如何从 Task.WhenAll 执行返回未取消的任务

Question

我有一个可取消的任务列表； 他们有他们的CancellationTokenSource 。 他们的取消独立于其他人。 我想从Task.WhenAll返回所有未取消的任务。

var tasks = new List<Task<string>>();

/** some code here **/

var done = await Task.WhenAll(tasks); // This throws an OperationCanceledException,
                                      // when at least one task is cancelled.

StackOverflow 中有“如何取消任务内的任务”的问题，但这里的问题并非如此。

Answer 1

您可以通过循环Task.WhenAll重试其余的任务

var tasks = new List<Task<string>>();

/** some code here **/
var notCanceled = tasks;
do
{
    try
    {
        await Task.WhenAll(notCanceled);
        break;
    }
    catch (OperationCanceledException)
    {
        notCanceled = notCanceled.Where(t => !t.IsCanceled).ToArray();
    }
} while (notCanceled.Any())

Answer 2

一种方法是将Task.WhenAll任务存储在Task变量中，以便您可以添加专门处理IsCanceled情况的catch块。

var tasks = new List<Task<string>>();

/** some code here **/

Task whenAll = Task.WhenAll(tasks);
Task<string>[] successfullyCompletedTasks;

try
{
    await whenAll;
    successfullyCompletedTasks = tasks.ToArray();
}
catch when (whenAll.IsCanceled)
{
    successfullyCompletedTasks = tasks.Where(t => !t.IsCanceled).ToArray();
}

// Make sure that our assumptions do not contradict the reality
Debug.Assert(successfullyCompletedTasks.All(t => t.IsCompletedSuccessfully));