Added max_concurrent argument to background tag decorator

import logging

import weakref

import threading

from functools import partial

from functools import partial, update_wrapper

from itertools import chain

from collections import defaultdict

    return decorator

def background(func):

def background(max_concurrent=None):

    def background_decorator(func):

        func.background = True

        semaphore = threading.Semaphore(max_concurrent) if max_concurrent else None

        if semaphore is not None:

            if not len(inspect.getargspec(func).args):

                def wrapper():

                    with semaphore:

                        return func()

            else:

                def wrapper(dom):

                    with semaphore:

                        return func(dom)

            wrapper = update_wrapper(wrapper, func)

            return wrapper

        else:

            return func

    return background_decorator

def get_tags(tags_dict, tags=None):

    """Helper to get tags.