Dumping the state of a deadlocked process

MrJean1 MrJean1 at gmail.com
Sun Oct 8 08:08:26 CEST 2006

andre.naess at gmail.com wrote:
> 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.

The Ctrl-C signal SIGINT is caught by Python by default and the signal
raises a KeyboardInterrupt exception.  For any other signals, the
signal is caught
but the signal handler is not called until Python returns to the main

Therefore, if some extension -like Postgresql in this case- is busy or
hangs, nothing
will happen until Python regains control.

> 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?

I can not anwer that.

/Jean Brouwers

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