thread safe SMTP module

[Gordon Messmer]

Aahz wrote:
> 
> That doesn't make any sense.  Blocking I/O generally releases the GIL,
> which is the whole reason Python doesn't totally suck for threading.

Nevertheless, among the caveats listed at 
http://docs.python.org/lib/module-thread.html is:

"Not all built-in functions that may block waiting for I/O allow other 
threads to run. (The most popular ones (time.sleep(), file.read(), 
select.select()) work as expected.)"

> There may be other thread problems, but I doubt that you have correctly
> analyzed their source.

I subclassed smtplib.SMTP and replaced only the lines of code that had 
to do with blocking IO (connect, send and receive operations). 
Beforehand, python would occasionally lock up. Having made those 
changes, python stopped locking up.  I think the problem was pretty well 
apparent.  I can't pin it down to which one of those three operations 
was at fault, and it may be that only one was.  However, when I use 
non-blocking IO, the application works.  When I used smtplib.SMTP, it 
didn't.

I'm open to other explanations.