Is there a way of producing a deferred graph in a Python program at a given point in time?  Perhaps something based on graphviz and objgraph.py?  We're able to detect when we're having the problem, we just don't (yet) know its cause.

I'm looking at some code with a bit over 200 addCallback/addErrback/addCallbacks in it.

It's got a problem where sometimes the deferreds seem to just stop executing.  I see in the doc it says that this can happen if you've neglected to add an errback to the end of one or more of your deferred chains.

One of the people who's been here longer than me, indicated that he's gone through the code looking for such issues, and didn't find any.  This suggests to me that either there's some other cause, or that it really is a deferred without a final errback, but it's hidden in a dark corner of the code somewhere.