Dumping the state of a deadlocked process

andre.naess at gmail.com andre.naess at gmail.com
Sat Oct 7 11:12:13 CEST 2006

MrJean1 wrote:
> Did you try using the signal module?  If not, a basic example is here
> <http://docs.python.org/lib/node546.html> which may need to be
> extended.

I looks useful. I gave it a try, and the only weakness it has is that
when my process locks, it locks so badly that it doesn't respond to
CTRL-C, or any other signal. But by sending it a SIGQUIT which causes
it to dump the current state, and then kill it, I get the dump I need.

This is actually not a multi-threaded app. It's an application which
uses a SQL DB. The problem I was having was that I had a cursor which
started a transaction, and then never finished. Then some other cursor
came along and tried to perform a delete table, and they both locked
up. The cursor isn't ending it's transaction, and the transaction
prevents the delete table from being executed. Luckily Postgresql
allows me to list current activity, otherwise I would have been
scratching my head still.

Using logging or print statements to debug this sort of things is
highly unsatisfactory. I think the way Java uses SIGQUIT is pretty
neat, are there any reasons why Python can't adopt something similar?

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