multiprocessing on freebsd

[Tim Arnold]

On Mar 17, 11:26 am, Philip Semanchuk <phi... at semanchuk.com> wrote:
> On Mar 17, 2010, at 9:30 AM, Tim Arnold wrote:
>
>
>
>
>
> > Hi,
> > I'm checking to see if multiprocessing works on freebsd for any
> > version of python. My server is about to get upgraded from 6.3 to 8.0
> > and I'd sure like to be able to use multiprocessing.
>
> > I think the minimal test would be:
> > ---------------------
> > import multiprocessing
> > q = multiprocessing.Queue()
> > ---------------------
>
> > with 6.3, I get
>
> > File "/usr/local/lib/python2.6/multiprocessing/__init__.py", line
> > 212, in Queue
> >    from multiprocessing.queues import Queue
> >  File "/usr/local/lib/python2.6/multiprocessing/queues.py", line 22,
> > in <module>
> >    from multiprocessing.synchronize import Lock, BoundedSemaphore,
> > Semaphore, Condition
> >  File "/usr/local/lib/python2.6/multiprocessing/synchronize.py", line
> > 33, in <module>
> >    " function, see issue 3770.")
> > ImportError: This platform lacks a functioning sem_open
> > implementation, therefore, the required synchronization primitives
> > needed will not function, see issue 3770.
>
> Hi Tim,
> Under FreeBSD 8/Python 2.6.2 I get the same result, unfortunately.  
> That's a pity because sem_open works under FreeBSD >= 7.2 as we  
> discussed before.
>
> Issue 3770 is closed with the note, "we've removed hard-coded platform  
> variables for a better autoconf approach." I'm using the Python built  
> from FreeBSD's ports, and the note makes me think that it's possible  
> that if I built my own Python from the Python.org tarball rather than  
> ports the problem would go away due to autoconf magic. I don't have  
> the time to offer to do this for you, unfortunately. But why not  
> install FreeBSD 8 under VirtualBox or somesuch and give it a go  
> yourself?
>
> A couple of quirks I noted related to FreeBSD & POSIX IPC that you  
> might find useful --
> - The sem and mqueuefs kernel modules must be loaded, otherwise you'll  
> get a message like this when you try to create a semaphore or message  
> queue:
> Bad system call: 12 (core dumped)
>
> Under 8.0 they're loaded by default, I think.
>
> - C apps that want to use message queues must link to the realtime  
> libs (pass -lrt to the linker). This tripped me up for a while.  
> Linking to the realtime libs is required for all POSIX IPC calls under  
> Linux; FreeBSD does not require it for semaphores or shared mem, only  
> message queues.
>
> Hope this helps
> Philip

Hi Philip,
Thanks for that information (esp the linker info). Once the machine is
upgraded, I'll try building python from the tarball. I'll post back
here with the results.

here's hoping!
thanks,
--Tim