我有一个 Stream 对象，我正在使用 BeginRead 开始（显然）读入缓冲区；读取完成后调用 AsyncCallback 函数。在这个函数中，我可以检查用户是否想要获得下一个“块”并再次启动 BeginRead 过程。
我遇到的问题是用户可能会在流仍在读取时选择取消（所以在调用 AsyncCallback 函数之前），那么如何取消流的读取？
只是为了进一步解释这个问题 - 如果我将 BackgroundWorker 与 Streams Read 方法或异步 BeginRead 方法一起使用，我似乎会得到相同的结果。在我可以检查流是否应该停止读取之前，用户可能会等待任何时间长度的 Read/BeginRead 方法完成。
编辑：下面的代码应该可以完成这项工作，我距离 C# 中任何体面的东西还有一百万英里，所以它很可能有几个错误，因为我怀疑它是否完美，尽管它确实展示了解决方案。
简而言之，CWorkManager 管理一定数量的线程（保存在 CWorkerDetail 类中）。每个 CWorkerDetail 都有一个状态，可以是 EWaiting 表示可以启动工作程序，EReading 表示工作程序正在从源读取，在此期间可以立即停止工作程序，EWriting 将读取的数据保存到磁盘 -这不能立即停止，并且必须在线程停止之前完成此过程。最后是 EAborting，如果工人应该尽快被中止，则由经理设置；现在，只有当工作人员处于无法中断的事情（例如写入磁盘）中间时才设置。
现在，实际上并没有进行任何读取或写入，因为这只会使主要解决方案复杂化（这基本上只是 StopWorker 函数检查 CWorker 的标志以查看它是否可以立即中止）；因此，我们只是让线程休眠。
GUI 端相当简单，只有一个列表框（显示每个工作人员的状态）和一个停止和启动按钮。所有代码都在下面，希望这对某人有所帮助，但正如我所说，我对 C# 并不精通，所以请注意错误等...
CWorkManager.cs：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
namespace ThreadApplication {
//A worker that spawns a number of threads (managed internally) that does nothing useful at all.
public class CWorkManager {
//The status of the worker.
public enum EWorkerStatus {
EWaiting,
EReading,
EWriting,
EAborting,
}
//Holds all data relevant to the worker.
private class CWorkerDetails {
//Simple variables.
private readonly Object _Lock=new Object();
private Thread gThread;
private EWorkerStatus gStatus;
private CWorkManager gParentInstance;
private int gIndex;
//Simple constructor.
public CWorkerDetails(int aIndex, CWorkManager aParentInstance, Thread aThread, EWorkerStatus aStatus) {
gIndex=aIndex;
gParentInstance=aParentInstance;
gThread=aThread;
gStatus=aStatus;
}
//Simple get set methods.
public Thread GetThread() { lock(_Lock) { return gThread; } }
public EWorkerStatus GetStatus() { lock(_Lock) { return gStatus; } }
//Sets the status and automatically updates the GUI.
public void SetStatus(EWorkerStatus aStatus) {
lock(_Lock) {
gStatus=aStatus;
Form1.gInstance.Invoke(new UpdateGUIDelegate(gParentInstance.UpdateGUI), new object[] { gIndex, GetStatus() });
}
}
}
//Worker variable.
private List<CWorkerDetails> gWorkers;
//Simple constructor.
public CWorkManager(int aWorkerCount){
gWorkers=new List<CWorkerDetails>();
for(int tIndex=0; tIndex<aWorkerCount; tIndex++)
gWorkers.Add(null);
}
//Creates and starts the worker.
public void StartWorker(int aWorkerIndex) {
//Create a new worker if there is none or if it is waiting to start.
if(gWorkers.ElementAt(aWorkerIndex)==null||gWorkers.ElementAt(aWorkerIndex).GetStatus()==EWorkerStatus.EWaiting)
gWorkers[aWorkerIndex]=new CWorkerDetails(aWorkerIndex, this, new Thread(new ParameterizedThreadStart(WorkerMethod)), EWorkerStatus.EWaiting);
//If the worker is waiting to start, then start.
if(gWorkers.ElementAt(aWorkerIndex).GetStatus()==EWorkerStatus.EWaiting)
gWorkers.ElementAt(aWorkerIndex).GetThread().Start(gWorkers.ElementAt(aWorkerIndex));
}
//Stops the worker.
public void StopWorker(int aWorkerIndex) {
//Do nothing if the worker is null.
if(gWorkers.ElementAt(aWorkerIndex)==null)
return;
//Do nothing if the worker is waiting.
if(gWorkers.ElementAt(aWorkerIndex).GetStatus()==EWorkerStatus.EWaiting)
return;
//If the worker is reading we can abort instantly.
if(gWorkers[aWorkerIndex].GetStatus()==EWorkerStatus.EReading) {
gWorkers[aWorkerIndex].GetThread().Abort();
gWorkers[aWorkerIndex].SetStatus(EWorkerStatus.EWaiting);
return;
}
//Since the worker is not reading or waiting, we have to request the
//worker to abort by itself.
gWorkers[aWorkerIndex].SetStatus(EWorkerStatus.EAborting);
}
//Updates the GUI.
private delegate void UpdateGUIDelegate(int aIndex, EWorkerStatus aStatus);
private void UpdateGUI(int aIndex, EWorkerStatus aStatus) {
Form1.gInstance.SetThreadStatus(aIndex, aStatus);
}
//This method is where all the real work happens.
private void WorkerMethod(Object aWorker) {
//Fetch worker.
CWorkerDetails mWorker=(CWorkerDetails)aWorker;
//Loop forever, the thread will exit itself when required.
while(true) {
//Is the worker status aborting - if so we stop here.
if(mWorker.GetStatus()==EWorkerStatus.EAborting) {
mWorker.SetStatus(EWorkerStatus.EWaiting);
return;
}
//This would normally be reading from a stream which would cause the thread
//to block, simulate this by just sleeping the thread.
mWorker.SetStatus(EWorkerStatus.EReading);
Thread.Sleep(3000);
//Is the worker status aborting - if so we stop here.
if(mWorker.GetStatus()==EWorkerStatus.EAborting) {
mWorker.SetStatus(EWorkerStatus.EWaiting);
return;
}
//All data has been read, set status to writing and again simulate by
//sleeping the thread.
mWorker.SetStatus(EWorkerStatus.EWriting);
Thread.Sleep(3000);
}
}
}
}
Form1.cs：
包含：
- 一个列表框 (ListBox_WorkerStatus)
- 一个按钮（Button_Start）
- 一个按钮 (Button_Stop)
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace ThreadApplication {
public partial class Form1:Form {
public static Form1 gInstance;
private CWorkManager gManager;
public Form1() {
InitializeComponent();
Button_Start.Click+=new EventHandler(Button_Start_Click);
Button_Stop.Click+=new EventHandler(Button_Stop_Click);
gInstance=this;
for(int tIndex=0; tIndex<5; tIndex++)
ListBox_WorkerStatus.Items.Add("Created");
gManager=new CWorkManager(ListBox_WorkerStatus.Items.Count);
}
public void SetThreadStatus(int aIndex, CWorkManager.EWorkerStatus aStatus) {
ListBox_WorkerStatus.Items[aIndex]=aStatus.ToString();
}
private void Button_Start_Click(object sender, EventArgs e) {
if(ListBox_WorkerStatus.SelectedIndex>=0) {
gManager.StartWorker(ListBox_WorkerStatus.SelectedIndex);
}
}
private void Button_Stop_Click(object sender, EventArgs e) {
if(ListBox_WorkerStatus.SelectedIndex>=0) {
gManager.StopWorker(ListBox_WorkerStatus.SelectedIndex);
}
}
private void Form1_FormClosed(object sender, FormClosedEventArgs e) {
for(int tIndex=0; tIndex<ListBox_WorkerStatus.Items.Count; tIndex++) {
gManager.StopWorker(tIndex);
}
}
}
}