threading support in python

[Lawrence Oluyede]

Re: threading support in python

Sandra-24 <sandravandale@ yahoo.comwrote:

Oh I'm aware of that, but it's not what I'm looking for. Mod_mono just
lets you run ASP.NET on Apache. I'd much rather use Python :) Now if
there was a way to run IronPython on Apache I'd be interested.

Take a look here:

http://lists.ironpython.com/pipermail/users-ironpython.com/2006-March/00

2049.html
and this thread:

http://www.mail-archive.com/users@lists.ironpython.com/msg01826.html

--
Lawrence - http://www.oluyede.org/blog
"Nothing is more dangerous than an idea
if it's the only one you have" - E. A. Chartier

[Lawrence Oluyede]

Re: threading support in python

Lawrence Oluyede <rhymes@myself. comwrote:

Take a look here:

http://lists.ironpython.com/pipermail/users-ironpython.com/2006-March/00

2049.html
and this thread:
http://www.mail-archive.com/users@li.../msg01826.html

Also this: http://www.codeproject.com/useritems/ipaspnet.asp

Google is you friend! :-)

--
Lawrence - http://www.oluyede.org/blog
"Nothing is more dangerous than an idea
if it's the only one you have" - E. A. Chartier

[skip@pobox.com]

Re: threading support in python


AndreThis seems to be an important issue and fit for discussion in the
Andrecontext of Py3k. What is Guido's opinion?

Dunno. I've never tried channeling Guido before. You'd have to ask him.
Well, maybe Tim Peters will know. He channels Guido on a fairly regular
basis.

Skip

[Sandra-24]

Re: threading support in python

sjdevnull@yahoo .com wrote:

You can do the same on Windows if you use CreateProcessEx to create the
new processes and pass a NULL SectionHandle. I don't think this helps
in your case, but I was correcting your impression that "you'd have to
physically double the computer's memory for a dual core, or quadruple
it for a quadcore". That's just not even near true.

Sorry, my bad. What I meant to say is that for my application I would
have to increase the memory linearly with the number of cores. I have
about 100mb of memory that could be shared between processes, but
everything else would really need to be duplicated.

As I said, Apache used to run on Windows with multiple processes; using
a version that supports that is one option. There are good reasons not
to do that, though, so you could be stuck with threads.

I'm not sure it has done that since the 1.3 releases. mod_python will
work for that, but involves going way back in it's release history as
well. I really don't feel comfortable with that, and I don't doubt I'd
give up a lot of things I'd miss.

Having memory protection is superior to not having it--OS designers
spent years implementing it, why would you toss out a fair chunk of it?
Being explicit about what you're sharing is generally better than not.

Actually, I agree. If shared memory will prove easier, then why not use
it, if the application lends itself to that.

But as I said, threads are a better solution if you're sharing the vast
majority of your memory and have complex data structures to share.
When you're starting a new project, really think about whether they're
worth the considerable tradeoffs, though, and consider the merits of a
multiprocess solution.

There are merits, the GIL being one of those. I believe I can fairly
easily rework things into a multi-process environment by duplicating
memory. Over time I can make the memory usage more efficient by sharing
some data structures out, but that may not even be necessary. The
biggest problem is learning my way around Linux servers. I don't think
I'll choose that option initially, but I may work on it as a project in
the future. It's about time I got more familiar with Linux anyway.

It's almost certainly not worth rewriting a large established
codebase.

Lazy me is in perfect agreement.

I disagree with this, though. The benefits of deterministic GC are
huge and I'd like to see ref-counting semantics as part of the language
definition. That's a debate I just had in another thread, though, and
don't want to repeat.

I just took it for granted that a GC like Java and .NET use is better.
I'll dig up that thread and have a look at it.

I didn't say that. It can be a big hit or it can be unnoticeable. It
depends on your application. You have to benchmark to know for sure.
>
But if you're trying to make a guess: if you're doing a lot of heavy
lifting in native modules then the GIL may be released during those
calls, and you might get good multithreading performance. If you're
doing lots of I/O requests the GIL is generally released during those
and things will be fine. If you're doing lots of heavy crunching in
Python, the GIL is probably held and can be a big performance issue.

I don't do a lot of work in native modules, other than the standard
library things I use, which doesn't count as heavy lifting. However I
do a fair amount of database calls, and either the GIL is released by
MySQLdb, or I'll contribute a patch so that it is. At any rate, I will
measure, and I suspect the GIL will not be an issue.

-Sandra

[Paul Rubin]

Re: threading support in python

skip@pobox.com writes:

It was removed at one point in the dim, dark past (circa Python 1.4) on an
experimental basis. Aside from the huge amount of work, it resulted in
significantly lower performance for single-threaded apps (that is, the
common case).

That's probably because they had to put locking and unlocking around
every access to a reference count. A real GC might have fixed that.

[Paul Rubin]

Re: threading support in python

"sjdevnull@yaho o.com" <sjdevnull@yaho o.comwrites:

I think it's even worse. The standard Python library offers
shared memory, but not cross-process locks.

>
File locks are supported by the standard library (at least on Unix,
I've not tried on Windows). They work cross-process and are a normal
method of interprocess locking even in C code.

I may be missing your point but I didn't realize you could use file
locks to synchronize shared memory in any useful way. File locks are
usually made and released when the file is opened and closed, or at
best through flock or fcntl calls. Shared memory locks should
generally be done with mechanisms like futex, that in the no-wait case
should not involve any system calls.

[sjdevnull@yahoo.com]

Re: threading support in python

Paul Rubin wrote:

"sjdevnull@yaho o.com" <sjdevnull@yaho o.comwrites:

I think it's even worse. The standard Python library offers
shared memory, but not cross-process locks.

File locks are supported by the standard library (at least on Unix,
I've not tried on Windows). They work cross-process and are a normal
method of interprocess locking even in C code.

>
I may be missing your point but I didn't realize you could use file
locks to synchronize shared memory in any useful way.

You can, absolutely. If you're sharing memory through mmap it's
usually the preferred solution; fcntl locks ranges of an open file, so
you lock exactly the portions of the mmap that you're using at a given
time.

It's not an unusual use at all, Unix programs have used file locks in
this manner for upwards of a decade--things like the Apache public
runtime use fcntl or flock for interprocess mutexes, and they're quite
efficient. (The futexes you mentioned are a very recent Linux
innovation).

[Paul Rubin]

Re: threading support in python

"sjdevnull@yaho o.com" <sjdevnull@yaho o.comwrites:

You can, absolutely. If you're sharing memory through mmap it's
usually the preferred solution; fcntl locks ranges of an open file, so
you lock exactly the portions of the mmap that you're using at a given
time.

How can it do that without having to touch the PTE for every single
page in the range, which might be gigabytes? For that matter, how can
it do that on regions smaller than a page? And how does another
process query whether a region is locked, without taking a kernel trap
if it's locked? This sounds absolutely horrendous compared to a
futex, which should usually be just one or two user-mode instructions
and no context switches.

It's not an unusual use at all, Unix programs have used file locks in
this manner for upwards of a decade--things like the Apache public
runtime use fcntl or flock for interprocess mutexes, and they're quite
efficient. (The futexes you mentioned are a very recent Linux
innovation).

Apache doesn't use shared memory in the same way that something like a
database does, so maybe it can more easily tolerate the overhead of
fcntl. Futex is just a somewhat standardized way to do what
programmers have done less portably since the dawn of multiprocessors .

[mystilleef]

Re: threading support in python

You can use multiple processes to simulate threads via an IPC
mechanism. I use D-Bus to achieve this.

http://www.freedesktop.org/wiki/Software/dbus

km wrote:

Hi all,
Are there any alternate ways of attaining true threading in python ?
if GIL doesnt go then does it mean that python is useless for
computation intensive scientific applications which are in need of
parallelization in threading context ?
>
regards,
KM
---------------------------------------------------------------------------
On 4 Sep 2006 07:58:00 -0700, bayerj <bayerj@in.tum. dewrote:

Hi,

GIL won't go. You might want to read
http://blog.ianbicking.org/gil-of-doom.html .

Regards,
-Justin

--

http://mail.python.org/mailman/listinfo/python-list

[Bryan Olson]

Re: threading support in python

sjdevnull@yahoo .com wrote:

Bryan Olson wrote:

>I think it's even worse. The standard Python library offers
>shared memory, but not cross-process locks.

>
File locks are supported by the standard library (at least on Unix,
I've not tried on Windows). They work cross-process and are a normal
method of interprocess locking even in C code.

Ah, O.K. Like Paul, I was unaware how Unix file worked with
mmap.


--
--Bryan

[Bryan Olson]

Re: threading support in python

I wrote:

Ah, O.K. Like Paul, I was unaware how Unix file worked with
mmap.

Insert "locking" after "file".


--
--Bryan

[lcaamano]

Re: threading support in python

Here's a relevant post

http://mail.python.org/pipermail/python-3000/2006-April/001051.html

or

http://tinyurl.com/fod9u


skip@pobox.com wrote:

AndreThis seems to be an important issue and fit for discussion in the
Andrecontext of Py3k. What is Guido's opinion?
>
Dunno. I've never tried channeling Guido before. You'd have to ask him.
Well, maybe Tim Peters will know. He channels Guido on a fairly regular
basis.
>
Skip

--
lpc