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# Copyright 2022-2023 ETSI TeraFlowSDN - TFS OSG (https://tfs.etsi.org/)
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#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# MutexQueues:
# ------------
# This class enables to schedule and serialize operations concurrently issued
# over a number of resources. For instance, when multiple components want to
# configure devices through the Device component, configuration operations
# have to be serialized to prevent data corruptions, and race conditions, etc.
# Usage Example:
# class Servicer():
# def __init__(self):
# # init other stuff
# self.drivers = dict()
# self.mutex_queues = MutexQueues()
#
# def configure_device(self, device_uuid, settings):
# self.mutex_queues.wait_my_turn(device_uuid)
# driver = self.drivers.get(device_uuid)
# if driver is None:
# driver = Driver(device_uuid)
# self.drivers[device_uuid] = driver
# driver.configure(settings)
# self.mutex_queues.signal_done(device_uuid)
import threading
from queue import Queue
from typing import Dict
class MutexQueues:
def __init__(self) -> None:
# lock to protect dictionary updates
self.lock = threading.Lock()
# dictionaty of queues of mutexes: queue_name => queue[mutex]
# first mutex is the running one
self.mutex_queues : Dict[str, Queue[threading.Event]] = dict()
def wait_my_turn(self, queue_name : str) -> None:
# create my mutex and enqueue it
mutex = threading.Event()
with self.lock:
queue : Queue = self.mutex_queues.setdefault(queue_name, Queue())
first_in_queue = (queue.qsize() == 0)
queue.put_nowait(mutex)
# if I'm the first in the queue upon addition, means there are no running tasks
# directly return without waiting
if first_in_queue: return
# otherwise, wait for my turn in the queue
mutex.wait()
def signal_done(self, queue_name : str) -> None:
# I'm done with my work
with self.lock:
queue : Queue = self.mutex_queues.setdefault(queue_name, Queue())
# remove muself from the queue
queue.get_nowait()
# if there are no other tasks queued, return
if queue.qsize() == 0: return
# otherwise, signal the next task in the queue to start
next_mutex : threading.Event = queue.queue[0]
next_mutex.set()