// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Razor.Utilities;
 
namespace Microsoft.CodeAnalysis.Razor.Threading;
 
internal static class SemaphoreSlimExtensions
{
    public static SemaphoreDisposer DisposableWait(this SemaphoreSlim semaphore, CancellationToken cancellationToken = default)
    {
        semaphore.Wait(cancellationToken);
        return new SemaphoreDisposer(semaphore);
    }
 
    public static async ValueTask<SemaphoreDisposer> DisposableWaitAsync(this SemaphoreSlim semaphore, CancellationToken cancellationToken = default)
    {
        await semaphore.WaitAsync(cancellationToken).ConfigureAwait(false);
        return new SemaphoreDisposer(semaphore);
    }
 
    [NonCopyable]
    internal struct SemaphoreDisposer : IDisposable
    {
        private SemaphoreSlim? _semaphore;
 
        public SemaphoreDisposer(SemaphoreSlim semaphore)
        {
            _semaphore = semaphore;
        }
 
        public void Dispose()
        {
            // Officially, Dispose() being called more than once is allowable, but in this case
            // if that were to ever happen that means something is very, very wrong. Since it's an internal
            // type, better to be strict.
 
            // Nulling this out also means it's a bit easier to diagnose some async deadlocks; if you have an
            // async deadlock where a SemaphoreSlim is held but you're unsure why, as long all the users of the
            // SemaphoreSlim used the Disposable helpers, you can search memory and find the instance that
            // is pointing to the SemaphoreSlim that hasn't nulled out this field yet; in that case you know
            // that's holding the lock and can figure out who is holding that SemaphoreDisposer.
            var semaphoreToDispose = Interlocked.Exchange(ref _semaphore, null);
 
            if (semaphoreToDispose is null)
            {
                throw new ObjectDisposedException($"Somehow a {nameof(SemaphoreDisposer)} is being disposed twice.");
            }
 
            semaphoreToDispose.Release();
        }
    }
}