Oleg,
That's a rant, it's off topic, and I'm probably posting on the wrong forum,
but anyway.
I feel your pain, I've spent a good few hours this week debugging threaded
programs. At one point I found that I was using the same telnet instance on
two threads at the same time. No wonder things were messed up. But it took
me two hours to find the root of the problem.
But the fact is that today you have to deal with parallelism in one form or
another. It can be threads or multiple processes, it's unavoidable. And it
will get worse with newer CPUs.
Your argument reminds me of a recent post by Guido van Rossum. If I remember
it right it was one of the posts regarding Python 3k, someone asked if there
were any plans to remove the GIL. Guido said that the someone wrote a patch
to remove the GIL. It was very complex and the performance was poor, because
of the number of extra checks. In the end it became impossible to keep the
patch synchronized with the development on the main Python trunk. Given that
and given Guido's opinion regarding threads, the GIL continues to be what it
is - a single generic lock for Python instead of a more granular locking
mechanism, which would be better for multithreaded programs (at the cost of
complexity).
Also, note that Google AppEngine uses short lived processes instead of
threads. It's a different philosophy, and it permeates everything in
Google's design.
The hidden assumption is that it's better to scale an application with
multiple processes than using threads. But performance may suffer, due to
the cost of the synchronization that becomes necessary (note that locking is
needed in both cases). Libraries such as SQLObject that keep data cached in
memory are heavily affected. There's a potential performance advantage if
you use threads with SQLObject because you keep only a single copy of the
object in memory for all threads. The difference is noticeable specially for
long running processes.
Back to the original question, wich asked about a how to for SQLObjects and
threads. I believe the same question can be applied if you resort to
multiple processes. What's the best way to do it, specially for long running
applications?
On Fri, Apr 18, 2008 at 5:13 AM, Oleg Broytmann <[EMAIL PROTECTED]> wrote:
> On Thu, Apr 17, 2008 at 04:03:08PM -0700, Fred C wrote:
> > I was wandering if there is somewhere an sqlobject 101 for threading
> > environment?
>
> My personal position is: I avoid threads like a plague.
>
> Other than that extreme position - SQLObject is mostly thread-safe,
> there are people who successfully use it in multithreading TurboGears
> applications.
> There is a controversial patch, its author claims without the patch
> SQLObject hangs, and there are reports that SQLObject hangs with the
> patch.
> The patch is now in SQLObject but will be removed in the next release
> because the last bug report was the patch causes more harm then good. (See
> why I avoid threads? Threads are evil by nature: everything in programming
> is about separation of control and responsibility - methods, classes,
> functions, modules, processes - and threads violate the law by allowing
> a few processes to share the same process space and memory; that violation
> leads to deadlocks, race conditions and subtle, hard to debug bugs.)
>
> Oleg.
> --
> Oleg Broytmann http://phd.pp.ru/ [EMAIL PROTECTED]
> Programmers don't die, they just GOSUB without RETURN.
>
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--
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Consultoria em Projetos
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blog: http://pythonnotes.blogspot.com
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