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/*
* Copyright (c) 2023 Vaughn Nugent
*
* Library: VNLib
* Package: VNLib.Plugins.Sessions.Cache.Client
* File: SessionSerializer.cs
*
* SessionSerializer.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.Utils.Async;
namespace VNLib.Plugins.Sessions.Cache.Client
{
/// <summary>
/// Concrete <see cref="ISessionSerialzer{TSession}"/> that provides
/// access serialization for session types
/// </summary>
/// <typeparam name="TSession">The session type</typeparam>
public class SessionSerializer<TSession> : AsyncAccessSerializer<TSession>, ISessionSerialzer<TSession> where TSession : IRemoteSession
{
/*
* This implementation uses an internal store for wait entires
* that uses a string key instead of using the moniker directly,
* but inherits the concrete serialzer class to reuse the built
* in helper types and methods in the AsyncAccessSerializer class.
*
* The utils library is also currently the only lib that has
* automated testing, so that helps us.
*
* This is to allow sessions to be recovered from their session
* id instead of a session instance. All public api method calls
* are intercepted and routed to the internal wait table
*/
private readonly Dictionary<string, WaitEntry> _waitTable;
/// <summary>
/// Initializes a new <see cref="SessionSerializer{TSession}"/>
/// </summary>
/// <param name="poolCapacity">The maximum number of wait entry instances to hold in memory cache</param>
public SessionSerializer(int poolCapacity) : base(poolCapacity, 0, null)
{
//Session-ids are security senstive, we must use ordinal(binary) string comparison
_waitTable = new Dictionary<string, WaitEntry>(poolCapacity, StringComparer.Ordinal);
}
///<inheritdoc/>
public virtual bool TryGetSession(string sessionId, [NotNullWhen(true)] out TSession? session)
{
lock (StoreLock)
{
//Try to see if an entry is loaded, and get the session
bool result = _waitTable.TryGetValue(sessionId, out WaitEntry? entry);
session = result ? entry!.Moniker : default;
return result;
}
}
///<inheritdoc/>
public override Task WaitAsync(TSession moniker, CancellationToken cancellation = default)
{
//Token must not be cancelled
cancellation.ThrowIfCancellationRequested();
WaitEnterToken token;
WaitEntry? wait;
if (cancellation.CanBeCanceled)
{
lock (StoreLock)
{
//See if the entry already exists, otherwise get a new wait entry
if (!_waitTable.TryGetValue(moniker.SessionID, out wait))
{
GetWaitEntry(ref wait, moniker);
//Add entry to store
_waitTable[moniker.SessionID] = wait;
}
//Get waiter before leaving lock
wait.ScheduleWait(cancellation, out token);
}
//Enter wait and setup cancellation continuation
return EnterCancellableWait(in token, wait);
}
else
{
lock (StoreLock)
{
//See if the entry already exists, otherwise get a new wait entry
if (!WaitTable.TryGetValue(moniker, out wait))
{
GetWaitEntry(ref wait, moniker);
//Add entry to store
WaitTable[moniker] = wait;
}
//Get waiter before leaving lock
wait.ScheduleWait(out token);
}
//Enter the waiter without any cancellation support
return token.EnterWaitAsync();
}
}
///<inheritdoc/>
public override void Release(TSession moniker)
{
WaitReleaseToken releaser;
do
{
lock (StoreLock)
{
WaitEntry entry = _waitTable[moniker.SessionID];
//Call release while holding store lock
if (entry.ExitWait(out releaser) == 0)
{
//No more waiters
_waitTable.Remove(moniker.SessionID);
/*
* We must release the semaphore before returning to pool,
* its safe because there are no more waiters
*/
releaser.Release();
ReturnEntry(entry);
//already released
releaser = default;
}
}
//See base class for why we need to loop
} while (!releaser.Release());
}
///<inheritdoc/>
public new void CacheHardClear()
{
base.CacheHardClear();
lock (StoreLock)
{
_waitTable.TrimExcess();
}
}
}
}
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