WaitUntil IF Cond
WaitUntil IF Cond
提问于 2020-11-05 10:46:58
我在用paralel Foreach。同时，我在前额调用了webapi。我想控制api的响应。如果我得到了真或某物的价值，我想完成所有的任务，并提前迭代。
我搜索堆叠溢出，但我看不到任何反应。
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，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, Delay = 100, isOkey = false, Name = "Try 3" });
taskList.Add(new TaskItem { Id = 4, Delay = 100, isOkey = false, Name = "Try 4" });
taskList.Add(new TaskItem { Id = 5, Delay = 100, isOkey = false, Name = "Try 5" });
taskList.Add(new TaskItem { Id = 6, Delay = 200, isOkey = false , Name = "Try 6" });
taskList.Add(new TaskItem { Id = 7, Delay = 10000, isOkey = false, Name = "Try 7" });
taskList.Add(new TaskItem { Id = 8, Delay = 10000, isOkey = false, Name = "Try 8" });
taskList.Add(new TaskItem { Id = 9, Delay = 10000, isOkey = false, 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：
4种工艺
5种工艺
工艺1
3种工艺
成立1
6种工艺
工艺2
过程7
进程9
过程8
结果=1
11.2402357
但是我想如果成立(bla)，所有的任务都将是死亡，我不想看到(bla)在创建后的过程。
对于这个例子，我只想看到：
4种工艺
5种工艺
工艺1
3种工艺
成立1
结果=1
1.2402357
回答 1
Stack Overflow用户
发布于 2020-11-05 18:52:32
Parallel.ForEach的设计并不是为了与async-await一起工作.
一旦到达所有项目的第一个未完成的Parallel.ForEach，该await就会终止。
试一试：
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();
}
}));另外，不要将Task.Factory.StartNew与async-await结合使用。使用Task.Run代替。
关于取消令牌，您需要知道的一件事是，它表明了取消的意图，但它本身并没有取消任何东西。代码需要检查它并以任何需要的方式取消它。
试试这个：
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;
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/64695602
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