utils.py

#!/usr/bin/env python
#coding=utf8

'''
Some helpers used by cc-server.
'''

class Acquires(object):

    '''
    Context manager used to acquire more than one lock at once. It works rely
    on the fact that if locks are always acquired in the same order, we can't
    enter in a deadlock situation.

    Usage is very simple:

    >>> a = Lock()
    >>> b = Lock()
    >>> with Acquires(b, a):
    ...     print 'locked'
    ...

    .. seealso::
        http://dabeaz.blogspot.com/2009/11/python-thread-deadlock-avoidance_20.html
    '''

    def __init__(self, *locks):
        self._locks = sorted(locks, key=lambda x: id(x))

    def __enter__(self):
        for lock in self._locks:
            lock.acquire()

    def __exit__(self, exc_type, exc_value, traceback):
        for lock in self._locks:
            lock.release()