我在编写的代码中遇到了一个奇怪的死锁。
这个想法是实现一个异步操作， Stop 是同步的 - 调用者必须等到它完成。我已经将实际工作的部分简化为简单的属性增量（++Value，见下文）;但实际上，调用了一个对线程非常敏感的繁重的COM组件。
我遇到的死锁是在Stop()方法中，我明确等待识别已完成操作的手动重置事件。
任何想法我可能做错了什么？代码应该是独立的，并且可以单独编译。
using System;
using System.ComponentModel;
using System.Threading;
using System.Windows.Forms;
using ThreadingTimer = System.Threading.Timer;
namespace CS_ManualResetEvent
{
class AsyncOperation
{
ThreadingTimer myTimer; //!< Receives periodic ticks on a ThreadPool thread and dispatches background worker.
ManualResetEvent myBgWorkerShouldIterate; //!< Fired when background worker must run a subsequent iteration of its processing loop.
ManualResetEvent myBgWorkerCompleted; //!< Fired before the background worker routine exits.
BackgroundWorker myBg; //!< Executes a background tasks
int myIsRunning; //!< Nonzero if operation is active; otherwise, zero.
public AsyncOperation()
{
var aTimerCallbac = new TimerCallback(Handler_Timer_Tick);
myTimer = new ThreadingTimer(aTimerCallbac, null, Timeout.Infinite, 100);
myBg = new BackgroundWorker();
myBg.DoWork += new DoWorkEventHandler(Handler_BgWorker_DoWork);
myBgWorkerShouldIterate = new ManualResetEvent(false);
myBgWorkerCompleted = new ManualResetEvent(false);
}
public int Value { get; set; }
/// <summary>Begins an asynchronous operation.</summary>
public void Start()
{
Interlocked.Exchange(ref myIsRunning, 1);
myTimer.Change(0, 100);
myBg.RunWorkerAsync(null);
}
/// <summary>Stops the worker thread and waits until it finishes.</summary>
public void Stop()
{
Interlocked.Exchange(ref myIsRunning, 0);
myTimer.Change(-1, Timeout.Infinite);
// fire the event once more so that the background worker can finish
myBgWorkerShouldIterate.Set();
// Wait until the operation completes; DEADLOCK occurs HERE!!!
myBgWorkerCompleted.WaitOne();
// Restore the state of events so that we could possibly re-run an existing component.
myBgWorkerCompleted.Reset();
myBgWorkerShouldIterate.Reset();
}
void Handler_BgWorker_DoWork(object sender, EventArgs theArgs)
{
while (true)
{
myBgWorkerShouldIterate.WaitOne();
if (myIsRunning == 0)
{
//Thread.Sleep(5000); //What if it takes some noticeable time to finish?
myBgWorkerCompleted.Set();
break;
}
// pretend we're doing some valuable work
++Value;
// The event will be set back in Handler_Timer_Tick or when the background worker should finish
myBgWorkerShouldIterate.Reset();
}
// exit
}
/// <summary>Processes tick events from a timer on a dedicated (thread pool) thread.</summary>
void Handler_Timer_Tick(object state)
{
// Let the asynchronous operation run its course.
myBgWorkerShouldIterate.Set();
}
}
public partial class Form1 : Form
{
private AsyncOperation myRec;
private Button btnStart;
private Button btnStop;
public Form1()
{
InitializeComponent();
}
private void Handler_StartButton_Click(object sender, EventArgs e)
{
myRec = new AsyncOperation();
myRec.Start();
btnStart.Enabled = false;
btnStop.Enabled = true;
}
private void Handler_StopButton_Click(object sender, EventArgs e)
{
myRec.Stop();
// Display the result of the asynchronous operation.
MessageBox.Show (myRec.Value.ToString() );
btnStart.Enabled = true;
btnStop.Enabled = false;
}
private void InitializeComponent()
{
btnStart = new Button();
btnStop = new Button();
SuspendLayout();
// btnStart
btnStart.Location = new System.Drawing.Point(35, 16);
btnStart.Size = new System.Drawing.Size(97, 63);
btnStart.Text = "Start";
btnStart.Click += new System.EventHandler(Handler_StartButton_Click);
// btnStop
btnStop.Enabled = false;
btnStop.Location = new System.Drawing.Point(138, 16);
btnStop.Size = new System.Drawing.Size(103, 63);
btnStop.Text = "Stop";
btnStop.Click += new System.EventHandler(Handler_StopButton_Click);
// Form1
ClientSize = new System.Drawing.Size(284, 94);
Controls.Add(this.btnStop);
Controls.Add(this.btnStart);
Text = "Form1";
ResumeLayout(false);
}
}
static class Program
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}
}
}
答案 0 :(得分：1)
似乎所有你要做的就是有一个异步任务，从按下按钮开始，当按下另一个按钮时停止。鉴于此，您似乎过度复杂化了任务。考虑使用专门用于取消异步操作的东西，例如CancellationToken。异步任务只需要在while循环中检查取消令牌的状态（而不是while(true)），stop方法就像在CancellationTokenSource上调用取消一样简单
private CancellationTokenSource cancellationSource;
private Task asyncOperationCompleted;
private void button1_Click(object sender, EventArgs e)
{
//cancel previously running operation before starting a new one
if (cancellationSource != null)
{
cancellationSource.Cancel();
}
else //take out else if you want to restart here when `start` is pressed twice.
{
cancellationSource = new CancellationTokenSource();
TaskCompletionSource<object> tcs = new TaskCompletionSource<object>();
asyncOperationCompleted = tcs.Task;
BackgroundWorker bgw = new BackgroundWorker();
bgw.DoWork += (_, args) => DoWork(bgw, cancellationSource);
bgw.ProgressChanged += (_, args) => label1.Text = args.ProgressPercentage.ToString();
bgw.WorkerReportsProgress = true;
bgw.RunWorkerCompleted += (_, args) => tcs.SetResult(true);
bgw.RunWorkerAsync();
}
}
private void DoWork(BackgroundWorker bgw, CancellationTokenSource cancellationSource)
{
int i = 0;
while (!cancellationSource.IsCancellationRequested)
{
Thread.Sleep(1000);//placeholder for real work
bgw.ReportProgress(i++);
}
}
private void StopAndWaitOnBackgroundTask()
{
if (cancellationSource != null)
{
cancellationSource.Cancel();
cancellationSource = null;
asyncOperationCompleted.Wait();
}
}
答案 1 :(得分：-3)
将此代码放在++ Value下;在Handler_BgWorker_DoWork中。然后在调试窗口中看到输出时按下按钮。然后发生死锁。
int i = 0;
while (i++ < 100) {
System.Diagnostics.Debug.Print("Press the button now");
Thread.Sleep(300);
Application.DoEvents();
}