我应该将一个任务包装在另一个任务中还是应该只返回创建的任务？ [英] Should I wrap a task in another task or should I just return the created task?

问题描述

我正在构建一个使用ADO.NET的.NET 4.0应用程序，因此我无法使用async / await。
我不想要一个解决方案，但是我想知道以下哪种实现是最佳的，为什么。我的单元测试通过了所有三个实现，但是我想知道这三个实现之间的区别。

I'm building a .NET 4.0 application that uses ADO.NET, so I cannot use async/await. I don't want a solution for that, but I do want to know what of the following implementations is best and why. My unit tests pass for all three implementations, but I want to know the difference between these three.

在第一个实现中，我将一个任务包装在另一个任务中。我认为将两项任务分开对性能不利，但我不确定。

In my first implementation I wrap a task in another task. I think spinning up two tasks is bad for performance, but I'm not sure.

public virtual Task<IDataReader> ExecuteReaderAsync(IDbCommand dbCommand, CancellationToken cancellationToken)
{
    return Task.Factory.StartNew(() =>
    {
        var sqlCommand = CheckIfSqlCommand(dbCommand);
        PrepareExecuteReader(dbCommand);

        return Task<IDataReader>
            .Factory
            .FromAsync(sqlCommand.BeginExecuteReader, sqlCommand.EndExecuteReader, null)
            .Result;
    }, cancellationToken);
}

＃2使用TaskCompletionSource

然后我尝试将结果包装在 TaskCompletionSource 中，这样我只有一个任务。

#2 Using TaskCompletionSource

Then I tried wrapping the result in a TaskCompletionSource so I just have one task.

public virtual Task<IDataReader> ExecuteReaderAsync(IDbCommand dbCommand, CancellationToken cancellationToken)
{
    var taskCompletionSource = new TaskCompletionSource<IDataReader>();
    var sqlCommand = CheckIfSqlCommand(dbCommand);
    PrepareExecuteReader(dbCommand);

    var reader = Task<IDataReader>
        .Factory
        .FromAsync(sqlCommand.BeginExecuteReader, sqlCommand.EndExecuteReader, null)
        .Result;

    taskCompletionSource.SetResult(reader);

    return taskCompletionSource.Task;
}

＃3直接返回Task

我的最终解决方案是直接返回我创建的任务，而不是包装它。

#3 returning Task directly

My final solution is to directly return the task I created instead of wrapping it.

public virtual Task<IDataReader> ExecuteReaderAsync(IDbCommand dbCommand, CancellationToken cancellationToken)
{
    var sqlCommand = CheckIfSqlCommand(dbCommand);
    PrepareExecuteReader(dbCommand);

    return Task<IDataReader>
        .Factory
        .FromAsync(sqlCommand.BeginExecuteReader, sqlCommand.EndExecuteReader, null);
}

所以基本上我的问题是：

我应该使用什么选项，或者有更好的方法呢？

So basically my question is:

What option should I use or is there a better way to do this?

推荐答案

您的＃3是最好。前两个无故引入了并发症。

Your #3 is the best. The first two introduce complication for no reason.

1可能纯粹添加另一个线程来运行 CheckIfSqlCommand（）和 PrepareExecuteReader（）异步。这可能就是您想要的，但是它们听起来并不像要花费很长时间的命令。

1 potentially adds another thread purely to run CheckIfSqlCommand() and PrepareExecuteReader() asynchronously. This may be what you wanted, but they don't sound like commands that are going to take a long time.

2个引用 .Result 的任务，该任务将一直阻塞到任务完成为止，因此无法实现使用任务的全部目的。

2 references .Result of the task, which will block until the task is complete, so defeats the whole purpose of using tasks.

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