Re: Maintenance state

Hi all,

Wari Wahab <[email protected]> writes:
> Another pyblosxom user who has been in the background but doing some
> funny exploratory stuff is IWS, I don't even know his name, and can't
> really read his website. You can look up his pyblosxom page @
> http://iws.dyndns.org/blog/net/pyblosxom

This page is my masquerade place. My real name is deleted from the pages.
So please call me IWS.

> The second is the stability part. This, for me is 2.x stuff, so it's in
> the back burner. Pyblosxom is not stable when runnning as a long
> process, that is, when running as a webware servlet, or as mod_python
> program. This is due to a few factors:
>
>   * CGI program was in mind when designing pyblosxom
>   * Global variables everywhere especially in tools.py
>   * File locking needs fixing, when one instance of pyblosxom is
> touching something, the other should just wait.
>   * Contention issues, globals in one state, when another instance wants
> another state, etc.

My pages don't reflect very recent results. I like to put them here.

After/during developing new features of pyblosxom(MySQL interface, recent
comment list, read more plug-in, and so on), I reach the same conclusion:

- if we run pyblosxom as CGI processes, there is a possibility to do
destructive operations simultaneously by the two process. It will cause
strange errors in entryshelve (see:
	http://iws.dyndns.org/blog/net/pyblosxom/entryshelve-error.html
It contains Japanese characters, but you can understand the contents.)
So we need flock or something to prevent it.

- if we run pyblosxom as thread in a process by mod_python, there is a
possibility to do destructive operations simultaneously by the two threads.
So we need semaphore or reference counter or something to prevent it.

Anyway we need a concurrency control in pyblosxom.

I thought providing reference counter for global variables in tools.py is
easy and interesting than using flock for CGI pyblosxom.  So I implemented
it three weeks ago. In this approach, each instance of Pyblosxom calls two
functions: tools.ref_registry() and tools.close_registry() to update a
reference counter. The global variables are re-initialized and the cache is
closed, only if the counter = 0 or after a long idle period. Otherwise,
multiple Pyblosxom instances share variables peacefully.

It seemed work well. In fact, during over three weeks observation of
pyblosxom + entryMySQL + mod_python, I have never got any error! More stable
than pyblosxom as CGI with entryshelve. The problem seems be solved. I can
declare it, ....... maybe :-). 

> For this, a rewrite might be needed, in order to achieve such a robust
> piece of code, while having the ability to run as a CGI process as well.

I don't claim my code is robust, smart or worth to merge to the code. This
is a result of experimental programming. But I hope this is a help. Please
check my code, guru:

http://iws.dyndns.org/src/pyblsxom/tools.diff
        (In this patch, I introduced a new storage variable for misc. cache.)
http://iws.dyndns.org/src/pyblsxom/pyblosxom.diff

Lastly, I'd like to add two more topics:

1. new cache method: cache/entryMySQL.py

http://iws.dyndns.org/src/pyblsxom/entryMySQL.py

As described above, I developed an interface to MySQL for a cache storage.
It works well for three weeks. Since it still lacks a code for the database
initialization: you must make a database and a table by hand, its version is
0.9. But it might become 1.0 in future without modification.
Note: its performance has not examined yet.

2. comments.py can generate recent comment list

http://iws.dyndns.org/src/pyblsxom/comments.py
http://iws.dyndns.org/src/pyblsxom/comments.py.diff

You can display a list of the most recent comments for jumping to the
entries quickly. Since this feature depends to comments.py strongly, I
decided not to make as a separate plug-in but an extension of the original
comment.py. Please read the comment at the head of the source.

sincerely,
-- 
IWS-VG7A+C9aekxy/[email protected]
 



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