WaitUntil直到IF Cond

如何解决WaitUntil直到IF Cond

我正在使用并行Foreach。我也在foreach中称为webapi。我想控制来自api的响应。如果我获得了真值或某种价值，我想完成所有任务并进行每次迭代。

我在stackoverflow中进行搜索，但看不到任何响应。

Task<bool>[] tasks = new Task<bool>[customers.Count()];
CancellationTokenSource tokenSource = new CancellationTokenSource();
CancellationToken token = tokenSource.Token;
ParallelOptions po = new ParallelOptions();
po.MaxDegreeOfParallelism = System.Environment.ProcessorCount;

Parallel.ForEach(customers,po,async (customer,state,index) =>
{
    po.CancellationToken.ThrowIfCancellationRequested();
    var filePath = Path.Combine(_hostingEnvironment.WebrootPath,"Photos",$"{customer.CustomerNumber}.jpg");
    byte[] secondImageBytes = await System.IO.File.ReadAllBytesAsync(filePath).ConfigureAwait(false);
    ByteArrayContent secondImage = new ByteArrayContent(secondImageBytes);

    var test = await SomeFunction().ConfigureAwait(false);
    if (test)
    {
        //cancel all foreach task
    }
});

为了理解，请测试代码：

  static async Task Main(string[] args)
    {
        Stopwatch watch = new Stopwatch();
        watch.Start();
        List<TaskItem> taskList = new();
        taskList.Add(new TaskItem { Id = 1,Delay = 100,isOkey = true,Name = "Try 1" });
        taskList.Add(new TaskItem { Id = 2,Delay = 2000,isOkey = false,Name = "Try 2" });
        taskList.Add(new TaskItem { Id = 3,Name = "Try 3" });
        taskList.Add(new TaskItem { Id = 4,Name = "Try 4" });
        taskList.Add(new TaskItem { Id = 5,Name = "Try 5" });
        taskList.Add(new TaskItem { Id = 6,Delay = 200,Name = "Try 6" });
        taskList.Add(new TaskItem { Id = 7,Delay = 10000,Name = "Try 7" });
        taskList.Add(new TaskItem { Id = 8,Name = "Try 8" });
        taskList.Add(new TaskItem { Id = 9,Name = "Try 9" });
        var control=await TestTask2Async(taskList);
        Console.WriteLine("Result ="+control);
        watch.Stop();
        Console.WriteLine(watch.Elapsed.TotalSeconds.ToString());
        Console.ReadKey();
    }
    public static async Task<int> TestTaskAsync(List<TaskItem> taskList)
    {       
        var matchedId = 0;       
        try
        {
            var tokenSource = new CancellationTokenSource();
            var token = tokenSource.Token;
            var SoMetask = Task.Factory.StartNew(async () =>
            {               
                await Task.WhenAll(taskList.AsEnumerable().Select(async item =>
                {
                    token.ThrowIfCancellationRequested();
                    await Task.Delay(100);
                    await Task.Delay(1000);
                    await Task.Delay(item.Delay);                        
                    Console.WriteLine("Process for " + item.Id);
                    if (item.isOkey)
                    {
                        Console.WriteLine("Founded " + item.Id);
                        matchedId = item.Id;                            
                        tokenSource.Cancel();                            
                    }
                }));
            },token);
            await SoMetask.Result;
        }
        catch (Exception e)
        {
            Console.WriteLine(e.Message);
        }
        return matchedId;
    }


    public static async Task<int> TestTask2Async(List<TaskItem> taskList)
    {
        var matchedId = 0;
        try
        {
            var tokenSource = new CancellationTokenSource();
            var token = tokenSource.Token;
            
            await Task.WhenAll(taskList.AsEnumerable().Select(async item =>
            {
                token.ThrowIfCancellationRequested();
                await Task.Delay(100).ConfigureAwait(false); 
                await Task.Delay(1000).ConfigureAwait(false); 
                await Task.Delay(item.Delay).ConfigureAwait(false); 
                Console.WriteLine("Process for " + item.Id);
                if (item.isOkey)
                {
                    Console.WriteLine("Founded " + item.Id);
                    matchedId = item.Id;
                    tokenSource.Cancel();
                }
            }));
        }
        catch (Exception)
        {
        }
        return matchedId;
    }
  public class TaskItem
{
    public int Id { get; set; }
    public int Delay { get; set; }
    public string Name { get; set; }
    public bool isOkey { get; set; }
}

• 结果：

  处理4

  5次处理

  处理1

  3次处理

  成立1

  6次处理

  处理2

  处理7

  处理9

  处理8

  结果= 1

  11.2402357

但是我想如果Found（bla）建立了，所有的任务都会死掉，我不想在Found建立后看到（bla）的过程。

在这个例子中，我只想看看：

处理4

5次处理

处理1

3次处理

成立1

结果= 1

1.2402357

解决方法

Parallel.ForEach不适用于async-await。

所有项目都到达第一个未完成的Parallel.ForEach时，await将终止。

尝试以下方法：

var tokenSource = new CancellationTokenSource();
var token = tokenSource.Token;

await Task.WhenAll(customers.Select(async customer =>
{
    token.ThrowIfCancellationRequested();
    var filePath = Path.Combine(_hostingEnvironment.WebRootPath,"Photos",$"{customer.CustomerNumber}.jpg");
    var secondImageBytes = await File.ReadAllBytesAsync(filePath).ConfigureAwait(false);
    var secondImage = new ByteArrayContent(secondImageBytes);

    var test = await SomeFunction().ConfigureAwait(false);
    if (test)
    {
        tokenSource.Cancel();
    }
}));

此外，请勿将Task.Factory.StartNew-async与await一起使用。请改用Task.Run。

关于取消标记，您需要了解的一件事是它表明了取消的意图，但它本身并不能取消任何东西。该代码需要对其进行检查并以所需的任何方式取消。

尝试一下：

public static async Task<int> TestTask2Async(List<TaskItem> taskList)
{
    var matchedId = 0;
    try
    {
        var tokenSource = new CancellationTokenSource();
        var token = tokenSource.Token;

        await Task.WhenAll(taskList.AsEnumerable().Select(async item =>
        {
            token.ThrowIfCancellationRequested();
            // add token to the call to Task.Delay
            await Task.Delay(100,token).ConfigureAwait(false);
            await Task.Delay(1000,token).ConfigureAwait(false);
            await Task.Delay(item.Delay,token).ConfigureAwait(false);
            // check it again
            token.ThrowIfCancellationRequested();
            Console.WriteLine("Process for " + item.Id);
            if (item.isOkey)
            {
                // cancel as soon as the condition has been met
                tokenSource.Cancel();
                Console.WriteLine("Founded " + item.Id);
                matchedId = item.Id;
            }
        }));
    }
    catch (Exception ex)
    {
    }
    return matchedId;
}