/*
* Copyright (c) 2022 Vaughn Nugent
*
* Library: VNLib
* Package: VNLib.Plugins.Sessions.Cache.Client
* File: SessionCacheClient.cs
*
* SessionCacheClient.cs is part of VNLib.Plugins.Sessions.Cache.Client which is part of the larger
* VNLib collection of libraries and utilities.
*
* VNLib.Plugins.Sessions.Cache.Client 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.Plugins.Sessions.Cache.Client 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.Threading.Tasks;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using VNLib.Net.Http;
using VNLib.Utils.Async;
using VNLib.Utils.Logging;
using VNLib.Utils.Memory.Caching;
using VNLib.Plugins.Essentials.Sessions;
namespace VNLib.Plugins.Sessions.Cache.Client
{
///
/// A client that allows access to sessions located on external servers
///
public abstract class SessionCacheClient : ICacheHolder
{
public class LRUSessionStore : LRUCache, ICacheHolder where T : ISession
{
internal AsyncQueue ExpiredSessions { get; }
///
public override bool IsReadOnly => false;
///
protected override int MaxCapacity { get; }
public LRUSessionStore(int maxCapacity) : base(StringComparer.Ordinal)
{
MaxCapacity = maxCapacity;
ExpiredSessions = new (true, true);
}
///
protected override bool CacheMiss(string key, [NotNullWhen(true)] out T? value)
{
value = default;
return false;
}
///
protected override void Evicted(ref KeyValuePair evicted)
{
//add to queue, the list lock should be held during this operatio
_ = ExpiredSessions.TryEnque(evicted.Value);
}
///
public void CacheClear()
{
foreach (KeyValuePair value in List)
{
KeyValuePair onStack = value;
Evicted(ref onStack);
}
Clear();
}
///
public void CacheHardClear()
{
CacheClear();
}
}
protected readonly LRUSessionStore CacheTable;
protected readonly object CacheLock;
protected readonly int MaxLoadedEntires;
///
/// The client used to communicate with the cache server
///
protected IRemoteCacheStore Store { get; }
///
/// Gets a value that determines if the backing is connected
/// to a server
///
public bool IsConnected => Store.IsConnected;
///
/// Initializes a new
///
///
/// The maximum number of sessions to keep in memory
protected SessionCacheClient(IRemoteCacheStore client, int maxCacheItems)
{
MaxLoadedEntires = maxCacheItems;
CacheLock = new();
CacheTable = new(maxCacheItems);
Store = client;
}
private ulong _waitingCount;
///
/// The number of pending connections waiting for results from the cache server
///
public ulong WaitingConnections => _waitingCount;
///
/// Attempts to get a session from the cache identified by its sessionId asynchronously
///
/// The connection/request to attach the session to
/// The ID of the session to retrieve
/// A token to cancel the operation
/// A that resolves the remote session
///
public virtual async ValueTask GetSessionAsync(IHttpEvent entity, string sessionId, CancellationToken cancellationToken)
{
try
{
RemoteSession? session;
//Aquire lock on cache
lock (CacheLock)
{
//See if session is loaded into cache
if (!CacheTable.TryGetValue(sessionId, out session))
{
//Init new record
session = SessionCtor(sessionId);
//Add to cache
CacheTable.Add(session.SessionID, session);
}
//Valid entry found in cache
}
//Inc waiting count
Interlocked.Increment(ref _waitingCount);
try
{
//Load session-data
await session.WaitAndLoadAsync(entity, cancellationToken);
return session;
}
catch
{
//Remove the invalid cached session
lock (CacheLock)
{
_ = CacheTable.Remove(sessionId);
}
throw;
}
finally
{
//Dec waiting count
Interlocked.Decrement(ref _waitingCount);
}
}
catch (SessionException)
{
throw;
}
catch (OperationCanceledException)
{
throw;
}
//Wrap exceptions
catch (Exception ex)
{
throw new SessionException("An unhandled exception was raised", ex);
}
}
///
/// Gets a new instances for the given sessionId,
/// and places it a the head of internal cache
///
/// The session identifier
/// The new session for the given ID
protected abstract RemoteSession SessionCtor(string sessionId);
///
/// Begins waiting for expired sessions to be evicted from the cache table that
/// may have pending synchronization operations
///
///
///
///
public async Task CleanupExpiredSessionsAsync(ILogProvider log, CancellationToken token)
{
while (true)
{
try
{
//Wait for expired session and dispose it
using RemoteSession session = await CacheTable.ExpiredSessions.DequeueAsync(token);
//Obtain lock on session
await session.WaitOneAsync(CancellationToken.None);
log.Verbose("Removed expired session {id}", session.SessionID);
}
catch (OperationCanceledException)
{
break;
}
catch(Exception ex)
{
log.Error(ex);
}
}
}
///
public void CacheClear()
{
}
///
public void CacheHardClear()
{
//Cleanup cache when disconnected
lock (CacheLock)
{
CacheTable.CacheHardClear();
}
}
}
}