The World's Simplest Distributed Objects Example

Sunday, 17 Feb 2008

With many Cocoa design patterns, getting started is the hardest part. Distributed Objects is a perfect example of this. Run these two scripts to see how simple Distributed Objects can be. It’s all Nu, so there’s no compilation necessary. Be sure to use Nu-0.3.0 or later.

First, here are the two scripts, one for a server and one for a client. The server ‘vends’ an object over a connection to the client. The client gets a proxy for that object and communicates with the server by sending messages to the proxy.

;; server.nu
(set receivePort ((NSSocketPort alloc) initWithTCPPort:8080))
(set connection (NSConnection connectionWithReceivePort:receivePort
                     sendPort:nil))

(class Server is NSObject
     (- (id) name is
        ((NSString stringWithShellCommand:"hostname") chomp))
     (- (void) print:(id) message is
        (puts (+ "Client says: " message)))
     (- (id) add:(id) x plus:(id) y is
        (+ x y))
     ;; 'oneway' keeps the caller from hanging when the server exits
     (- (oneway void) quit is
        (puts "Exiting.")
        ((NSApplication sharedApplication) terminate:0)))

(set server ((Server alloc) init))
(connection setRootObject:server)

(puts "running server")
((NSRunLoop mainRunLoop) run)

;; client.nu
(set sendPort ((NSSocketPort alloc)
               initRemoteWithTCPPort:8080
               host:"localhost"))
(set connection (NSConnection connectionWithReceivePort:nil
                     sendPort:sendPort))
(set proxy (connection rootProxy))

(puts (+ "Connected to " (proxy name)))
(proxy print:"I know your name! It is #{(proxy name)}")
(set sum (proxy add:2 plus:2))
(proxy print:"You say that 2 plus 2 is #{sum}")
(proxy quit)
(puts "Finished")

Now in the terminal run the following:

% nush server.nu
running server

The server is now waiting for client connections. Open another terminal window and run this:

% nush client.nu
Connected to Nubie.local
Finished

Back in the terminal where you ran the server, you should see this:

% nush server.nu
running server
Client says: I know your name! It is Nubie.local
Client says: You say that 2 plus 2 is 4
Exiting.
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