Question

如何在Parallel.Foreach中定义计数器并且停止以特定数量拍摄？
我问了这个问题，因为Parallel.ForEach中的那个计数器在常规操作中不起作用请看这个小例子：

static void Main(string[] args)
{
    int Count_Step = -1;
    string[] lines = new string[] 
    { 
        "0",
        "1",
        "2",
        "3",
        "4",
        "5",
        "6",
        "7",
        "8",
        "9",
        "10",
        "11",
        "12",
        "13",
        "14",
        "15",
        "16",
        "17",
        "18",
        "19"
    };

    List<string> list_lines = new List<string>(lines);

    ParallelOptions parallelOptions = new ParallelOptions();
    parallelOptions.MaxDegreeOfParallelism = 3;

    Parallel.ForEach(list_lines, parallelOptions, (line, state, index) =>
    {
        if (Count_Step == 10)
            state.Stop();
        Count_Step++;
        Console.WriteLine(index + " : " + line + " : " + Count_Step);
        //Thread.Sleep(5000);
    });

    Console.ReadLine();
}

我想输出10行，而不是更多！我怎么能这样做？

提前致谢

Answer 1

如果您只想输出10行，请改为

static void Main(string[] args)
{
    var lines = new List<string> 
    { 
        "0",
        "1",
        "2",
        "3",
        "4",
        "5",
        "6",
        "7",
        "8",
        "9",
        ...
    };

    var parallelOptions = new ParallelOptions
        {        
            MaxDegreeOfParallelism = 3
        };

    Parallel.ForEach(lines.Take(10), parallelOptions, (line, index) =>
    {
        Console.WriteLine("{0} : {1}", index, line);
        ////Thread.Sleep(5000);
    });

    Console.ReadLine();
}

替代地

static void Main(string[] args)
{
    var lines = new List<string> 
    { 
        "0",
        "1",
        "2",
        "3",
        "4",
        "5",
        "6",
        "7",
        "8",
        "9",
        ...
    };

    var parallelOptions = new ParallelOptions
        {        
            MaxDegreeOfParallelism = 3
        };

    Parallel.For(0, 9, parallelOptions, i =>
    {
        Console.WriteLine("{0} : {1}", i, lines[i]);
        ////Thread.Sleep(5000);
    });

    Console.ReadLine();
}

甚至

static void Main(string[] args)
{
    var lines = new List<string> 
    { 
        "0",
        "1",
        "2",
        "3",
        "4",
        "5",
        "6",
        "7",
        "8",
        "9",
        ...
    };

    Enumerable.Range(0, 10).AsParallel().WithDegreeOfParallelism(3).ForAll(i =>
    {
        Console.WriteLine("{0} : {1}", i, lines[i]);
        ////Thread.Sleep(5000);
    }

    Console.ReadLine();
}

如果您真的希望并行迭代更新循环外的某些值，那么您需要确保更改变量的所有更新和读取都是线程安全的。

如果要递增整数，可以这样做。

var stepCount = 0;

Enumerable.Range(0, 10).AsParallel().WithDegreeOfParallelism(3).ForAll(i =>
    {
        var thisCount = Interlocked.Increment(ref stepCount);
        Console.WriteLine("{0} : {1} : {2}", i, lines[i], thisCount);
        ////Thread.Sleep(5000);
    }

Console.ReadLine();

但是，thisCount的输出在控制台窗口中并不是连续的，在两行之间可能会有一个线程切换。

如果你想做更复杂的事情，比如取消处理，你应该看一下BlockingCollection。

Answer 2

尝试Parallel.For()

Parallel.For Method

如何在Parallel.Foreach中定义计数器并在特定数量中停止该循环

2 个答案: