...

anonymous wrote : 
  | Finally, on the naming of @PojoCacheable instead of @Clustered or @Replicated. I have thought about that before. I think @Clustered or @Clusterable is not appropriate becuase we are talking about state replication only (i.e., no client side load balancing).
  | 
  | As for @Replicated, it is possible. But the expectation will be different. E.g., a user should not expect that once the Pojo is annotated and instantiated, then thing will happen automatically. That is, we are not using the API-less model; we still need to have api to *attach* the POJO. So @Replicated tag is a bit overloaded, IMO.
  | 

Still much better than @PojoCacheable, which is horrible

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