从 C# 中的多个异步方法（即线程）增加值类型

Question

我需要从 C# 中的多个线程（异步方法）中增加一个计数器。

• 我无法传递 ref 参数，因为它是异步方法
• 我不能只更新值（或锁定它），因为它是一种值类型
• 我无法使用 Interlocked，因为我无法在异步方法中将 ref 指向计数器

所以我唯一想出的办法就是制作一些像List<int> 这样的傻东西，然后把我的int 放在那里，这样线程就可以锁定列表并更新值。

我希望这是一个已知的用例，并且有更优雅的方式来实现它？

这是一个小例子，不要介意小的语法问题：

public void DoStuff()
{
    int counter;
    var tasks = new List<Task>()
    for(int i = 0; i < 10; i++)
    {
        tasks.Add(AsyncMethod(<SOMETHING>));
    }
    Task.WaitAll(tasks);
    Console.WriteLine("Total: {0}", counter);
 }

 public async Task AsyncMethod(<SOMETHING>)
 {
     // Lock if needed by <SOMETHING>
     <SOMETHING>+=20;
 }

我需要创建一个带有int 字段的类，还是C# 提供了现成的东西？我并没有坚持这一点，只是想在事后学习是否有更好的方法。谢谢！

对于未来的访客： 共识似乎是创建一个自定义类，例如class IntHolder { public int Value {get;set;}}，可以通过引用传递并锁定（或使用Interlocked on）

非常感谢！

Answer 1

您可以在任何对象上使用lock，而不仅仅是您要使用的对象。

例如：

object locking_object = new object();

这将创建一个仅用于锁定的对象。

然后，当你想增加值时：

lock(locking_object)
{
    integer++;
}

根据 cmets 更新：

创建一个类来保存整数值，如下所示：

class IntHolder
{
    public int Value;
}

您可以使用Interlocked 类执行以下操作：

Interlocked.Increment(ref int_holder.Value);

其中int_holder 是您传递给方法的IntHolder 类型变量的名称。

Answer 2

如果您希望能够在异步方法之间传递值，也许您可​​以利用AsyncLocal<T>：

private AsyncLocal<int> counter = new AsyncLocal<int>();
public async Task FooAsync()
{
     await Task.Yield();
     Interlocked.Increment(ref counter.Value);
}

Answer 3

我想我会发布一个完整的代码示例 b/c 有些事情可能很棘手。

    public class MyIntIncrementer
    {
        public int MyInt = 0;
    }

    public static String TimeStamp
    {
        get { return DateTime.UtcNow.ToString("HH:mm:ss.fff"); } //yyyy-MM-dd
    }

    public static void Main(string[] args)
    {
        List<Task<string>> tasks = new List<Task<string>>();
        int waitSeconds = 5;

        Console.WriteLine(String.Format("{0}: Start", TimeStamp));
        DateTime start = DateTime.Now;

        MyIntIncrementer iIncrementer = new MyIntIncrementer();
        iIncrementer.MyInt = 0;

        for (int i = 0; i < 10; i++)
        {
            //definitely loops and changes values - but when passed in to the function they don't remain that way... see iParam
            //Console.WriteLine(String.Format("{0}: Looping... i: {1}\n", TimeStamp,i));

            tasks.Add(Task.Run(() =>
            {
                // all have 10 => last value :(
                // Console.WriteLine(String.Format("{0}: Running... i: {1}\n", TimeStamp, i));

                return SayYesIfEven(waitSeconds, i, iIncrementer);
            }));
        }

        Console.WriteLine(String.Format("{0}: Before Wait...", TimeStamp));

        // wait for them to run
        Task.WhenAll(tasks).Wait();
        //Task.WhenAll(tasks); // doesn't wait with .Wait()

        Console.WriteLine(String.Format("{0}: After Wait... Results:", TimeStamp));

        // get the results
        for (int i = 0; i < tasks.Count; i++)
        {
            Console.WriteLine(tasks[i].Result);
        }

        Console.WriteLine(String.Format("{0}: Done  ({1}s)", TimeStamp, (DateTime.Now - start).TotalSeconds));
    }

    public static async Task<string> SayYesIfEven(int waitSeconds, int iParam, MyIntIncrementer iIncrementer)
    {
        int localIParamStart = (int)iParam; // no difference from passed in value when copied locally

        int currentIStart = iIncrementer.MyInt; // not guaranteed to be unique

        // iParam is the last value and when 'iIncrementer.MyInt' prints here, it's sometimes the same in multiple threads
        Console.WriteLine(String.Format("{0:00}: Before Increment: even? {1} <=> {2:00} / iP: {3:00} / LiP: {4:00} / in.mP: {5:00}", TimeStamp, (currentIStart % 2 == 0 ? "Yes" : "No "), currentIStart, iParam, localIParamStart, iIncrementer.MyInt));

        // best way to get a unique value 
        int currentIR = Interlocked.Increment(ref iIncrementer.MyInt); // all threads wait on a lock to increment and then they move forward with their own values
        int currentI = iIncrementer.MyInt;
        int localIParam = (int)iParam;

        Console.WriteLine(String.Format("{0:00}: After  Increment: even? {1} <=> {2:00} => {6:00} => {7:00} / iP: {3:00} / LiP: {4:00} => {8:00} / in.mP: {5:00}", TimeStamp, (currentI % 2 == 0 ? "Yes" : "No "), currentIStart, iParam, localIParamStart, iIncrementer.MyInt, currentIR, currentI, localIParam));

        await Task.Delay(waitSeconds * 1000); // simulate delay

        await Task.Run(() =>
        {
            // do other stuff...

            // iParam and iIncrementer.value have the last value (note that this statement runs after the above delay)
            Console.WriteLine(String.Format("{0:00}: Inside Run after Delay: even? {1} <=> {2:00} => {6:00} => {7:00} / iP: {3:00} / LiP: {4:00} => {8:00} / in.mP: {5:00}", TimeStamp, (currentI % 2 == 0 ? "Yes" : "No "), currentIStart, iParam, localIParamStart, iIncrementer.MyInt, currentIR, currentI, localIParam));
            return "something";
        });

        // all have last value when showing what was passed into SayYesIfEven - and iIncrementer.value is also the last value
        return (String.Format("{0:00}: Returning: even? {1} <=> {2:00} => {6:00} => {7:00} / iP: {3:00} / LiP: {4:00} => {8:00} / in.mP: {5:00}", TimeStamp, (currentI % 2 == 0 ? "Yes" : "No "), currentIStart, iParam, localIParamStart, iIncrementer.MyInt, currentIR, currentI, localIParam));
    }

输出：

    13:55:35.340: Start
    13:55:35.357: Before Wait...

    // rearranged to show before/after values side by side
    // note the duplicate values for MyIntIncrementer.MyInt - and last values for iParam

    13:55:35.357: Before Increment: even? Yes <=> 00 / iP: 10 / LiP: 10 / in.mP: 00
    13:55:35.357: Before Increment: even? Yes <=> 00 / iP: 10 / LiP: 10 / in.mP: 00
    13:55:35.371: Before Increment: even? Yes <=> 02 / iP: 10 / LiP: 10 / in.mP: 02
    13:55:35.371: Before Increment: even? No  <=> 03 / iP: 10 / LiP: 10 / in.mP: 03
    13:55:35.371: Before Increment: even? Yes <=> 04 / iP: 10 / LiP: 10 / in.mP: 04
    13:55:35.371: Before Increment: even? No  <=> 05 / iP: 10 / LiP: 10 / in.mP: 05
    13:55:35.371: Before Increment: even? Yes <=> 06 / iP: 10 / LiP: 10 / in.mP: 06
    13:55:35.371: Before Increment: even? No  <=> 07 / iP: 10 / LiP: 10 / in.mP: 07
    13:55:35.371: Before Increment: even? No  <=> 07 / iP: 10 / LiP: 10 / in.mP: 07
    13:55:35.371: Before Increment: even? Yes <=> 00 / iP: 10 / LiP: 10 / in.mP: 00

    // after the locked increment, notice we have reliable independent values

    13:55:35.371: After  Increment: even? Yes <=> 00 => 02 => 02 / iP: 10 / LiP: 10 => 10 / in.mP: 02
    13:55:35.371: After  Increment: even? No  <=> 00 => 01 => 01 / iP: 10 / LiP: 10 => 10 / in.mP: 01
    13:55:35.371: After  Increment: even? No  <=> 02 => 03 => 03 / iP: 10 / LiP: 10 => 10 / in.mP: 03
    13:55:35.371: After  Increment: even? Yes <=> 03 => 04 => 04 / iP: 10 / LiP: 10 => 10 / in.mP: 04
    13:55:35.371: After  Increment: even? No  <=> 04 => 05 => 05 / iP: 10 / LiP: 10 => 10 / in.mP: 05
    13:55:35.371: After  Increment: even? Yes <=> 05 => 06 => 06 / iP: 10 / LiP: 10 => 10 / in.mP: 06
    13:55:35.371: After  Increment: even? No  <=> 06 => 07 => 07 / iP: 10 / LiP: 10 => 10 / in.mP: 07
    13:55:35.371: After  Increment: even? Yes <=> 07 => 08 => 08 / iP: 10 / LiP: 10 => 10 / in.mP: 08
    13:55:35.371: After  Increment: even? No  <=> 07 => 09 => 09 / iP: 10 / LiP: 10 => 10 / in.mP: 09
    13:55:35.371: After  Increment: even? Yes <=> 00 => 10 => 10 / iP: 10 / LiP: 10 => 10 / in.mP: 10

    13:55:40.381: Inside Run after Delay: even? Yes <=> 07 => 08 => 08 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Inside Run after Delay: even? Yes <=> 05 => 06 => 06 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Inside Run after Delay: even? No  <=> 07 => 09 => 09 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Inside Run after Delay: even? No  <=> 04 => 05 => 05 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Inside Run after Delay: even? No  <=> 02 => 03 => 03 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Inside Run after Delay: even? No  <=> 00 => 01 => 01 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Inside Run after Delay: even? Yes <=> 00 => 10 => 10 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Inside Run after Delay: even? Yes <=> 00 => 02 => 02 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Inside Run after Delay: even? Yes <=> 03 => 04 => 04 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Inside Run after Delay: even? No  <=> 06 => 07 => 07 / iP: 10 / LiP: 10 => 10 / in.mP: 10

    // notice at the bottom of the call - MyIntIncrementer.MyInt is the last value and thus never unique
    // - only the initial value (obtained after the lock and before any delay) is still reliable - same behavior found on a 100+ loop

    13:55:40.381: After Wait... Results:

    13:55:40.381: Returning: even? Yes <=> 00 => 10 => 10 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Returning: even? No  <=> 00 => 01 => 01 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Returning: even? Yes <=> 00 => 02 => 02 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Returning: even? No  <=> 02 => 03 => 03 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Returning: even? Yes <=> 03 => 04 => 04 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Returning: even? No  <=> 04 => 05 => 05 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Returning: even? Yes <=> 05 => 06 => 06 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Returning: even? No  <=> 06 => 07 => 07 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Returning: even? Yes <=> 07 => 08 => 08 / iP: 10 / LiP: 10 => 10 / in.mP: 10
    13:55:40.381: Returning: even? No  <=> 07 => 09 => 09 / iP: 10 / LiP: 10 => 10 / in.mP: 10

    13:55:40.381: Done  (5.0410934s)