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#! /usr/bin/env python
"""Provide way to add timeout specifications to arbitrary functions.

There are many ways to add a timeout to a function, but no solution
is both cross-platform and capable of terminating the procedure. This
module use the multiprocessing module to solve both of those problems."""

################################################################################

__author__ = 'Stephen "Zero" Chappell <Noctis.Skytower@gmail.com>'
__date__ = '11 February 2010'
__version__ = '$Revision: 3 $'

################################################################################

import inspect
import sys
import time
import multiprocessing

################################################################################

def add_timeout(function, limit=60):
"""Add a timeout parameter to a function and return it.

It is illegal to pass anything other than a function as the first
parameter. If the limit is not given, it gets a default value equal
to one minute. The function is wrapped and returned to the caller."""
assert inspect.isfunction(function)
if limit <= 0:
raise ValueError()
return _Timeout(function, limit)

class NotReadyError(Exception): pass

################################################################################

def _target(queue, function, *args, **kwargs):
"""Run a function with arguments and return output via a queue.

This is a helper function for the Process created in _Timeout. It runs
the function with positional arguments and keyword arguments and then
returns the function's output by way of a queue. If an exception gets
raised, it is returned to _Timeout to be raised by the value property."""
try:
queue.put((True, function(*args, **kwargs)))
except:
queue.put((False, sys.exc_info()[1]))

class _Timeout:

"""Wrap a function and add a timeout (limit) attribute to it.

Instances of this class are automatically generated by the add_timeout
function defined above. Wrapping a function allows asynchronous calls
to be made and termination of execution after a timeout has passed."""

def __init__(self, function, limit):
"""Initialize instance in preparation for being called."""
self.__limit = limit
self.__function = function
self.__timeout = time.clock()
self.__process = multiprocessing.Process()
self.__queue = multiprocessing.Queue()

def __call__(self, *args, **kwargs):
"""Execute the embedded function object asynchronously.

The function given to the constructor is transparently called and
requires that "ready" be intermittently polled. If and when it is
True, the "value" property may then be checked for returned data."""
self.cancel()
self.__queue = multiprocessing.Queue(1)
args = (self.__queue, self.__function) + args
self.__process = multiprocessing.Process(target=_target,
args=args,
kwargs=kwargs)
self.__process.daemon = True
self.__process.start()
self.__timeout = self.__limit + time.clock()

def cancel(self):
"""Terminate any possible execution of the embedded function."""
if self.__process.is_alive():
self.__process.terminate()

@property
def ready(self):
"""Read-only property indicating status of "value" property."""
if self.__queue.full():
return True
elif not self.__queue.empty():
return True
elif self.__timeout < time.clock():
self.cancel()
else:
return False

@property
def value(self):
"""Read-only property containing data returned from function."""
if self.ready is True:
flag, load = self.__queue.get()
if flag:
return load
raise load
raise NotReadyError()

def __get_limit(self):
return self.__limit

def __set_limit(self, value):
if value <= 0:
raise ValueError()
self.__limit = value

limit = property(__get_limit, __set_limit,
doc="Property for controlling the value of the timeout.")

Change log

r2 by Noctis.Skytower on Mar 15, 2010   Diff
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