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/*
* Copyright (c) 2023 Vaughn Nugent
*
* Library: VNLib
* Package: VNLib.Data.Caching.Providers.VNCache
* File: ClusterNodeIndex.cs
*
* ClusterNodeIndex.cs is part of VNLib.Data.Caching.Providers.VNCache which is part of the larger
* VNLib collection of libraries and utilities.
*
* VNLib.Data.Caching.Providers.VNCache 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.
*
* VNLib.Data.Caching.Providers.VNCache 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.Threading;
using System.Text.Json;
using System.Reflection;
using System.Threading.Tasks;
using VNLib.Utils.Logging;
using VNLib.Utils.Resources;
using VNLib.Data.Caching.Extensions;
using VNLib.Data.Caching.Extensions.Clustering;
using VNLib.Plugins.Extensions.Loading.Events;
namespace VNLib.Data.Caching.Providers.VNCache.Clustering
{
internal static class ClusterNodeIndex
{
const string APP_DOMAIN_KEY = "vnlib.data.caching.providers.vncache";
/*
* Safeley determines if an instance of a node index already exists in the app domain
* if so it returns that instance, otherwise it creates a new index instance and stores
* it in the app domain.
*/
public static IClusterNodeIndex CreateIndex(CacheClientConfiguration config)
{
//Create a named semaphore to ensure only one index is created per app domain
using Semaphore sm = new (1, 1, APP_DOMAIN_KEY, out _);
if (!sm.WaitOne(500))
{
throw new TimeoutException("Failed to access the Cluster index shared semaphore");
}
try
{
//Try to get an existing index from the app domain
object? remoteIndex = AppDomain.CurrentDomain.GetData(APP_DOMAIN_KEY);
if (remoteIndex == null)
{
//Create a new index and store it in the app domain
IClusterNodeIndex index = new LocalHandler(config);
AppDomain.CurrentDomain.SetData(APP_DOMAIN_KEY, index);
return index;
}
else
{
//Use the existing index
return new RemoteHandler(remoteIndex);
}
}
finally
{
sm.Release();
}
}
record class LocalHandler(CacheClientConfiguration Config) : IClusterNodeIndex, IIntervalScheduleable
{
private Task _currentUpdate = Task.CompletedTask;
///<inheritdoc/>
public CacheNodeAdvertisment? GetNextNode()
{
//Get all nodes
CacheNodeAdvertisment[] ads = Config.NodeCollection.GetAllNodes();
//Just get a random node from the collection for now
return ads.Length > 0 ? ads.SelectRandom() : null;
}
///<inheritdoc/>
public Task WaitForDiscoveryAsync(CancellationToken cancellationToken) => _currentUpdate;
///<inheritdoc/>
public Task OnIntervalAsync(ILogProvider log, CancellationToken cancellationToken)
{
//Run discovery operation and update the task
_currentUpdate = Config.DiscoverNodesAsync(cancellationToken);
return Task.CompletedTask;
}
/*
* Private methods that are called via reflection
* by remote instances of the index
*/
internal string? SerializeNextNode()
{
CacheNodeAdvertisment? nextNode = GetNextNode();
return nextNode == null ? null : JsonSerializer.Serialize(nextNode);
}
}
class RemoteHandler : IClusterNodeIndex
{
private readonly Func<string?> _remoteSerializer;
private readonly Func<CancellationToken, Task> _waitTask;
public RemoteHandler(object RemoteIndex)
{
//get the serializer method
_remoteSerializer = ManagedLibrary.GetMethod<Func<string?>>(RemoteIndex, nameof(LocalHandler.SerializeNextNode), BindingFlags.NonPublic);
//get the wait task method
_waitTask = ManagedLibrary.GetMethod<Func<CancellationToken, Task>>(RemoteIndex, nameof(WaitForDiscoveryAsync), BindingFlags.Public);
}
///<inheritdoc/>
public CacheNodeAdvertisment? GetNextNode()
{
//Deserialize the next node from the remote index
string? nexNode = _remoteSerializer();
return nexNode == null ? null : JsonSerializer.Deserialize<CacheNodeAdvertisment>(nexNode);
}
///<inheritdoc/>
public Task WaitForDiscoveryAsync(CancellationToken cancellationToken) => _waitTask(cancellationToken);
}
}
}
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