Example code for server and client threads communication using DistributedObjects.

The code is based on Apple article (http://developer.apple.com/documentation/Cocoa/Conceptual/Multithreading/articles/CocoaDOComm.html) and DistributedObjectsForInterThreadCommsCrash.

Notes:

• The DO voodoo is hidden in Server class, the client need only one method for setting the server
• Does not leak mach ports like Apple example code

Issues:

• It would be nice to hide the DO voodoo completely and create the worker thread with [Server server]
• It would be nice to create the server thread synchronically, blocking until it is created.

//// Server.h

/*

Creating a server thread

Client call [Server connectionToServerThreadForClient:self] to create a server thread and get back a connection to the thread. When the thread is ready, it will call the client setServer: method. After the client set the server, it can communicate with the server over DO.

Destroying a server thread

Client call [server terminate], then release the server as usual.

*/

@protocol Server

// Terminate the server thread

• (oneway void)terminate;

// Add other methods that servers must have

@end

@protocol Client

// Called from the server when its ready

• (void)setServer:(in id)server;

// Add other methods that clients must have

@end

@interface Server : NSObject { BOOL running; }

// Create new thread and get back a connection the thread

• (NSConnection *)connectionToServerThreadForClient:(id )client

// Private method used only by the Server class to connect to a new created thread

• (void)connectWithPorts:(NSArray *)portArray;

• (BOOL)isRunning;

@end

//// Server.m

@implementation Server

• (NSConnection *)connectionToServerThreadForClient:(id )client { NSPort *port1 = [NSPort port]; NSPort *port2 = [NSPort port];

  NSConnection *connection = [NSConnection connectionWithReceivePort:port1 sendPort:port2]; [connection setRootObject:client];

  // Ports switched here NSArray *portArray = [NSArray arrayWithObjects:port2, port1, nil];

  [NSThread detachNewThreadSelector:@selector(connectWithPorts:) toTarget:[self class] withObject:portArray]; return connection; }

• (void)connectWithPorts:(NSArray *)portArray { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; Server *instance = self alloc] init];

  [[NSConnection *connection = [[NSConnection alloc] initWithReceivePort:[portArray objectAtIndex:0] sendPort:[portArray objectAtIndex:1]]; [connection setRootObject:instance];

  // Connect with the client [(id )[connection rootProxy] setServer:instance];

  // Run until termination do { [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]]; } while ([instance isRunning]);

  // If not invalidated, the ports leak and instance is never released connection receivePort] invalidate]; [[connection sendPort] invalidate];

  [connection release]; [instance release]; [pool release]; }

• (void)terminate { running = NO; }

• (BOOL)isRunning { return running; }

@end

//// Client.h

#import Server.h // for Client protocol

@interface Client : [[NSObject { id server; NSConnection *serverConnection; } @end

//// Client.m

@implementation Client

• (void)setServer:(id)anObject { [anObject retain]; [anObject setProtocolForProxy:@protocol(Server)]; [server release]; server = (id )anObject;

  // You may start to communicate with the server now }

@end

–NirSoffer