Latest working draft

1 files changed, 263 insertions, 0 deletions

diff --git a/plugins/ObjectCacheServer/src/Cache/CacheEventQueueManager.cs b/plugins/ObjectCacheServer/src/Cache/CacheEventQueueManager.cs
new file mode 100644
index 0000000..ad0eb5a
--- /dev/null
+++ b/plugins/ObjectCacheServer/src/Cache/CacheEventQueueManager.cs
@@ -0,0 +1,263 @@
+/*
+* Copyright (c) 2023 Vaughn Nugent
+* 
+* Library: VNLib
+* Package: ObjectCacheServer
+* File: CacheEventQueueManager.cs 
+*
+* CacheEventQueueManager.cs is part of ObjectCacheServer which is 
+* part of the larger VNLib collection of libraries and utilities.
+*
+* ObjectCacheServer is free software: you can redistribute it and/or modify 
+* it under the terms of the GNU Affero General Public License as 
+* published by the Free Software Foundation, either version 3 of the
+* License, or (at your option) any later version.
+*
+* ObjectCacheServer is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+* GNU Affero General Public License for more details.
+*
+* You should have received a copy of the GNU Affero General Public License
+* along with this program.  If not, see https://www.gnu.org/licenses/.
+*/
+
+using System;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using System.Threading.Channels;
+using System.Collections.Generic;
+
+using VNLib.Plugins;
+using VNLib.Utils.Async;
+using VNLib.Utils.Logging;
+using VNLib.Utils.Extensions;
+using VNLib.Plugins.Extensions.Loading;
+using VNLib.Plugins.Extensions.Loading.Events;
+
+
+namespace VNLib.Data.Caching.ObjectCache.Server.Cache
+{
+    internal sealed class CacheEventQueueManager : ICacheEventQueueManager, IDisposable, IIntervalScheduleable
+    {
+        private readonly int MaxQueueDepth;
+
+        private readonly object SubLock;
+        private readonly LinkedList<NodeQueue> Subscribers;
+
+        private readonly object StoreLock;
+        private readonly Dictionary<string, NodeQueue> QueueStore;
+
+
+        public CacheEventQueueManager(PluginBase plugin)
+        {
+            //Get node config
+            NodeConfig config = plugin.GetOrCreateSingleton<NodeConfig>();
+
+            //Get max queue depth
+            MaxQueueDepth = config.MaxQueueDepth;
+
+            /*
+             * Schedule purge interval to clean up stale queues
+             */
+            plugin.ScheduleInterval(this, config.EventQueuePurgeInterval);
+
+            SubLock = new();
+            Subscribers = new();
+
+            StoreLock = new();
+            QueueStore = new(StringComparer.OrdinalIgnoreCase);
+        }
+
+        ///<inheritdoc/>
+        public IPeerEventQueue Subscribe(ICachePeer peer)
+        {
+            NodeQueue? nq;
+
+            bool isNew = false;
+
+            //Enter sync lock
+            lock (StoreLock)
+            {
+                //Try to recover the queue for the node
+                if (!QueueStore.TryGetValue(peer.NodeId, out nq))
+                {
+                    //Create new queue
+                    nq = new(peer.NodeId, MaxQueueDepth);
+                    QueueStore.Add(peer.NodeId, nq);
+                    isNew = true;
+                }
+
+                //Increment listener count
+                nq.Listeners++;
+            }
+
+            //Publish new peer to subscribers list
+            if (isNew)
+            {
+                lock (SubLock)
+                {
+                    //Add peer to subscribers list
+                    Subscribers.AddLast(nq);
+                }
+            }
+
+            //Return the node's queue
+            return nq;
+        }
+
+        ///<inheritdoc/>
+        public void Unsubscribe(ICachePeer peer)
+        {
+            //Detach a listener for a node
+            lock (StoreLock)
+            {
+                //Get the queue and decrement the listener count
+                NodeQueue nq = QueueStore[peer.NodeId];
+                nq.Listeners--;
+            }
+        }
+
+        ///<inheritdoc/>
+        public void PublishSingle(ChangeEvent change)
+        {
+            //Wait to enter the sub lock
+            lock (SubLock)
+            {
+                //Loop through ll the fast way
+                LinkedListNode<NodeQueue>? q = Subscribers.First;
+
+                while (q != null)
+                {
+                    //Pub single event node
+                    q.Value.PublishChange(change);
+
+                    //Get next queue
+                    q = q.Next;
+                }
+            }
+        }
+
+        ///<inheritdoc/>
+        public void PublishMultiple(Span<ChangeEvent> changes)
+        {
+            //Wait to enter the sub lock
+            lock (SubLock)
+            {
+                //Loop through ll the fast way
+                LinkedListNode<NodeQueue>? q = Subscribers.First;
+
+                while (q != null)
+                {
+                    //Publish multiple
+                    q.Value.PublishChanges(changes);
+
+                    //Get next queue
+                    q = q.Next;
+                }
+            }
+        }
+
+        ///<inheritdoc/>
+        public void PurgeStaleSubscribers()
+        {
+            //Enter locks
+            lock (SubLock)
+                lock (StoreLock)
+                {
+                    //Get all stale queues (queues without listeners)
+                    NodeQueue[] staleQueues = QueueStore.Values.Where(static nq => nq.Listeners == 0).ToArray();
+
+                    foreach (NodeQueue nq in staleQueues)
+                    {
+                        //Remove from store
+                        QueueStore.Remove(nq.NodeId);
+
+                        //remove from subscribers
+                        Subscribers.Remove(nq);
+                    }
+                }
+        }
+
+        //Interval to purge stale subscribers
+        Task IIntervalScheduleable.OnIntervalAsync(ILogProvider log, CancellationToken cancellationToken)
+        {
+            log.Debug("Purging stale peer event queues");
+
+            PurgeStaleSubscribers();
+
+            return Task.CompletedTask;
+        }
+
+        void IDisposable.Dispose()
+        {
+            QueueStore.Clear();
+            Subscribers.Clear();
+        }
+
+        /*
+         * Holds queues for each node and keeps track of the number of listeners
+         * attached to the queue
+         */
+
+        private sealed class NodeQueue : IPeerEventQueue
+        {
+            public int Listeners;
+
+            public string NodeId { get; }
+
+            public AsyncQueue<ChangeEvent> Queue { get; }
+
+            public NodeQueue(string nodeId, int maxDepth)
+            {
+                NodeId = nodeId;
+
+                /*
+                 * Create a bounded channel that acts as a lru and evicts 
+                 * the oldest item when the queue is full
+                 * 
+                 * There will also only ever be a single thread writing events 
+                 * to the queue
+                 */
+
+                BoundedChannelOptions queueOptions = new(maxDepth)
+                {
+                    AllowSynchronousContinuations = true,
+                    SingleReader = false,
+                    SingleWriter = true,
+                    //Drop oldest item in queue if full
+                    FullMode = BoundedChannelFullMode.DropOldest,
+                };
+
+                //Init queue/channel
+                Queue = new(queueOptions);
+            }
+
+            public void PublishChange(ChangeEvent change)
+            {
+                Queue.TryEnque(change);
+            }
+
+            public void PublishChanges(Span<ChangeEvent> changes)
+            {
+                for (int i = 0; i < changes.Length; i++)
+                {
+                    Queue.TryEnque(changes[i]);
+                }
+            }
+
+            ///<inheritdoc/>
+            public ValueTask<ChangeEvent> DequeueAsync(CancellationToken cancellation)
+            {
+                return Queue.DequeueAsync(cancellation);
+            }
+
+            ///<inheritdoc/>
+            public bool TryDequeue(out ChangeEvent change)
+            {
+                return Queue.TryDequeue(out change);
+            }
+        }
+    }
+}