ASP.NET Core 3.x 并发限制的实现代码

    public void ConfigureServices(IServiceCollection services)
    {
      services.AddQueuePolicy(options =>
      {
        //最大并发请求数
        options.MaxConcurrentRequests = 2;
        //请求队列长度限制
        options.RequestQueueLimit = 1;
      });
      services.AddControllers();
    }
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
      //添加并发限制中间件
      app.UseConcurrencyLimiter();
      app.Run(async context =>
      {
        Task.Delay(100).Wait(); // 100ms sync-over-async

        await context.Response.WriteAsync("Hello World!");
      });
      if (env.IsDevelopment())
      {
        app.UseDeveloperExceptionPage();
      }

      app.UseHttpsRedirection();

      app.UseRouting();

      app.UseAuthorization();

      app.UseEndpoints(endpoints =>
      {
        endpoints.MapControllers();
      });
    }   

 public static IServiceCollection AddQueuePolicy(this IServiceCollection services, Action<QueuePolicyOptions> configure)
{
    services.Configure(configure);
    services.AddSingleton<IQueuePolicy, QueuePolicy>();
    return services;
}

   /// <summary>
    ///   构造方法(初始化Queue策略)
    /// </summary>
    /// <param name="options"></param>
    public QueuePolicy(IOptions<QueuePolicyOptions> options)
    {
      _maxConcurrentRequests = options.Value.MaxConcurrentRequests;
      if (_maxConcurrentRequests <= 0)
      {
        throw new ArgumentException(nameof(_maxConcurrentRequests), "MaxConcurrentRequests must be a positive integer.");
      }

      _requestQueueLimit = options.Value.RequestQueueLimit;
      if (_requestQueueLimit < 0)
      {
        throw new ArgumentException(nameof(_requestQueueLimit), "The RequestQueueLimit cannot be a negative number.");
      }
      //使用SemaphoreSlim来限制任务最大个数
      _serverSemaphore = new SemaphoreSlim(_maxConcurrentRequests);
    }

    /// <summary>
    /// Invokes the logic of the middleware.
    /// </summary>
    /// <param name="context">The <see cref="HttpContext"/>.</param>
    /// <returns>A <see cref="Task"/> that completes when the request leaves.</returns>
    public async Task Invoke(HttpContext context)
    {
      var waitInQueueTask = _queuePolicy.TryEnterAsync();

      // Make sure we only ever call GetResult once on the TryEnterAsync ValueTask b/c it resets.
      bool result;

      if (waitInQueueTask.IsCompleted)
      {
        ConcurrencyLimiterEventSource.Log.QueueSkipped();
        result = waitInQueueTask.Result;
      }
      else
      {
        using (ConcurrencyLimiterEventSource.Log.QueueTimer())
        {
          result = await waitInQueueTask;
        }
      }

      if (result)
      {
        try
        {
          await _next(context);
        }
        finally
        {
          _queuePolicy.OnExit();
        }
      }
      else
      {
        ConcurrencyLimiterEventSource.Log.RequestRejected();
        ConcurrencyLimiterLog.RequestRejectedQueueFull(_logger);
        context.Response.StatusCode = StatusCodes.Status503ServiceUnavailable;
        await _onRejected(context);
      }
    }

 if (result)
 {
     try
     {
       await _next(context);
     }
     finally
    {
      _queuePolicy.OnExit();
    }
    }
    else
    {
      ConcurrencyLimiterEventSource.Log.RequestRejected();
      ConcurrencyLimiterLog.RequestRejectedQueueFull(_logger);
      context.Response.StatusCode = StatusCodes.Status503ServiceUnavailable;
      await _onRejected(context);
    }

 lock (_totalRequestsLock)
  {
    if (TotalRequests >= _requestQueueLimit + _maxConcurrentRequests)
    {
       return false;
    }
      TotalRequests++;
    }
    //异步等待进入信号量，如果没有线程被授予对信号量的访问权限，则进入执行保护代码；否则此线程将在此处等待，直到信号量被释放为止
    await _serverSemaphore.WaitAsync();
    return true;
  }

   public void ConfigureServices(IServiceCollection services)
    {
      services.AddStackPolicy(options =>
      {
        //最大并发请求数
        options.MaxConcurrentRequests = 2;
        //请求队列长度限制
        options.RequestQueueLimit = 1;
      });
      services.AddControllers();
    }

 public static IServiceCollection AddStackPolicy(this IServiceCollection services, Action<QueuePolicyOptions> configure)
    {
      services.Configure(configure);
      services.AddSingleton<IQueuePolicy, StackPolicy>();
      return services;
    }

    /// <summary>
    ///   构造方法(初始化参数)
    /// </summary>
    /// <param name="options"></param>
    public StackPolicy(IOptions<QueuePolicyOptions> options)
    {
      //栈分配
      _buffer = new List<ResettableBooleanCompletionSource>();
      //队列大小
      _maxQueueCapacity = options.Value.RequestQueueLimit;
      //最大并发请求数
      _maxConcurrentRequests = options.Value.MaxConcurrentRequests;
      //剩余可用空间
      _freeServerSpots = options.Value.MaxConcurrentRequests;
    }

  public ValueTask<bool> TryEnterAsync()
    {
      lock (_bufferLock)
      {
        if (_freeServerSpots > 0)
        {
          _freeServerSpots--;
          return _trueTask;
        }
        // 如果队列满了，取消先前的请求
        if (_queueLength == _maxQueueCapacity)
        {
          _hasReachedCapacity = true;
          _buffer[_head].Complete(false);
          _queueLength--;
        }
        var tcs = _cachedResettableTCS "htmlcode">

  public void OnExit()
    {
      lock (_bufferLock)
      {
        if (_queueLength == 0)
        {
          _freeServerSpots++;

          if (_freeServerSpots > _maxConcurrentRequests)
          {
            _freeServerSpots--;
            throw new InvalidOperationException("OnExit must only be called once per successful call to TryEnterAsync");
          }

          return;
        }

        // step backwards and launch a new task
        if (_head == 0)
        {
          _head = _maxQueueCapacity - 1;
        }
        else
        {
          _head--;
        }
        //退出,出栈
        _buffer[_head].Complete(true);
        _queueLength--;
      }
    }


总结


基于栈结构的特点，在实际应用中，通常只会对栈执行以下两种操作：

  
向栈中添加元素，此过程被称为"进栈"（入栈或压栈）；
  
从栈中提取出指定元素，此过程被称为"出栈"（或弹栈）；

队列存储结构的实现有以下两种方式：

  
顺序队列：在顺序表的基础上实现的队列结构；
  
链队列：在链表的基础上实现的队列结构；

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。