[Python-Dev] Issue #10348: concurrent.futures doesn't work on BSD

[Philip Semanchuk]

On Dec 29, 2010, at 5:46 PM, Nick Coghlan wrote:

> On Thu, Dec 30, 2010 at 8:33 AM, Antoine Pitrou <solipsis at pitrou.net> wrote:
>> On Wed, 29 Dec 2010 23:24:32 +0100
>> "Martin v. Löwis" <martin at v.loewis.de> wrote:
>>>> I don't have a good suggestion (or a computer with a keyboard
>>>> anywhere near me) right now, but making a migration/fallback to SYSV
>>>> style semaphores a release blocker seems like a mistake to me.
>>> 
>>> And indeed, I don't propose to make that a release blocker. Instead,
>>> I propose to disable support for the module (either multiprocessing
>>> or concurrent.futures only) on FreeBSD, and make such disabling a
>>> release blocker.
>> 
>> I don't really agree with this. There's no need to explicitly forbid
>> use of multiprocessing from FreeBSD. First, it is not our task to
>> validate that each and every OS conforms to the APIs it claims to
>> implement. Second, such disabling would make life uselessly more
>> complicated for users the day FreeBSD actually fixes their stuff.
> 
> Also, I believe you can get it to work on FreeBSD 7.2 by fiddling with
> the arbitrary limits. So +1 for skipping the affected tests on FreeBSD
> so the buildbot state can tell us something useful (conditionally
> wrapping them with "expected failure" may be even better, as then
> we'll find out when the FreeBSD out-of-the-box configuration actually
> supports running them).

A bit of info about FreeBSD 7.2 and 8.0 (the only versions I have installed). My installs are set up explicitly for testing and so they have had very little customization.

- `sysctl -a|grep p1003` displays the config values specific to POSIX IPC. I think `sysctl -a|grep ipc` shows values for SysV IPC. It looks like the POSIX 1003_1b names in sysctl are similar to the names here (e.g. SEM_NSEMS_MAX, SEM_VALUE_MAX, etc.) --
http://pubs.opengroup.org/onlinepubs/009695399/basedefs/limits.h.html

- Under my 7.2, sysctl.p1003_1b.sem_nsems_max == 0 and I can't create semaphores with my posix_ipc extension. After `kldload sem`, sysctl.p1003_1b.sem_nsems_max == 30 and my posix_ipc semaphore & shared mem demo works.

- Under my 8.0, sysctl.p1003_1b.sem_nsems_max == 30 and my posix_ipc semaphore & shared mem demo works even without `kldload sem`. `kldstat` doesn't show sem.ko as loaded, so I assume that POSIX semaphores are now a default part of the kernel.

- Under my 7.2 *and* 8.0, sysctl.p1003_1b.mq_open_max == 0 and I can't create a message queue with my posix_ipc extension. After `kldload mqueuefs`, sysctl.p1003_1b.mq_open_max remains 0 (huh?) but my posix_ipc message queue demo works.

- Under my 8.0, sysctl.p1003_1b.sem_nsems_max is read only even if I change it in /etc/sysctl.conf. According to this post, sem_nsems_max doesn't become dynamic until 8.1:
http://www.gossamer-threads.com/lists/python/dev/875319?do=post_view_threaded


Hope this helps a bit
Philip