cgi concurrency approaches?

Josiah Carlson jcarlson at nospam.uci.edu
Fri Jan 23 06:46:35 CET 2004


Paul Rubin wrote:

> I'm wondering if folks here have favorite lightweight ways of dealing
> with concurrency in cgi's.  Take a simple case:
> 
> You want to write a cgi that implements a simple counter.  The first
> time it's called, it prints "1".  The next time, "2", etc.  The naive
> implementation looks something like:
> 
>    fd = open("counter.num", "rw")
>    n = int(fd.read())
>    fd.seek(0, 0)
>    fd.write("%d"% n+1)
>    print "Content-type: text/html\n\n"
>    print n
> 
> but of course there's the obvious race condition if two people hit the
> cgi at the same time.
> 
> Fancier solutions include running an transactional database in another
> process and connecting to it, setting up a daemon that remembers the
> counter value in memory and serializes access through a socket that
> the cgi opens, using a file-system specific hack like linking to
> counter file to lock it, having a timeout/retry if the counter is
> locked, with a possible hangup if a lock file gets left around by
> accident, etc.  Each is a big pain in the neck.
> 
> Anyone have some simpler approaches?

I'd just run Xitami (www.xitami.org) and connect a LRWP (Long-Running 
Web Process).  I'm not familliar with Apache, so I don't know if 
mod_python is equivalent.

  - Josiah








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