从线程返回值？

时间：2009-08-21 20:49:44

标签： c# .net multithreading

如何从线程中返回值？

19 个答案:

答案 0 :(得分：83)

从线程获取返回值的最简单方法之一是使用闭包。创建一个变量，该变量将保存线程的返回值，然后在lambda表达式中捕获它。从工作线程为此变量分配“return”值，然后一旦该线程结束，您就可以从父线程中使用它。

void Main()
{
  object value = null; // Used to store the return value
  var thread = new Thread(
    () =>
    {
      value = "Hello World"; // Publish the return value
    });
  thread.Start();
  thread.Join();
  Console.WriteLine(value); // Use the return value here
}

答案 1 :(得分：32)

我会使用BackgroundWorker方法并将结果返回到e.Result。

编辑：

这通常与WinForms和WPF相关联，但可以由任何类型的.NET应用程序使用。以下是使用BackgroundWorker的控制台应用程序的示例代码：

using System;
using System.Threading;
using System.ComponentModel;
using System.Collections.Generic;
using System.Text;

namespace BGWorker
{
    class Program
    {
        static bool done = false;

        static void Main(string[] args)
        {
            BackgroundWorker bg = new BackgroundWorker();
            bg.DoWork += new DoWorkEventHandler(bg_DoWork);
            bg.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bg_RunWorkerCompleted);
            bg.RunWorkerAsync();

            while (!done)
            {
                Console.WriteLine("Waiting in Main, tid " + Thread.CurrentThread.ManagedThreadId);
                Thread.Sleep(100);
            }
        }

        static void bg_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            Console.WriteLine("Completed, tid " + Thread.CurrentThread.ManagedThreadId);
            done = true;
        }

        static void bg_DoWork(object sender, DoWorkEventArgs e)
        {
            for (int i = 1; i <= 5; i++)
            {
                Console.WriteLine("Work Line: " + i + ", tid " + Thread.CurrentThread.ManagedThreadId);
                Thread.Sleep(500);
            }
        }
    }
}

输出：

Waiting in Main, tid 10
Work Line: 1, tid 6
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Work Line: 2, tid 6
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Work Line: 3, tid 6
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Work Line: 4, tid 6
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Work Line: 5, tid 6
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Waiting in Main, tid 10
Completed, tid 6

2014年更新

请参阅@ Roger的答案。

https://stackoverflow.com/a/24916747/141172

他指出您可以使用返回Task<T>的任务，并检查Task<T>.Result。

答案 2 :(得分：26)

这取决于您希望如何创建线程和可用的.NET版本：

.NET 2.0 +：

A）您可以直接创建Thread对象。在这种情况下，您可以使用＆＃34; closure＆＃34; - 声明变量并使用lambda-expression捕获它：

object result = null;
Thread thread = new System.Threading.Thread(() => { 
    //Some work...
    result = 42; });
thread.Start();
thread.Join();
Console.WriteLine(result);

B）您可以使用委托和IAsyncResult并从EndInvoke()方法返回值：

delegate object MyFunc();
...
MyFunc x = new MyFunc(() => { 
    //Some work...
    return 42; });
IAsyncResult asyncResult = x.BeginInvoke(null, null);
object result = x.EndInvoke(asyncResult);

C）您可以使用BackgroundWorker课程。在这种情况下，您可以使用捕获的变量（与Thread对象一样）或处理RunWorkerCompleted事件：

BackgroundWorker worker = new BackgroundWorker();
worker.DoWork += (s, e) => {
    //Some work...
    e.Result = 42;
};
worker.RunWorkerCompleted += (s, e) => {
    //e.Result "returned" from thread
    Console.WriteLine(e.Result);
};
worker.RunWorkerAsync();

.NET 4.0 +：

从.NET 4.0开始，您可以使用Task Parallel Library和Task类来启动线程。通用类Task<TResult>允许您从Result属性获取返回值：

//Main thread will be blocked until task thread finishes
//(because of obtaining the value of the Result property)
int result = Task.Factory.StartNew(() => {
    //Some work...
    return 42;}).Result;

.NET 4.5 +：

从.NET 4.5开始，您还可以使用async / await关键字直接从任务返回值，而不是获取Result属性：

int result = await Task.Run(() => {
    //Some work...
    return 42; });

注意：包含上述代码的方法应标有async关键字。

由于许多原因，使用任务并行库是使用线程的首选方法。

答案 3 :(得分：21)

线程不是方法 - 您通常不会“返回”某个值。

但是，如果您尝试从某些处理的结果中取回一个值，那么您有很多选项，其中两个主要选项是：

  • 您可以同步共享的数据，并进行适当的设置。
  • 您也可以通过某种形式的回调传回数据。

这实际上取决于您创建线程的方式，以及您希望如何使用它，以及您正在使用的语言/框架/工具。

答案 4 :(得分：14)

这是一个使用委托的简单示例...... 

void Main()
{
   DoIt d1 = Doer.DoThatThang;
   DoIt d2 = Doer.DoThatThang;

   IAsyncResult r1 = d1.BeginInvoke( 5, null, null );
   IAsyncResult r2 = d2.BeginInvoke( 10, null, null );

   Thread.Sleep( 1000 );

   var s1 = d1.EndInvoke( r1 );
   var s2 = d2.EndInvoke( r2 );

   s1.Dump(); // You told me 5
   s2.Dump(); // You told me 10
}

public delegate string DoIt( int x );

public class Doer
{
  public static string DoThatThang( int x  )
  {
    return "You told me " + x.ToString();
  }
}

在Threading in C#处有一个关于线程的精彩系列。

答案 5 :(得分：12)

我最喜欢的类，只用2行代码在另一个线程上运行任何方法。

class ThreadedExecuter<T> where T : class
{
    public delegate void CallBackDelegate(T returnValue);
    public delegate T MethodDelegate();
    private CallBackDelegate callback;
    private MethodDelegate method;

    private Thread t;

    public ThreadedExecuter(MethodDelegate method, CallBackDelegate callback)
    {
        this.method = method;
        this.callback = callback;
        t = new Thread(this.Process);
    }
    public void Start()
    {
        t.Start();
    }
    public void Abort()
    {
        t.Abort();
        callback(null); //can be left out depending on your needs
    }
    private void Process()
    {
        T stuffReturned = method();
        callback(stuffReturned);
    }
}

使用

    void startthework()
    {
        ThreadedExecuter<string> executer = new ThreadedExecuter<string>(someLongFunction, longFunctionComplete);
        executer.Start();
    }
    string someLongFunction()
    {
        while(!workComplete)
            WorkWork();
        return resultOfWork;
    }
    void longFunctionComplete(string s)
    {
        PrintWorkComplete(s);
    }

请注意，longFunctionComplete不会在与starthework相同的线程上执行。

对于采用参数的方法，您始终可以使用闭包，或者扩展类。

答案 6 :(得分：7)

在尝试获取在Thread中执行的方法的返回值时，我遇到了这个线程。我以为我会发布有效的解决方案。

此解决方案使用类来存储要执行的方法（间接）并存储返回值。该类可用于任何函数和任何返回类型。您只需使用返回值类型实例化对象，然后通过lambda（或委托）传递函数进行调用。

C＃3.0实施 

public class ThreadedMethod<T>
{

    private T mResult;
    public T Result 
    {
        get { return mResult; }
        private set { mResult = value; }
    }

    public ThreadedMethod()
    {
    }

    //If supporting .net 3.5
    public void ExecuteMethod(Func<T> func)
    {
        Result = func.Invoke();
    }

    //If supporting only 2.0 use this and 
    //comment out the other overload
    public void ExecuteMethod(Delegate d)
    {
        Result = (T)d.DynamicInvoke();
    }
}

要使用此代码，您可以使用Lambda（或委托）。以下是使用lambdas的示例：

ThreadedMethod<bool> threadedMethod = new ThreadedMethod<bool>();
Thread workerThread = new Thread((unused) => 
                            threadedMethod.ExecuteMethod(() => 
                                SomeMethod()));
workerThread.Start();
workerThread.Join();
if (threadedMethod.Result == false) 
{
    //do something about it...
}

VB.NET 2008实施

使用VB.NET 2008的任何人都不能将lambdas与非值返回方法一起使用。这会影响ThreadedMethod类，因此我们将ExecuteMethod返回函数的值。这不会伤害任何事情。

Public Class ThreadedMethod(Of T)

    Private mResult As T
    Public Property Result() As T
        Get
            Return mResult
        End Get
        Private Set(ByVal value As T)
            mResult = value
        End Set
    End Property

    Sub New()
    End Sub

    'If supporting .net 3.5'
    Function ExecuteMethod(ByVal func As Func(Of T)) As T
        Result = func.Invoke()
        Return Result
    End Function

    'If supporting only 2.0 use this and' 
    'comment out the other overload'
    Function ExecuteMethod(ByVal d As [Delegate]) As T
        Result = DirectCast(d.DynamicInvoke(), T)
        Return Result
    End Function

End Class

答案 7 :(得分：6)

使用最新的.NET Framework，可以使用Task从单独的线程返回值，其中Result属性会阻塞调用线程，直到任务完成：

  Task<MyClass> task = Task<MyClass>.Factory.StartNew(() =>
  {
      string s = "my message";
      double d = 3.14159;
      return new MyClass { Name = s, Number = d };
  });
  MyClass test = task.Result;

有关详细信息，请参阅http://msdn.microsoft.com/en-us/library/dd537613(v=vs.110).aspx

答案 8 :(得分：5)

用于启动线程的C＃中的ThreadStart委托具有返回类型'void'。

如果您希望从线程获得“返回值”，则应该写入共享位置（以适当的线程安全方式），并在线程完成执行时从中读取。

答案 9 :(得分：5)

如果您不想使用BackgroundWorker，只使用常规线程，则可以触发事件以返回如下数据：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Threading;

namespace ThreadWithDataReturnExample
{
    public partial class Form1 : Form
    {
        private Thread thread1 = null;

        public Form1()
        {
            InitializeComponent();

            thread1 = new Thread(new ThreadStart(this.threadEntryPoint));
            Thread1Completed += new AsyncCompletedEventHandler(thread1_Thread1Completed);
        }

        private void startButton_Click(object sender, EventArgs e)
        {
            thread1.Start();
            //Alternatively, you could pass some object
            //in such as Start(someObject);
            //With apprioriate locking, or protocol where
            //no other threads access the object until
            //an event signals when the thread is complete,
            //any other class with a reference to the object 
            //would be able to access that data.
            //But instead, I'm going to use AsyncCompletedEventArgs 
            //in an event that signals completion
        }

        void thread1_Thread1Completed(object sender, AsyncCompletedEventArgs e)
        {
            if (this.InvokeRequired)
            {//marshal the call if we are not on the GUI thread                
                BeginInvoke(new AsyncCompletedEventHandler(thread1_Thread1Completed),
                  new object[] { sender, e });
            }
            else
            {
                //display error if error occurred
                //if no error occurred, process data
                if (e.Error == null)
                {//then success

                    MessageBox.Show("Worker thread completed successfully");
                    DataYouWantToReturn someData = e.UserState as DataYouWantToReturn;
                    MessageBox.Show("Your data my lord: " + someData.someProperty);

                }
                else//error
                {
                    MessageBox.Show("The following error occurred:" + Environment.NewLine + e.Error.ToString());
                }
            }
        }

        #region I would actually move all of this into it's own class
            private void threadEntryPoint()
            {
                //do a bunch of stuff

                //when you are done:
                //initialize object with data that you want to return
                DataYouWantToReturn dataYouWantToReturn = new DataYouWantToReturn();
                dataYouWantToReturn.someProperty = "more data";

                //signal completion by firing an event
                OnThread1Completed(new AsyncCompletedEventArgs(null, false, dataYouWantToReturn));
            }

            /// <summary>
            /// Occurs when processing has finished or an error occurred.
            /// </summary>
            public event AsyncCompletedEventHandler Thread1Completed;
            protected virtual void OnThread1Completed(AsyncCompletedEventArgs e)
            {
                //copy locally
                AsyncCompletedEventHandler handler = Thread1Completed;
                if (handler != null)
                {
                    handler(this, e);
                }
            }
        #endregion

    }
}

答案 10 :(得分：4)

只需使用委托方法。

int val;
Thread thread = new Thread(() => { val = Multiply(1, 2); });
thread.Start();

现在制作可在另一个线程上运行的Multiply函数：

int Multiply(int x, int y)
{
    return x * y;
}

答案 11 :(得分：2)

线程实际上没有返回值。但是，如果创建委托，则可以通过BeginInvoke方法异步调用它。这将在线程池线程上执行该方法。您可以通过EndInvoke拨打任何返回值。

示例：

static int GetAnswer() {
   return 42;
}

...

Func<int> method = GetAnswer;
var res = method.BeginInvoke(null, null); // provide args as needed
var answer = method.EndInvoke(res);

GetAnswer将在线程池线程上执行，完成后您可以通过EndInvoke检索答案，如图所示。

答案 12 :(得分：2)

在为Windows Forms开发时，BackgroundWorker很不错。

假设您想来回传递一个简单的类：

class Anything {
    // Number and Text are for instructional purposes only
    public int Number { get; set; }
    public string Text { get; set; }
    // Data can be any object - even another class
    public object Data { get; set; }
}

我写了一篇简短的课程来完成以下工作：

  • 创建或清除列表
  • 开始循环
  • 在循环中，为列表创建新项目
  • 在循环中，创建一个线程
  • 在循环中，将项目作为参数发送给线程
  • 在循环中，启动线程
  • 在循环中，将线程添加到列表以观看
  • 循环后，加入每个线程
  • 完成所有联接后，显示结果

从线程例程内部开始：

  • 调用锁定，以便一次只能有1个线程进入此例程（其他人必须等待）
  • 发布有关该项目的信息。
  • 修改项目。
  • 线程完成后，数据将显示在控制台上。

添加delegate对于将数据直接发布回主线程非常有用，但如果某些数据项不是线程安全的，则可能需要使用Invoke。

class AnyTask {

    private object m_lock;

    public AnyTask() {
        m_lock = new object();
    }
    // Something to use the delegate
    public event MainDelegate OnUpdate;

    public void Test_Function(int count) {
        var list = new List<Thread>(count);
        for (var i = 0; i < count; i++) {
            var thread = new Thread(new ParameterizedThreadStart(Thread_Task));
            var item = new Anything() {
                Number = i,
                Text = String.Format("Test_Function #{0}", i)
            };
            thread.Start(item);
            list.Add(thread);
        }
        foreach (var thread in list) {
            thread.Join();
        }
    }

    private void MainUpdate(Anything item, bool original) {
        if (OnUpdate != null) {
            OnUpdate(item, original);
        }
    }

    private void Thread_Task(object parameter) {
        lock (m_lock) {
            var item = (Anything)parameter;
            MainUpdate(item, true);
            item.Text = String.Format("{0}; Thread_Task #{1}", item.Text, item.Number);
            item.Number = 0;
            MainUpdate(item, false);
        }
    }

}

要对此进行测试，请创建一个小型控制台应用程序，并将其放在 Program.cs 文件中：

// A delegate makes life simpler
delegate void MainDelegate(Anything sender, bool original);

class Program {

    private const int COUNT = 15;
    private static List<Anything> m_list;

    static void Main(string[] args) {
        m_list = new List<Anything>(COUNT);
        var obj = new AnyTask();
        obj.OnUpdate += new MainDelegate(ThreadMessages);
        obj.Test_Function(COUNT);
        Console.WriteLine();
        foreach (var item in m_list) {
            Console.WriteLine("[Complete]:" + item.Text);
        }
        Console.WriteLine("Press any key to exit.");
        Console.ReadKey();
    }

    private static void ThreadMessages(Anything item, bool original) {
        if (original) {
            Console.WriteLine("[main method]:" + item.Text);
        } else {
            m_list.Add(item);
        }
    }

}

以下是我对此的截图：

Console Output

我希望其他人能够理解我试图解释的内容。

我喜欢在线程上工作并使用代理。他们让C＃变得非常有趣。

附录：适用于VB编码器

我想看看将上面的代码编写为VB控制台应用程序所涉及的内容。转换涉及一些我没想到的事情，所以我会在这里为那些想要知道如何在VB中进行线程化的人更新这个线程。

Imports System.Threading

Delegate Sub MainDelegate(sender As Anything, original As Boolean)

Class Main

    Private Const COUNT As Integer = 15
    Private Shared m_list As List(Of Anything)

    Public Shared Sub Main(args As String())
        m_list = New List(Of Anything)(COUNT)
        Dim obj As New AnyTask()
        AddHandler obj.OnUpdate, New MainDelegate(AddressOf ThreadMessages)
        obj.Test_Function(COUNT)
        Console.WriteLine()
        For Each item As Anything In m_list
            Console.WriteLine("[Complete]:" + item.Text)
        Next
        Console.WriteLine("Press any key to exit.")
        Console.ReadKey()
    End Sub

    Private Shared Sub ThreadMessages(item As Anything, original As Boolean)
        If original Then
            Console.WriteLine("[main method]:" + item.Text)
        Else
            m_list.Add(item)
        End If
    End Sub

End Class

Class AnyTask

    Private m_lock As Object

    Public Sub New()
        m_lock = New Object()
    End Sub
    ' Something to use the delegate
    Public Event OnUpdate As MainDelegate

    Public Sub Test_Function(count As Integer)
        Dim list As New List(Of Thread)(count)
        For i As Int32 = 0 To count - 1
            Dim thread As New Thread(New ParameterizedThreadStart(AddressOf Thread_Task))
            Dim item As New Anything()
            item.Number = i
            item.Text = String.Format("Test_Function #{0}", i)
            thread.Start(item)
            list.Add(thread)
        Next
        For Each thread As Thread In list
            thread.Join()
        Next
    End Sub

    Private Sub MainUpdate(item As Anything, original As Boolean)
        RaiseEvent OnUpdate(item, original)
    End Sub

    Private Sub Thread_Task(parameter As Object)
        SyncLock m_lock
            Dim item As Anything = DirectCast(parameter, Anything)
            MainUpdate(item, True)
            item.Text = [String].Format("{0}; Thread_Task #{1}", item.Text, item.Number)
            item.Number = 0
            MainUpdate(item, False)
        End SyncLock
    End Sub

End Class


Class Anything
    ' Number and Text are for instructional purposes only
    Public Property Number() As Integer
        Get
            Return m_Number
        End Get
        Set(value As Integer)
            m_Number = value
        End Set
    End Property
    Private m_Number As Integer
    Public Property Text() As String
        Get
            Return m_Text
        End Get
        Set(value As String)
            m_Text = value
        End Set
    End Property
    Private m_Text As String
    ' Data can be anything or another class
    Public Property Data() As Object
        Get
            Return m_Data
        End Get
        Set(value As Object)
            m_Data = value
        End Set
    End Property
    Private m_Data As Object
End Class

答案 13 :(得分：1)

class Program
{
    static void Main(string[] args)
    {
        string returnValue = null;
       new Thread(
          () =>
          {
              returnValue =test() ; 
          }).Start();
        Console.WriteLine(returnValue);
        Console.ReadKey();
    }

    public static string test()
    {
        return "Returning From Thread called method";
    }
}

答案 14 :(得分：1)

一个简单的解决方案是通过ref将参数传递给线程中运行的函数，并在线程中更改其值。

       // create a list of threads
        List<Thread> threads = new List<Thread>();


        //declare the ref params
        bool is1 = false;
        bool is2 = false;

        threads.Add(new Thread(() => myFunction(someVar, ref is1)));
        threads.Add(new Thread(() => myFunction(someVar, ref is2)));

        threads.ForEach(x => x.Start());

        // wait for threads to finish
        threads.ForEach(x => x.Join());

        //check the ref params
        if (!is1)
        {
          //do something
        }

        if (!is2)
        {
           //do somethign else
        }

如果您无法更改踏板中正在运行的功能，则可以将其换行另一个功能：

 bool theirFunction(var someVar){
   return false;
}


 void myFunction(var someVar ref bool result){
  result = theirFunction(myVar);
 }

答案 15 :(得分：0)

可以使用此代码：

 private Object MyThread(Object Data)
      {
        Object response = null;
        Thread newThread = new Thread(() =>
        {
            response = MyFunction(Data);
            //MyFunction Is Function that you Define
        });
        newThread.Start();
        newThread.Join();
        return response;
      }

答案 16 :(得分：0)

class Program
{
    public static void ActionResultPrint(string i)
    {
        Console.WriteLine(i);
    }

    static void Main(string[] args)
    {
        var tl = new List<Thread>();

        tl.Add(new Thread(() => Run(10, ActionResultPrint)));
        tl.Add(new Thread(() => Run(20, ActionResultPrint)));
        tl.ForEach(x => x.Start());
        tl.ForEach(x => x.Join());
    }

    public static void Run(int j, Action<string> action)
    {
        string rvalue = string.Empty;

        for (int i = 0; i <= j; i++)
        {
            Thread.Sleep(100);
            rvalue = i.ToString();
            Console.WriteLine(rvalue);
        }
        action($@"output {j}");
    }
}

答案 17 :(得分：0)

使用线程时，可以通过以下方式传递和返回值：

int value = -1;
  Thread t1 = new Thread(() => { value = compute(a); });
   t1.Start();
 if(value!=-1)
 {...}

   public int compute(int[] a1)
    {
    //...code logic
        return -1;
    }

答案 18 :(得分：-1)

我不是线程方面的专家，这就是为什么我这样做的原因：

我创建了一个设置文件和

新线程内：

Setting.Default.ValueToBeSaved;
Setting.Default.Save();

然后我会在需要的时候拿起那个值。

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