【发布时间】：2009-06-12 12:31:19
【问题描述】：
我对带有后台进程的响应式 GUI 的处理方法是否正确？如果没有，请批评并提供改进。尤其要指出哪些代码可能会遇到死锁或竞争条件。
工作线程需要能够被取消并报告它的进度。我没有使用 BackgroundWorker，因为我看到的所有示例在 Form 本身上都有 Process 代码，而不是单独的对象。我曾考虑为 BackgroundWorker 继承 LongRunningProcess，但我认为这会在对象上引入不必要的方法。理想情况下，我不希望表单引用进程（“_lrp”），但我不知道如何取消进程，除非我在 LRP 上有一个检查标志的事件在调用者身上，但这似乎不必要地复杂，甚至可能是错误的。
Windows 窗体（编辑：将 *.EndInvoke 调用移至回调）
public partial class MainForm : Form
{
MethodInvoker _startInvoker = null;
MethodInvoker _stopInvoker = null;
bool _started = false;
LongRunningProcess _lrp = null;
private void btnAction_Click(object sender, EventArgs e)
{
// This button acts as a Start/Stop switch.
// GUI handling (changing button text etc) omitted
if (!_started)
{
_started = true;
var lrp = new LongRunningProcess();
_startInvoker = new MethodInvoker((Action)(() => Start(lrp)));
_startInvoker.BeginInvoke(new AsyncCallback(TransferEnded), null);
}
else
{
_started = false;
_stopInvoker = new MethodInvoker(Stop);
_stopInvoker.BeginInvoke(Stopped, null);
}
}
private void Start(LongRunningProcess lrp)
{
// Store a reference to the process
_lrp = lrp;
// This is the same technique used by BackgroundWorker
// The long running process calls this event when it
// reports its progress
_lrp.ProgressChanged += new ProgressChangedEventHandler(_lrp_ProgressChanged);
_lrp.RunProcess();
}
private void Stop()
{
// When this flag is set, the LRP will stop processing
_lrp.CancellationPending = true;
}
// This method is called when the process completes
private void TransferEnded(IAsyncResult asyncResult)
{
if (this.InvokeRequired)
{
this.BeginInvoke(new Action<IAsyncResult>(TransferEnded), asyncResult);
}
else
{
_startInvoker.EndInvoke(asyncResult);
_started = false;
_lrp = null;
}
}
private void Stopped(IAsyncResult asyncResult)
{
if (this.InvokeRequired)
{
this.BeginInvoke(new Action<IAsyncResult>(Stopped), asyncResult);
}
else
{
_stopInvoker.EndInvoke(asyncResult);
_lrp = null;
}
}
private void _lrp_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
// Update the progress
// if (progressBar.InvokeRequired) etc...
}
}
后台进程：
public class LongRunningProcess
{
SendOrPostCallback _progressReporter;
private readonly object _syncObject = new object();
private bool _cancellationPending = false;
public event ProgressChangedEventHandler ProgressChanged;
public bool CancellationPending
{
get { lock (_syncObject) { return _cancellationPending; } }
set { lock (_syncObject) { _cancellationPending = value; } }
}
private void ReportProgress(int percentProgress)
{
this._progressReporter(new ProgressChangedEventArgs(percentProgress, null));
}
private void ProgressReporter(object arg)
{
this.OnProgressChanged((ProgressChangedEventArgs)arg);
}
protected virtual void OnProgressChanged(ProgressChangedEventArgs e)
{
if (ProgressChanged != null)
ProgressChanged(this, e);
}
public bool RunProcess(string data)
{
// This code should be in the constructor
_progressReporter = new SendOrPostCallback(this.ProgressReporter);
for (int i = 0; i < LARGE_NUMBER; ++i)
{
if (this.CancellationPending)
break;
// Do work....
// ...
// ...
// Update progress
this.ReportProgress(percentageComplete);
// Allow other threads to run
Thread.Sleep(0)
}
return true;
}
}
【问题讨论】：
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投票结束，因为“请批评”听起来不像一个问题。
标签： c# multithreading concurrency