[Python-Dev] release candidate rules and timeit API question
Tue, 1 Jul 2003 08:19:23 -0500
Skip> import time
Skip> class Timeout(Exception): pass
Skip> def await_condition(predicate, timeout):
Skip> delay = 0.0005
Skip> endtime = time.time() + timeout
Skip> while True:
Skip> if predicate():
Skip> remaining = endtime - time.time()
Skip> if remaining <= 0: # time's up, predicate always failed
Skip> raise Timeout
Skip> delay = min(delay * 2, remaining, .05)
Skip> time.sleep(delay) # reduce CPU usage by using a sleep
Guido> I wonder if the right refactoring wouldn't be to add an acquire
Guido> with timeout method to the built-in lock type?
In my case I use await_condition() to gracefully empty a Queue of database
connection objects at termination time.
conn = self.conn_pool.get(block=0)
return len(self._leftovers) == self.poolsize
def empty_conn_pool(self, poolname, maxwait):
self._leftovers = 
print "could only find", len(self._leftovers),
print "connections for", poolname
It's a bit clunky, but I wouldn't be able to use an acquire() with a
timeout directly. I'd need a Queue.get with a timeout as well.
Besides, wouldn't there be places where this progressive backoff would be
useful in non-threaded contexts?