Python for Bioinformatics: Distributed Objects on OS X

Thursday, January 27, 2011

Distributed Objects on OS X

I got a simple example with Distributed Objects working. This is supposed to be the standard way to communicate between processes. I tried it first with both the Server and the Client in PyObjC. Eventually I rewrote the Server in Objective-C and then it worked.

[UPDATE: Found a great working example (old, but from an Apple engineer here). ]

The output is:

> python listen.py 
<VendedObject: 0x10010cce0>
<objective-c class NSDistantObject at 0x7fff70a64868>
woof

I'm not sure what the problem was but the error I got was

[OC_PythonString initWithBytes:length:encoding:]: unrecognized selector sent to instance 0x3635130

Server:

// gcc talk.m -o test -framework Foundation
#import <Foundation/Foundation.h>

@interface VendedObject:NSObject {}
-(NSString *) speak;
@end

@implementation VendedObject

-(NSString *) speak {
    return @"woof";
    }
@end

int main(){
    NSAutoreleasePool *pool;
    pool = [[NSAutoreleasePool alloc] init];
    VendedObject *obj;
    obj = [[[VendedObject alloc ] init] autorelease];
    NSLog(@"%@", [obj description]);
    
    NSConnection *conn;
    conn = [[[NSConnection alloc] init] autorelease];
    [conn setRootObject:obj];
    BOOL result;
    result = [conn registerName:@"my_server"];
    if (!result) {
        NSLog(@"Failed to register Name");
    }
    else {
        NSLog(@"%@", [conn description]);
    }
    [[NSRunLoop mainRunLoop] run];
    [pool drain];
    return 0;
}

Run with:

> ./test
2011-01-27 12:09:39.001 test[36995:903] <VendedObject: 0x10010cce0>
2011-01-27 12:09:39.005 test[36995:903] (** NSConnection 0x100112050 receivePort <NSMachPort: 0x100112530> sendPort <NSMachPort: 0x100112530> refCount 1 **)

You'll have to kill the process when you're done. If you have tried once already in Terminal, you will need to Quit Terminal and Re-launch. Otherwise registerName: will fail.

Client:

from Foundation import *

proxy_obj = NSConnection.rootProxyForConnectionWithRegisteredName_host_(
    #"my_server", "osxserver.local")
    "my_server", None)
if not proxy_obj:
    print 'Did not get an object from the server.'
else:
    print proxy_obj.description()
    print type(proxy_obj)
    print proxy_obj.speak()

I also tried to connect to another machine on my local network, but I couldn't get that to work either. The proxy_obj was nil/None.