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import datetime
class NeverExpires(object):
def expired(self):
return False
class Timer(object):
"""
A simple timer that will indicate when an expiration time has passed.
"""
def __init__(self, expiration):
'Create a timer that expires at `expiration` (UTC datetime)'
self.expiration = expiration
@classmethod
def after(cls, elapsed):
"""
Return a timer that will expire after `elapsed` passes.
"""
return cls(datetime.datetime.utcnow() + elapsed)
def expired(self):
return datetime.datetime.utcnow() >= self.expiration
class LockTimeout(Exception):
'An exception when a lock could not be acquired before a timeout period'
class LockChecker(object):
"""
Keep track of the time and detect if a timeout has expired
"""
def __init__(self, session_id, timeout):
self.session_id = session_id
if timeout:
self.timer = Timer.after(timeout)
else:
self.timer = NeverExpires()
def expired(self):
if self.timer.expired():
raise LockTimeout(
'Timeout acquiring lock for %(session_id)s' % vars(self))
return False
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