Will python ever have signalhandlers in threads?

[Antoon Pardon]

Op 2004-11-15, Jp Calderone schreef <exarkun at divmod.com>:
> On 15 Nov 2004 11:44:31 GMT, Antoon Pardon <apardon at forel.vub.ac.be> wrote:
>>Op 2004-11-15, Peter Hansen schreef <peter at engcorp.com>:
>> > Antoon Pardon wrote:
>> >> AFAIU the Queue module doesn't block on a full/empty queue when
>> >> a timeout is specified but goes in a loop sleeping and periodically
>> >> checking whether place/items are available. With signals that
>> >> can be sent to a thread the queue could just set an alarm and
>> >> then block as if no timeout value was set and either unblock
>> >> when place/items are available or get signalled when the timeout
>> >> period is over.
>> >
>> > I'm fairly sure that the Queue uses an internal Event
>> > (or REvent?) to signal when space or a new item is
>> > available, so I believe your description (and possibly
>> > conclusion) above is wrong.  There should be no
>> > "periodical check", as that would imply polling.  Check
>> > the source if you're interested.
>> 
>> I did check the source, I just didn't study it carefully
>> and got my understanding mostly from the comments.
>> But anyway here is the relevant part and IMO we have
>> a polling loop here.
>> 
>
>   You are correct, but why does it matter?  The Queue class works.

Does it?

I'm not so sure. If two consumers ask simultaneously for an element
from the same empty queue. One consumer simply blocking and the
other using a timeout, I think that if an element is produced within
the timeout period the chance for the element going to either consumer
should be equal. I doubr very much we have that in the current
situation.

> Why should Python be changed in a difficult and complex way to...

It doesn't change python, it changes an implementation. Sometimes
difficult and complex implementation do a better job than easier
implementations. That we already have an implementation that works
is therefore not a strong argument against an other implementation.

> make the Queue class continue to work?  If you can give other examples
> of the uses you have in mind, that might help convince people of the
> value of this change.  But be sure you give examples of things that don't already work.

Well how about the following code, it works in the main thread, but
doesn't in a normal thread according to the documentation:

  class SystemAlarm(Exception):
    pass


  def ringalarm(signum, frame):

    raise SystemAlarm


  signal.signal(signal.SIGALRM, ringalarm)


  def lock(fl):

    ''' lock a file. If the parameter is a string, first
	open it. If the lock couldn't be aquired in five
	minutes, raise an exception.
    '''

    if isinstance(fl, type('')):
      fd = os.open(fl, os.O_RDWR | os.O_CREAT , 0700)
      fl = os.fdopen(fd, 'r+')
    signal.alarm(300)
    try:
      fcntl.flock(fl, fcntl.LOCK_EX)
      signal.alarm(0)
    except SystemAlarm:
      raise IOError("Couldn't aquire lock;")
    except:
      signal.alarm(0)
      raise

-- 
Antoon Pardon