Added AcquiresAllOrNone class in utils.

Some helpers used by cc-server.

'''

from threading import Lock

class Acquires(object):

    '''

    def __exit__(self, exc_type, exc_value, traceback):

        for lock in self._locks:

            lock.release()

class AcquiresAllOrNone(Acquires):

    '''

    Class that extend Acquires to allow to release all lock if one of them

    is not free.

    '''

    # Global acquire lock:

    acquirelock = Lock()

    def __enter__(self):

        while True:

            with self.acquirelock:

                acquired = []

                for lock in self._locks:

                    if not lock.acquire(False):

                        for lock_acquired in acquired:

                            lock_acquired.release()

                        break

                    else:

                        acquired.append(lock)

                else:

                    break