using System;
using System.Linq;
using System.Collections.Generic;
using System.Collections.Concurrent;
using System.Reflection;
using System.Linq.Expressions;
using System.Threading;
using System.Threading.Tasks;

using var gate = new SemaphoreSlim(1, 1);
var first = await Lease.TakeAsync(gate);
Task<Lease> pending = Lease.TakeAsync(gate).AsTask();
Console.WriteLine($"waiting:{!pending.IsCompleted}");
await first.DisposeAsync(); await first.DisposeAsync();
var second = await pending;
Console.WriteLine($"inside:{gate.CurrentCount}");
await second.DisposeAsync(); await second.DisposeAsync();
Console.WriteLine($"final:{gate.CurrentCount}");
sealed class Lease : IAsyncDisposable
{
    private SemaphoreSlim? gate;
    private Lease(SemaphoreSlim gate) { this.gate = gate; }
    public static async ValueTask<Lease> TakeAsync(SemaphoreSlim gate) { await gate.WaitAsync().ConfigureAwait(false); return new Lease(gate); }
    public ValueTask DisposeAsync() { Interlocked.Exchange(ref gate, null)?.Release(); return ValueTask.CompletedTask; }
}