[jboss-as7-dev] EJB Remote client design

Okay so after a bunch of discussion with various personages, it looks like we have some remote EJB client design shaken out. Please read through a couple times to make sure you have gotten a clear understanding to avoid questions that are already answered here. Client API ---------- We'll introduce a concept of an "EJB invocation receiver" or "EJB receiver" for short. The job of this fellow is to receive invocations on behalf of a connection to a peer or a cluster or locally. So for the Remoting transport, there is a 1:1 correspondence between connections and EJB receivers. Multiple EJB receivers can be collected up into a single "EJB client context", each with a "preference" level. Same-VM receivers will typically have a higher preference than remote receivers. An EJB remote proxy (and by extension, its Handle) identify their EJB by the combination of application name, module name, "distinct" name, and bean name. All of the equals()-type operations that are specified by EJB are implemented in terms of this basic level of equivalence (though some types have additional criteria, like SFSB using session ID as well). There is no notion of a specific server address or URI in a proxy or handle. The "distinct" name is an _optional_ name which can be associated with a deployment (by deployment descriptor, and possibly also by configuration) in the event that two different deployments which are visible from one client have the same application and module name. (Yes, I know you can't have two deployments with the same app+module name in one server; however, a client can "see" more than one server at once and may need to distinguish, especially if the user does not control the name of the deployment.) Each EJB receiver has an obligation to keep the EJB client context updated with the list of module identities that it can access. When a proxy is invoked upon, the EJB client context uses this table to select the destination. This means that for the Remoting protocol for example, the server sends back messages informing the client of changes in deployment status (which should be relatively infrequent) as well as sending an initial summary of what modules are available. Most client interceptors are associated with both an EJB client context and a receiver type. This is because things like transactions, security, etc. will vary in their implementation based upon the protocol in use. We _may_ support protocol-independent interceptors, however we'll have to evaluate use cases first. If we do then most likely they'd work with a protocol-dependent counterpart; for example, a general security interceptor might attach additional principal information to the invocation in a standard spot, which the protocol-specific interceptor might then publish to the server (or not). An invocation on a remote proxy will use whatever EJB client context is current for the calling thread. Thus remote proxies and handles can be passed from one context to another (directly or via cloning or serialization) without any special action being taken. If no EJB client context is available, remote invocation will fail immediately. Remote Async Invocation ----------------------- Any Session Bean remote interface method which returns a Future will always be treated as asynchronous by the client. Methods which return void but are visibly (to the client) marked with the appropriate annotation will be treated as asynchronous. Other methods which return void will not be automatically treated as asynchronous, though the server protocol allows for a message to come back to inform the client that the invocation will proceed asynchronously. If the client knows that a method is asynchronous or wants to call a void method asynchronously, it may use a static API method to acquire an asynchronous "view" of that interface so that all calls to void methods proceed asynchronously: myProxy.theVoidMethod(); // called sync unless the server unblocks EJB.async(myProxy).theVoidMethod(); // called async always This cannot be solved any other way as the client might not have access to the EJB metadata which specifies whether the method is asynchronous. Client JNDI ----------- Client JNDI is just a simple in-memory JNDI implementation. We will not automatically bind anything to it at all, except in two possible cases: 1. A simple configuration file which describes what to bind, or 2. A configuration instructing a binding list to be fetched from somewhere. Clients running in an AS7 instance or in an AS7 application client container will be using our server JNDI implementation which supports injection, not the client JNDI implementation, which is reserved for truly standalone clients. Server Implementation --------------------- The EE subsystem already contains most of the required APIs for handling remote invocations. Any remotely accessible ComponentView will be registered with the remote invocation service along with its app/module/distinctName identification. A special in-VM EJB receiver will also exist and will be similarly updated with the current available component views and their modules. Management configurations will be introduced for the purpose of establishing and maintaining Remoting connections to remote servers. EJB client contexts should be created for each deployment, and a deployment descriptor should be made available to any EE deployment for the purpose of associating Remoting connections (and probably clusters etc.) with the EJB client context for that EE module. This allows each deployment to specify what remote servers it can "see", while still keeping the network configuration business in the central management model. All deployments on the server which have an EE client context will have the in-VM receiver added to it automatically, so that it can access all EJBs in the server via remote interface locally. Summary ------- Okay I think that's it for the first draft. Please give feedback on anything that I might have missed or anything that's just outright wrong and needs to be changed. In particular I'm currently assuming that IIOP exists in a world outside of other invocation forms, but that might not actually be desirable. -- - DML