如何将参数传递给排队的后台任务（.net 核心）

Question

在我的 Web 应用程序中，我有一个长运行任务，我想在后台调用这个任务。因此，根据文档 .net core 3.1 Queued background tasks 我为此使用了这样的代码：

public interface IBackgroundTaskQueue
{
    ValueTask QueueBackgroundWorkItemAsync(Func<CancellationToken, ValueTask> workItem);

    ValueTask<Func<CancellationToken, ValueTask>> DequeueAsync(CancellationToken cancellationToken);
}

public class BackgroundTaskQueue : IBackgroundTaskQueue
{
    private readonly Channel<Func<CancellationToken, ValueTask>> _queue;

    public BackgroundTaskQueue(int capacity)
    {
        var options = new BoundedChannelOptions(capacity){FullMode = BoundedChannelFullMode.Wait};
        _queue = Channel.CreateBounded<Func<CancellationToken, ValueTask>>(options);
    }

    public async ValueTask QueueBackgroundWorkItemAsync(Func<CancellationToken, ValueTask> workItem)
    {
        if (workItem == null)throw new ArgumentNullException(nameof(workItem));
        await _queue.Writer.WriteAsync(workItem);
    }

    public async ValueTask<Func<CancellationToken, ValueTask>> DequeueAsync(CancellationToken cancellationToken)
    {
        var workItem = await _queue.Reader.ReadAsync(cancellationToken);
        return workItem;
    }
}

和托管服务

public class QueuedHostedService : BackgroundService
{
    private readonly ILogger<QueuedHostedService> _logger;

    public QueuedHostedService(IBackgroundTaskQueue taskQueue, ILogger<QueuedHostedService> logger)
    {
        TaskQueue = taskQueue;
        _logger = logger;
    }

    public IBackgroundTaskQueue TaskQueue { get; }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        await BackgroundProcessing(stoppingToken);
    }

    private async Task BackgroundProcessing(CancellationToken stoppingToken)
    {
        while (!stoppingToken.IsCancellationRequested)
        {
            var workItem = await TaskQueue.DequeueAsync(stoppingToken);

            try
            {
                await workItem(stoppingToken);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Error occurred executing {WorkItem}.", nameof(workItem));
            }
        }
    }

    public override async Task StopAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("Queued Hosted Service is stopping.");
        await base.StopAsync(stoppingToken);
    }
}

然后我注册所有服务

services.AddHostedService<QueuedHostedService>();
services.AddSingleton<IBackgroundTaskQueue>(new BackgroundTaskQueue(queueCapacity));

然后我可以像在这样的示例中那样通过不带参数的调用成功使用它

public async Task<TenantBo> RegisterCompanyAsync(AddTenantBo addTenantBo)
{
  var tenantBo = new TenantBo();

  try
  {
    _companyRegistrationLogHelper.SetInfoLog(GetTenantId(tenantBo), 
      "Start create company: " + JsonConvert.SerializeObject(addTenantBo));

      InitOnCreateCompanyTasks(tenantBo);

      //skip if already create tenant 
      tenantBo = await CreateTenantAsync(tenantBo, addTenantBo);

      //run in background
      _companyRegistationQueue.QueueBackgroundWorkItemAsync(RunRegistrationCompanyMainAsync);

      return tenantBo;
  }
  catch (Exception e)
  {
    //some logs
    return tenantBo;
  }
}

private async ValueTask RunRegistrationCompanyMainAsync(CancellationToken cancellationToken)
{
  //some await Tasks
}

private async ValueTask RunRegistrationCompanyMainAsync(string tenantId, CancellationToken cancellationToken)
{
  //some await Tasks
}

所以我只能用一个参数调用 RunRegistrationCompanyMainAsync(CancellationToken cancellationToken) 而不能用两个参数调用 RunRegistrationCompanyMainAsync(string tenantId, CancellationToken cancellationToken)

你能帮我传递字符串参数作为这个任务的参数吗？

Answer 1

在QueueBackgroundWorkItemAsync(RunRegistrationCompanyMainAsync)调用编译器实际执行cast from method group into a delegate. But to provide instance of Func delegate your are not limited to method groups, you can provide a lambda expression例如：

 var someTenantId = ....
 .....
_companyRegistationQueue.QueueBackgroundWorkItemAsync(ct => RunRegistrationCompanyMainAsync(someTenantId, ct));

Answer 2

过了一段时间我找到了解决办法。只需要像这样使用元组

public class CompanyRegistationQueue : ICompanyRegistationQueue
    {
        private readonly Channel<Tuple<CreateCompanyModel, Func<CreateCompanyModel, CancellationToken, ValueTask>>> _queue;

        public CompanyRegistationQueue(int capacity)
        {
            var options = new BoundedChannelOptions(capacity) { FullMode = BoundedChannelFullMode.Wait };
            _queue = Channel.CreateBounded<Tuple<CreateCompanyModel, Func<CreateCompanyModel, CancellationToken, ValueTask>>**>(options);
        }

        public async ValueTask QueueBackgroundWorkItemAsync(Tuple<CreateCompanyModel, Func<CreateCompanyModel, CancellationToken, ValueTask>> workItem)
        {
            if (workItem == null) throw new ArgumentNullException(nameof(workItem));
            await _queue.Writer.WriteAsync(workItem);
        }

        public async ValueTask<Tuple<CreateCompanyModel, Func<CreateCompanyModel, CancellationToken, ValueTask>>> DequeueAsync(CancellationToken cancellationToken)
        {
            var workItem = await _queue.Reader.ReadAsync(cancellationToken);
            return workItem;
        }
    }

然后这样称呼它

private async Task BackgroundProcessing(CancellationToken stoppingToken)
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                var workItem = await TaskQueue.DequeueAsync(stoppingToken);

                try
                {
//item2 is task
                    await workItem.Item2(workItem.Item1, stoppingToken);
                }
                catch (Exception ex)
                {
                    _logger.LogError(ex, "Error occurred executing {WorkItem}.", nameof(workItem));
                }
            }
        }

在代码中调用

var paramValue = new Tuple<CreateCompanyModel, Func<CreateCompanyModel, CancellationToken, ValueTask>>(createCompanyModel, RunRegistrationCompanyMainAsync);
                await _companyRegistationQueue.QueueBackgroundWorkItemAsync(paramValue);

P.S。 May by Tuple 不是最好的解决方案，而是它的工作

如何将参数传递给排队的后台任务（.net 核心）

How can I pass parameters to queued background task (.net core)

.net

.net-core

background-process

self-hosting