Question

在抛出OperationCancelledException之前，代码始终等待当前正在运行的任务完成。

我希望程序在条件成立时立即停止。

static void Main()
{
    // want to break out of a Parallel.For immediately when a condition occurs
    var cts = new CancellationTokenSource();
    var po = new ParallelOptions();
    po.CancellationToken = cts.Token;

    long counterTotal = 0;

    try
    {
        // want to have a sum of counts at the end
        Parallel.For<long>(1, 26, po, () => 0, delegate(int i, ParallelLoopState state, long counterSubtotal)
                {
                    po.CancellationToken.ThrowIfCancellationRequested();
                    Console.WriteLine(i.ToString());

                    for (int k = 0; k < 1000000000; k++)
                    {
                        counterSubtotal++;

                        if (i == 4 && k == 900000000)
                        {
                            cts.Cancel();
                            // Would like to break out here immediately
                        }
                    }

                    return counterSubtotal;
                }, (x) => Interlocked.Add(ref counterTotal, x)
            );
    }
    catch (OperationCanceledException e)
    {
        Console.WriteLine("Cancelled");
        Console.WriteLine("Total iterations across all threads {0}", String.Format("{0:n0}", counterTotal));
        Console.ReadLine();
    }
}

我发现在cts.Cancel()上放置一个断点，并在捕获中演示了正在发生的事情。

也看了state.Stop。

这是其他代码的简化版本。

如果我们想立即爆发，那么Parallel.For对于在方法内部长时间运行的事情来说可能并不理想。

UPDATE2： 代码现在按预期工作，并提供了良好的总数

static void Main()
{
    // want to break out of a Parallel.For immediately when a condition occurs
    var cts = new CancellationTokenSource();
    var po = new ParallelOptions();
    po.CancellationToken = cts.Token;

    long counterTotal = 0;

    try
    {
        // want to have a sum of counts at the end
        // using type param here to make counterSubtotal a long
        Parallel.For<long>(1, 26, po, () => 0, delegate(int i, ParallelLoopState state, long counterSubtotal)
                {
                    Console.WriteLine(i.ToString());
                    // 1 billion
                    for (int k = 0; k < 1000000000; k++)
                    {
                        //po.CancellationToken.ThrowIfCancellationRequested();
                        if (po.CancellationToken.IsCancellationRequested)
                        {
                            return counterSubtotal;
                        }
                        counterSubtotal++;

                        if (i == 4 && k == 400000000)
                        {
                            Console.WriteLine("Inner Cancelled");
                            cts.Cancel();
                        }
                    }
                    return counterSubtotal;
                }, (x) => Interlocked.Add(ref counterTotal, x)
            );
    }
    catch (OperationCanceledException e)
    {
        Console.WriteLine("Cancelled");
        Console.WriteLine("Total iterations across all threads {0}", String.Format("{0:n0}", counterTotal));
        Console.ReadLine();
    }
}

Answer 1

如果你想让它“立即”打破，你需要检查你内心的取消令牌。就像现在一样，它会在进入之前检查取消，但在此之后它将不会再次查看令牌。

for (int k = 0; k < 1000000000; k++)
{
    po.CancellationToken.ThrowIfCancellationRequested();
    counterSubtotal++;

    if (i == 4 && k == 900000000)
    {
       cts.Cancel();

    }
}

Parallel如果满足条件，则不立即取消所有线程

1 个答案: