Question

怎样保证回调函数在主线程中执行

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Answer 1

可以通过线程池ThreadPool来解决，使用ThreadPool.QueueUserWorkItem(回调函数，object)，将参数封装在一个类的对象中，传给回调函数去执行。
TheadPool的用法：
1、创建一个ManualResetEvent的对象，就像一个信号灯，指示线程的挂起和执行；
2、ManualResetEvent对象创建时，可以指定默认状态：true为有信号，false为无信号；
3、调用Reset()方法重置状态；
4、调用WaitOne()方法，使线程处于等待状态；
5、调用Set()方法设置状态。
using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using System.Collections;

namespace Demo
{
public class ParamObject
{
public int number;
public ParamObject (int number)
{
this.number = number;
}
}

public class ThreadClass
{
public Hashtable aHashTable;
public ManualResetEvent aManualResetEvent;
public static int iCount = 0;
public static int iMaxCount = 0;

public ThreadClass(int maxCount)
{
aHashTable = new Hashtable(maxCount);
iMaxCount = maxCount;
}

public void ThreadRun(object aParamObject)
{
Console.WriteLine("HashCode: {0}, Number in Object: {1}", Thread.CurrentThread.GetHashCode(), ((ParamObject)aParamObject).number);
lock (aHashTable)
{
if (!aHashTable.ContainsKey(Thread.CurrentThread.GetHashCode()))
{
aHashTable.Add(Thread.CurrentThread.GetHashCode(), 0);
}
aHashTable[Thread.CurrentThread.GetHashCode()] = (int)aHashTable[Thread.CurrentThread.GetHashCode()] + 1;
}
Thread.Sleep(3000);

Interlocked.Increment(ref iCount);
if (iCount == iMaxCount)
{
Console.WriteLine("Setting aManualResetEvent...");
aManualResetEvent.Set();
}
}
}

class Program
{
public static void Main(string[] args)
{
bool enableThreadPool = false;
int iMaxCount = 20;
ManualResetEvent aManualResetEvent = new ManualResetEvent(false);

Console.WriteLine("Insert {0} items to Thread Pool.", iMaxCount);
ThreadClass aThreadClass = new ThreadClass(iMaxCount);
aThreadClass.aManualResetEvent = aManualResetEvent;

// First, add an item to check if your system supports ThreadPool API function or not.
try
{
ThreadPool.QueueUserWorkItem(new WaitCallback(aThreadClass.ThreadRun), new ParamObject(0));
enableThreadPool = true;
}
catch (NotSupportedException ex)
{
Console.WriteLine("Thread Pool API is not supported in this system.");
enableThreadPool = false;
}

if (enableThreadPool)
{
for (int i = 1; i < iMaxCount; i++)
{
ThreadPool.QueueUserWorkItem(new WaitCallback(aThreadClass.ThreadRun), new ParamObject(i));
}
Console.WriteLine("Waiting for thread pool to drain");
aManualResetEvent.WaitOne(Timeout.Infinite, true);

Console.WriteLine("Thread Pool has been drained.");
Console.WriteLine("Load threads info:");
foreach (object key in aThreadClass.aHashTable.Keys)
{
Console.WriteLine("Key: {0}, Value: {1}", key, aThreadClass.aHashTable[key]);
}
}
Console.ReadLine();
}
}
}