ReflectionUnlocker.cs

// Copyright 2019 Emzi0767
// 
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// 
//   http://www.apache.org/licenses/LICENSE-2.0
// 
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/*
 * Documentation of all the relevant types:
 *
 * System.Threading.Tasks.Task
 *   https://docs.microsoft.com/en-us/dotnet/api/system.threading.tasks.task?view=netcore-2.2
 * 
 * System.Threading.Tasks.TaskContinuationOptions
 *   https://docs.microsoft.com/en-us/dotnet/api/system.threading.tasks.taskcontinuationoptions?view=netcore-2.2
 *
 * System.Threading.SemaphoreSlim
 *   https://docs.microsoft.com/en-us/dotnet/api/system.threading.semaphoreslim?view=netcore-2.2
 *
 * System.Threading.CancellationToken
 *   https://docs.microsoft.com/en-us/dotnet/api/system.threading.cancellationtoken?view=netcore-2.2
 *
 * System.Threading.CancellationTokenSource
 *   https://docs.microsoft.com/en-us/dotnet/api/system.threading.cancellationtokensource?view=netcore-2.2
 *
 * DSharpPlus.DiscordClient
 *   https://dsharpplus.github.io/api/DSharpPlus.DiscordClient.html
 */

/* THE FOLLOWING ASSUMES EXISTENCE OF FOLLOWING PROPERTIES */
SemaphoreSlim LockerInstance { get; set; }
CancellationTokenSource TokenSource { get; set; }
CancellationToken Token => TokenSource.Token;
 
/* OBTAINING THE LOCKER INSTANCE */
using System.Reflection;
using System.Threading;

var t = typeof(DiscordClient);
var prop = t.GetProperty("ConnectionSemaphore", BindingFlags.NonPublic | BindingFlags.Static);
LockerInstance = prop.GetValue(null) as SemaphoreSlim;

/* DISCORD SOCKET EVENT HANDLERS */
Task DiscordSocketClosed(SocketCloseEventArgs e) // handles DiscordClient#SocketClosed
{
    try 
    {
        // dispose of the token source - it will leak otherwise
        TokenSource?.Cancel();
        TokenSource?.Dispose(); 
    } 
    catch { /* swallow exceptions since they're not relevant */ }
    
    TokenSource = new CancellationTokenSource();
    UnlockTask = Task.Delay(TimeSpan.FromSeconds(15 /* This can technically be anything so long as it's >=5 */), Token);
    UnlockTask.ContinueWith(UnlockerContinuation, TokenSource, TaskContinuationOptions.OnlyOnRanToCompletion);
    return Task.CompletedTask;
    
    void UnlockerContinuation(Task t, object state)
    {
        if (!(state is CancellationTokenSource cts))
            return;
        
        try
        {
            // they are not null, otherwise it would not match
            cts.Cancel();
            cts.Dispose();
        }
        catch { /* swallow exceptions since they're not relevant */ }
    }
}

Task DiscordSocketOpened() // handles DiscordClient#SocketOpened
{
    try
    {
        // canel the token and dispose it - we don't need to unlock since connection attempt seems to have been successful
        TokenSource.Cancel();
        TokenSource.Dispose();
    }
    catch { /* swallow exceptions since they're not relevant */ }
}