按完成时间排序任务,同时在参数列表中跟踪其索引? [英] Ordering Tasks by completion time while keeping track of their index in an argument list?
问题描述
I recently asked a question about the possibility of cleaning up some code, the code was meant to wait for each Task
in a List<Task<T>>
to complete but cancelling all Task
if one returned some falsey value.
名为Servy的用户迅速生成了一种方法,雄辩地在完成时间之前订购了List<Task<T>>
.阅读答案后,我认为/认为我理解/理解了该方法.然后,我去使用该方法,但很快意识到了一个问题.我需要能够在Task
完成时识别它们.但是Servy建议的Order
方法没有提供执行此操作的方法(因为我无法将Order
返回的任务继续与我最初提供的List<Task<>>
进行比较).
A user named Servy quickly produced a method which eloquently orders a List<Task<T>>
by their completion time. After reading over the answer a bit I think/thought I understand/stood the method. I then went to use the method but quickly realized an issue. I need to be able to recognize the Task
s as they are completing. But the Order
method Servy suggested provides no means to do this (because I cannot compare the task continuations returned by Order
to my List<Task<>>
I supplied it originally).
因此,我去更改了方法以返回Tuple<T, int>
,其中int
表示提供的参数中Task
的原始索引.
So I went to change the method to return a Tuple<T, int>
where the int
represents the original index of the Task
in the provided arguments.
public static IEnumerable<Task<Tuple<T, int>>> OrderByCompletion<T>(IEnumerable<Task<T>> tasks)
{
var taskList = tasks.ToList();
var taskSources = new BlockingCollection<TaskCompletionSource<Tuple<T, int>>>();
var taskSourceList = new List<TaskCompletionSource<Tuple<T, int>>>(taskList.Count);
for (int i = 0; i < taskList.Count; i++)
{
var task = taskList[i];
var newSource = new TaskCompletionSource<Tuple<T, int>>();
taskSources.Add(newSource);
taskSourceList.Add(newSource);
task.ContinueWith(t =>
{
var source = taskSources.Take();
if (t.IsCanceled)
source.TrySetCanceled();
else if (t.IsFaulted)
source.TrySetException(t.Exception.InnerExceptions);
else if (t.IsCompleted)
source.TrySetResult(new Tuple<T, int>(t.Result, i));
}, CancellationToken.None, TaskContinuationOptions.PreferFairness, TaskScheduler.Default);
}
return taskSourceList.Select(tcs => tcs.Task);
}
// Usage
foreach(var task in myTaskList.OrderByCompletion())
Tuple<Boolean, int> result = await task;
我面临的问题是,无论返回的任务顺序如何,返回的Tuple
内部的索引似乎总是等于传递给OrderByCompletion
的原始List<Task<>>
的Count
.
The issue I am facing is that index inside of the Tuple
returned seems to always be equal to the Count
of the original List<Task<>>
passed to OrderByCompletion
no matter the order of the task returned.
我认为,由于这个问题,我似乎并不完全了解此方法的工作原理,尽管似乎应该可以正常工作.
I assume that as a result of this issue I do not fully understand how this method worked in the first place, though it seems to be that it should work just fine.
任何人都可以解释该问题并提供解决方案吗?
推荐答案
之所以会发生这种情况,是因为您在Action<>
中使用了i
变量.
This happens because you are using i
variable inside an Action<>
.
但是创建Action
时不会执行此操作的代码,但是当任务完成时,变量i
的值为taskList.Count
(for
循环完成时).
But the code of this action is not executed when your create the Action
, but when the task is completed, then the variable i
has value taskList.Count
(when for
loop finished).
您只需将一个额外的变量添加到for
即可解决您的问题:
You can fix your problem simply adding an extra variable to the for
:
for (int i = 0; i < taskList.Count; i++)
{
var task = taskList[i];
var newSource = new TaskCompletionSource<Tuple<T, int>>();
taskSources.Add(newSource);
taskSourceList.Add(newSource);
int index = i; // <- add this variable.
task.ContinueWith(t =>
{
var source = taskSources.Take();
if (t.IsCanceled)
source.TrySetCanceled();
else if (t.IsFaulted)
source.TrySetException(t.Exception.InnerExceptions);
else if (t.IsCompleted)
source.TrySetResult(new Tuple<T, int>(t.Result, index));
}, CancellationToken.None, TaskContinuationOptions.PreferFairness, TaskScheduler.Default);
}
您可以阅读此问题/答案以了解更多详细信息.
You can read this question/answers for more details.
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