I believe that I now have solved my problem using a launchd "on-demand" daemon with Distributed Objects (DO).

I was only using TCP ports here for initial development because some of the launchd "on-demand" sample code does and because I had been unable to create an NSMachPort with the mach_port_t value I received from launchd. However, while writing a response to a replay to my message (which I had originally posted on the Cocoa-dev list), I caught a trivial programming error that fixed my NSMachPort creation problem (they were coming back nil) and also allowed DO to work with the launchd daemon "on-demand." I have not yet tried the UNIX domain socket approach to client<->daemon communication DO yet, and since I believe that Mach ports are preferred for DO I do not intend to at this point.

Here is the mach services version of my code (which works with the launchd daemon "on-demand"):

// TestDaemonLaunchd.plist

<dict>

<key>ServiceIPC</key>

<true/>

<key>MachServices</key>

<dict>

<key>com.example.TestDaemon</key>

</true>

</dict>

<key>OnDemand</key>

<true/>

<key>Label</key>

<string>com.example.TestDaemon</string>

<key>ProgramArguments</key>

<array>

<string>/path/to/TestDaemon</string>

</array>

</dict>

// TestDaemon.m

int main (int argc, const char * argv[]) {

NSAutoreleasePool *pool = [NSAutoreleasePool new];

// NOTE: Getting the Mach port descriptor (mp) from launchd.

launch_data_t checkinRequest = launch_data_new_string(LAUNCH_KEY_CHECKIN);

launch_data_t checkinResponse = launch_msg(checkinRequest);

launch_data_t machServicesDict = launch_data_dict_lookup(checkinResponse, LAUNCH_JOBKEY_MACHSERVICES);

launch_data_t machPort = launch_data_dict_lookup(machServicesDict, "com.example.TestDaemon");

mach_port_t mp = launch_data_get_machport(machPort);

launch_data_free(checkinResponse);

launch_data_free(checkinRequest);

NSMachPort *receivePort = [[NSMachPort alloc] initWithMachPort:mp];

NSConnection *connection = [NSConnection connectionWithReceivePort:receivePort sendPort:nil];

[receivePort release];

id testObject = [NSObject new];

[connection setRootObject:testObject];

[[NSRunLoop currentRunLoop] run];

[testObject release];

[pool release];

return 0;

}

// TestClient.m

int main (int argc, const char * argv[]) {

NSAutoreleasePool *pool = [NSAutoreleasePool new];

NSConnection *connection = [NSConnection connectionWithRegisteredName:@"com. example.TestDaemon" host:nil];

[connection setRequestTimeout:10.0];

[connection setReplyTimeout:10.0];

// NOTE: No NSPortTimeoutException is raised when used with an "on-demand" launchd daemon after switching to Mach ports for DO communication.

id proxy = [connection rootProxy];

[pool release];

return 0;

}