On Jan 13, 2009, at 6:41 PM, Mel wrote:
Philip Semanchuk wrote:
I'm working on message queue support, but the Sys V IPC API is a
headache and takes longer to code against than the POSIX API.
I hadn't found it that bad. I have a C extension I should perhaps
clean up
and make public.
Have you compared the SysV objects to the POSIX objects? I'll give you
two examples of how SysV is more trouble with which to work.
Example 1 ---
The SysV objects expose a ton of information that show up as Python
attributes. For instance, a sysv_ipc.Semaphore object has 16
attributes: key, id, value, undo, block, mode, uid, gid, cuid, cgid,
last_pid, waiting_for_nonzero, waiting_for_zero and o_time. The first
two and last eight are read-only, the middle six are read-write.
Contrast this to a posix_ipc.Semaphore object which has two read-only
attributes: name and value.
All of those attributes on the SysV object add up to a lot of code.
Furthermore, the SysV attributes have types of key_t, mode_t, uid_t,
gid_t, pid_t, time_t, etc. I've spent the past few days researching
these types and trying to find out whether they're signed or unsigned,
guaranteed to fit in a long, etc. I also need to know what Python
types are appropriate for representing these. For instance, anything
that can exceed a C long can also exceed a Python int, and so I need
to return a Python long object if the C value exceeds LONG_MAX.
When I returned to the sysv_ipc code a few days ago, my intention was
to add message queue support to it, but instead I've gotten distracted
chasing type-related bugs that won't show up until e.g. someone
compiles the module on a 64-bit platform and tries to use a key that
exceeds 0xFFFFFFFF, or compiles it on some weird 16-bit embedded
processor that exposes another of my flawed type assumptions. The
POSIX API is so much simpler that I spend much less time working on
type-related drudgery.
Example 2 ---
SysV shared memory has to be attached and detached and accessed with
the un-Pythonic read & write methods. I'd like to support buffer-type
access (like slicing), but that's more code to be written. And there's
another 16 attributes to expose.
POSIX shared memory OTOH is mmapped, and there's already a Python
library for that. For posix_ipc.SharedMemory objects I had to write a
constructor, an unlink() method, and code for three read-only
attributes and I was done. Nice.
I invite you to look at my extension and compare:
http://semanchuk.com/philip/sysv_ipc/
Maybe your code can benefit from what I've done, or vice versa.
Good luck
Philip
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