Re: [SQLObject] select() causes SQLObject + webware application to die

[Ian B. <ia...@co...>]

Scott Russell wrote:
> ### Start 2 ##
> class TestPage(Page):
>     def writeContent(self):
>         peeps = Person.select(Person.q.email=='xxx')
>         self.writeln('''Welcome.''')
> ### End 2 ##

Note that this doesn't do anything.  When you call .select(), it only 
creates a query, it doesn't run it or send anything to the database. 
Only when you iterate or get an index will a query happen.

> Once again, this holds up wonderfully.  It never fails, as far as I can
> tell.  Rock solid.
> 
> Now, for the bad one.  One more TestPage servlet, this time with an
> accessor for peeps.
> 
> ### Start 3 ##
> class TestPage(Page):
>     def writeContent(self):
>         peeps = Person.select(Person.q.email=='xxx')
>         p = peeps[0]
>         self.writeln('''Welcome''')
> ### End 3 ##

Now you've actually done something.  Which means there's two concurrent 
threads hitting the same site.

I've written badly unthreadsafe MySQL code before, and it gives me wonky 
results but not a crash like you describe.  That's ugly.  But I assume 
it's some sort of threadsafety issue.

Have you tried turning debugging on in the connection (add debug=1 to 
your connection constructor)?  Whatever comes before the fall?  Each 
line starts with a connection ID, which should be useful.  Adding the 
thread name to DBConnection.printDebug would also probably be useful, like:

     def printDebug(self, conn, s, name, type='query'):
         if type == 'query':
             sep = ': '
         else:
             sep = '->'
             s = repr(s)
         n = self._connectionNumbers[id(conn)]
         spaces = ' '*(8-len(name))
         threadName = threading.currentThread().getName()
         print ('%(n)2i:%(threadName)s/%(name)s%(spaces)s%(sep)s %(s)s' %
                locals())

   Ian