Threading and NSPort retain count question

[James Walker]

In the "Threading Programming Guide", I'm trying to understand the 
discussion of communicating between threads using run loops and 
NSMachPort objects.  (Before someone asks why I'm not looking at an 
easier way to pass messages between threads: I need to run on Tiger.) 
I'm confused about a retain count issue.

The setup code in the main thread (Listing 3-12) creates a port with 
[NSMachPort port].  This port is installed on the run loop (does the run 
loop retain the port?) and then passed to the worker thread.  The worker 
thread function (Listing 3-14, +LaunchThreadWithPort:) takes that port 
and passes it to a method sendCheckinMessage of a newly created worker 
object.  In sendCheckinMessage (Listing 3-15), the worker object retains 
the port, and uses it as a send port for a message.  Now here's the part 
that confuses me:  When control returns to Listing 3-14, the port gets 
released.  Why?  This class method didn't retain or create the port, so 
it shouldn't be releasing it, no?

--
  James W. Walker, Innoventive Software LLC
  <http://www.frameforge3d.com/>
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