Re: NSMachPort thread safety

FROM : Adam R. Maxwell
DATE : Sun Mar 02 05:52:04 2008

On Mar 1, 2008, at 8:35 PM, Kyle Sluder wrote:

> On Sat, Mar 1, 2008 at 9:01 PM, Adam R. Maxwell <<email_removed>> 
> wrote:

>> Thanks, but I think you're misinterpreting the example :).  The 
>> object
>> has a single NSMachPort ivar, added to the some thread's runloop.
>> When a notification arrives on a different thread in
>> processNotification:, it messages the NSMachPort.  When the port's
>> delegate receives handleMachMessage: it processes the notification
>> since it's guaranteed to be on the correct thread.

>
> Okay, so I don't understand where the problem is.  The reason for the
> locking and thread-checking is so that two threads can share the
> non-thread-safe NSPort object.  Unless when I said "messages" you were
> thinking in Mach port terms; I meant you can't send an Objective-C
> message from thread A to a non-thread-safe object on thread B (unless,
> of course, you implement the locking yourself).


Yes, and there's no lock around the call to sendBeforeDate:.  Hence my 
question: is the example flawed, or is NSMachPort thread safe?  To 
make things more interesting, NSMachPort appears to be implemented on 
top of CFMachPort, which is thread safe according to the docs...but 
the NS layer sometimes removes thread safety (as in NSRunLoop vs. 
CFRunLoop).  I reimplemented one class with a CFRunLoopSource and a 
raw mach port, but using NSMachPort is easier.

--
adam