System.Net.TimerThread.GetOrCreateQueue C# (CSharp) Method

        internal static Queue GetOrCreateQueue(int durationMilliseconds)
        {
            if (durationMilliseconds == Timeout.Infinite)
            {
                return new InfiniteTimerQueue();
            }

            if (durationMilliseconds < 0)
            {
                throw new ArgumentOutOfRangeException(nameof(durationMilliseconds));
            }

            TimerQueue queue;
            WeakReference weakQueue = (WeakReference)s_QueuesCache[durationMilliseconds];
            if (weakQueue == null || (queue = (TimerQueue)weakQueue.Target) == null)
            {
                lock (s_NewQueues)
                {
                    weakQueue = (WeakReference)s_QueuesCache[durationMilliseconds];
                    if (weakQueue == null || (queue = (TimerQueue)weakQueue.Target) == null)
                    {
                        queue = new TimerQueue(durationMilliseconds);
                        weakQueue = new WeakReference(queue);
                        s_NewQueues.AddLast(weakQueue);
                        s_QueuesCache[durationMilliseconds] = weakQueue;

                        // Take advantage of this lock to periodically scan the table for garbage.
                        if (++s_CacheScanIteration % c_CacheScanPerIterations == 0)
                        {
                            List<int> garbage = new List<int>();
                            foreach (DictionaryEntry pair in s_QueuesCache)
                            {
                                if (((WeakReference)pair.Value).Target == null)
                                {
                                    garbage.Add((int)pair.Key);
                                }
                            }
                            for (int i = 0; i < garbage.Count; i++)
                            {
                                s_QueuesCache.Remove(garbage[i]);
                            }
                        }
                    }
                }
            }

            return queue;
        }

        internal void Close()
        {
            site.Close();

            // Can't call AppDomain.Unload() from a user thread.
            TimerThread.GetOrCreateQueue(0).CreateTimer(new TimerThread.Callback(CloseAppDomainCallback), appDomainIndex);
            GC.SuppressFinalize(this);
        }