Re: [SQLObject] Thread Safety and SQLObject

[Brad B. <br...@bb...>]

On 05/22/03 16:49, Luke Opperman wrote:
> 
> > 1. Why isn't connection = conn making this Do The Right Thing? I
> > thought the semantics I've shown above would be creating a new DB
> > connection every time, and thus hopefully have the child avoid
> > interfering with the parent.
> 
> I'm going to make a wild guess, and noting that CVS is still missing certain
> fixes that were pointed out when I last posted MemoryTransaction...:
> 
> around line 683, in new(), add the following line:
>         if kw.has_key('connection'):
>             inst = cls(None, connection=kw['connection'])
> +           inst._connection = kw['connection']
>             del kw['connection']
> 
> There are related bugs in RelatedJoin.add and RelatedJoin.remove, where they
> should use the connection from inst and not self.callingClass.
> 
> > 2. Is there any way to use SQLObject safely in a threaded environment
> > like the os.fork'ing example I have above?
> 
> So long as you don't have any of the potential concurrency problems of trying
> to update the same object from separate threads etc, I think the connection
> problem above will solve it. And even in those cases, SQLObject shouldn't blow
> up, you just don't know what data you'll end up with. :)

Well, I tried your solution but it didn't fix my problem. This isn't
because there was anything wrong with your solution, but more because
I found other problems in my own code (e.g. I hadn't quite covered
passing connections to *all* of my SQLObject-based classes being hit
in the child process :/). For simplicty's sake, I'm doing this now:

	pid = os.fork()
	if not pid:
		# child process -- process the batch file whilst control
		# has been returned to the browser
		try:
			conn = PostgresConnection(
				host='localhost',
				db='foo',
				user='bar',
				passwd='baz'
			)

			MerchantAccount._connection = conn
			MerchantProxyAccount._connection = conn
			MerchantUser._connection = conn
			PurchaseTransaction._connection = conn
			try:
				batch_file.process()
			except TooManyErrors, err:
				pass
		finally:
			os._exit(0)

This also fixed another bug where the child would never return in my
Webware servlet (three cheers for os._exit()! :).

Thanks for helping me see what I was doing wrong. :)

-- 
Brad Bollenbach
BBnet.ca