Interrupting a blocking function frolm another thread.

[superhac007 at gmail.com]

On Apr 8, 8:09 pm, Adam Skutt <ask... at gmail.com> wrote:
> On Apr 8, 5:52 pm, superhac... at gmail.com wrote:
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> > On Sunday, April 8, 2012 3:55:41 PM UTC-5, Adam Skutt wrote:
> > > On Apr 8, 2:45 pm, "superhac... at gmail.com" <superhac... at gmail.com>
> > > wrote:
> > > > I am using the python module nfqueue-bindings which is a nfqueue
> > > > packet intercepting module.  It uses the following snippet of code to
> > > > start the process:
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> > > > print "trying to run"
> > > > try:
> > > >      q.try_run()
> > > >      except KeyboardInterrupt, e:
> > > >      print "interrupted"
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> > > > The q.try_run() method blocks.   I would like to be able to interrupt
> > > > this the same way you can hit control-c to unblock it, but from
> > > > another thread.  Does anyone have any idea on how to do this?  Is
> > > > there some sort of Exception I can generate from another thread that
> > > > would do this?
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> > > The simplest and most reliable way will be to modify the asynchronous
> > > I/O example athttps://www.wzdftpd.net/redmine/projects/nfqueue-bindings/repository/...
> > > to do what you want.  The classical way to accomplish this would be to
> > > create a second I/O descriptor (via os.pipe or similiar) and wait for
> > > that descriptor in the same async I/O loop.  When you want to stop the
> > > loop, send a message (could be a single byte) to the second descriptor
> > > and then respond appropriately in your asynchronous I/O handler.
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> > > However, simply ignoring the nfqueue socket while doing other
> > > processing might be acceptable too.  I would read the documentation
> > > and ask questions carefully before taking that approach, as it may
> > > lead to lost data or other problems.  The viability of this approach
> > > depends heavily on your application.
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> > > Adam
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> > Thanks for the reply Adam.  I am still confused with the example with the example you linked to.  I have only been working with Python for a couple of weeks, but I am fluent with C.  Given the example you linked to, are you saying that this is the run loop for asynchronous comm that a end user of the module could use?  Or is this something with the nfqueue-bindings module that I would I have to modify.  I don't recognize the the main loop in the example.
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> asyncore is a standard python module for handling asynchronous I/O
> operations (i.e., select/poll operations).  The main loop in that
> example is handled by the 'asyncore.loop()' call, which just calls
> select() in a loop until all channels are closed.  You're looking at
> the standard Python library technique for an asynchronous I/O event
> loop.
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> asyncore.file_dispatcher enables use of asyncore.loop() with standard
> UNIX FDs.  nfqueue.queue objects provide access to their underlying
> FDs so you can wait on them.  asyncore.loop() is the main loop of the
> application, performing endless select/poll waits and calling
> 'handle_read' whenever the netfilter FD has data for reading.  You can
> find more details about the module in the Python library docs.
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> Since your code is Linux specific, you can always call os.select() or
> os.poll() if it makes you feel better, but I don't think that's going
> to simplify anything here.
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> Hopefully that helps you.
>
> Adam

Thanks for the through explanation.  I now know what I need to do.


Thanks again!