[Haskell-cafe] Re: Re: Waiting for thread to finish

[Paul Moore]

On 28/11/2007, Ben Franksen <ben.franksen at online.de> wrote:
> It was fun, too. For instance, the OP's question reminded me of a little
> generic wrapper I wrote  -- more or less for my own amusement -- during the
> course of this project. It outputs dots during an operation that might take
> a little longer to finish (a database query in my case)... just so the user
> doesn't get nervous ;-) And because I enjoyed it so much (and to show off)
> I threw in the timing measurement...
[...]
> I think nobody in his right mind would even try to do something like that in
> C or Perl or whatever, at least not if it wasn't strictly a requirement and
> correct operation is important (the script gets executed as part of our
> build process and a subtle concurrency bug could lead to a wrong
> configuration for the target control system). In Haskell it was so easy to
> do that I just couldn't resist.

That's a neat idea. Just (a) because I like the idea, and (b) because
I'm contrary :-) I coded up the equivalent in Python. It also looks
beautifully clean:

from __future__ import with_statement

import threading
import sys

# Implementation of Ticker class
class Ticker(threading.Thread):
    def __init__(self, msg):
	threading.Thread.__init__(self)
	self.msg = msg
	self.event = threading.Event()
    def __enter__(self):
	self.start()
    def __exit__(self, ex_type, ex_value, ex_traceback):
	self.event.set()
	self.join()
    def run(self):
	sys.stdout.write(self.msg)
	while not self.event.isSet():
	    sys.stdout.write(".")
	    sys.stdout.flush()
	    self.event.wait(1)

# Here's how we use it...
if __name__ == '__main__':
    import time
    with Ticker("A test"):
	time.sleep(10)
    with Ticker("Second test"):
	time.sleep(5)
	raise Exception("Bang!")

Paul.