FtpWebRequest 异步调用问题

[yangjiaqm]

直接上代码了，以下代码，
private void Window_Loaded(object sender, RoutedEventArgs e)
{

Abc();
Abc();
Abc();
}

private void Abc()
{
FtpWebRequest ftpRequest = null;

try
{
ftpRequest = (FtpWebRequest)FtpWebRequest.Create(new Uri("ftp://xxx.xxx.xxx.xxx/storage/7788"));
ftpRequest.UseBinary = true;
ftpRequest.Credentials = new NetworkCredential("xxx", "xxx");
ftpRequest.Method = "LIST";// WebRequestMethods.Ftp.GetFileSize;
ftpRequest.Timeout = 5000;
ftpRequest.ReadWriteTimeout = 5000;

ftpRequest.BeginGetResponse(new AsyncCallback(EndGetResponseLengthCallback), null);
MessageBox.Show("Q");
}
catch (Exception ex)
{
if (ftpRequest != null)
{
ftpRequest.Abort();
}
}
finally
{
Console.WriteLine("Step1 Completed");
}
}

private void EndGetResponseLengthCallback(IAsyncResult ar)
{
System.Windows.Application.Current.Dispatcher.Invoke(new Action(() => {
MessageBox.Show("A");
}));
FtpWebResponse ftpResponse = null;
try
{
ftpResponse = (FtpWebResponse)ftpRequest.EndGetResponse(ar);
string fileUploadLog = " 服务返回状态码: " + ftpResponse.StatusCode + " 状态描述信息: " + ftpResponse.StatusDescription;
Console.WriteLine(fileUploadLog);
}
catch (Exception ex)
{
if (ftpRequest != null)
{
ftpRequest.Abort();
}
}
finally
{
if (ftpRequest != null)
{
ftpRequest.Abort();
}
}
}
}

上述代码相信是一个比较简单的获取ftp目录列表的代码，网上很多例子都是这么写的，但是，我实际测试过程中发现，在我断开网络连接的时候，启动程序，在主线程中连续三次调用Abc（）方法，只有2次会运行到异步回调函数（EndGetResponseLengthCallback），第三次异步调用后一直没有进回调函数，请大神忙帮助一下，看看这代码如何才能让第三次及以后的异步调用都进回调函数。

[qbilbo]

ftpRequest.BeginGetResponse(new AsyncCallback(EndGetResponseLengthCallback), ftpRequest); private void EndGetResponseLengthCallback(IAsyncResult ar) { FtpWebRequest ftpRequest = (FtpWebRequest )ar.AsyncState; ...... }

[yangjiaqm]

private void Abc() { FtpWebRequest ftpRequest = null; try { ftpRequest = (FtpWebRequest)FtpWebRequest.Create(new Uri("ftp://xxx.xxx.xxx.xxx/storage")); ftpRequest.UseBinary = true; ftpRequest.Credentials = new NetworkCredential("xxxx", "xxxx"); ftpRequest.Method = "LIST";// WebRequestMethods.Ftp.GetFileSize; ftpRequest.Timeout = 5000; ftpRequest.ReadWriteTimeout = 5000; FtpRespondLengthAsyncState asyncState = new FtpRespondLengthAsyncState(); asyncState.webRequest = ftpRequest; asyncState.callBack = null; ftpRequest.BeginGetResponse(new AsyncCallback(EndGetResponseLengthCallback), asyncState); } catch (Exception ex) { if (ftpRequest != null) { ftpRequest.Abort(); } } finally { Console.WriteLine("Step1 Completed"); } } private void EndGetResponseLengthCallback(IAsyncResult ar) { if (ar == null || ar.AsyncState == null || !(ar.AsyncState is FtpRespondLengthAsyncState)) { return; } FtpRespondLengthAsyncState asyncState = (FtpRespondLengthAsyncState)ar.AsyncState; if (asyncState == null || asyncState.webRequest == null) { return; } FtpWebRequest ftpRequest = asyncState.webRequest; Action<bool, long> callback = asyncState.callBack; FtpWebResponse ftpResponse = null; try { ftpResponse = (FtpWebResponse)ftpRequest.EndGetResponse(ar); string fileUploadLog = asyncState.Arg1.ToString() + " 服务返回状态码: " + ftpResponse.StatusCode + " 状态描述信息: " + ftpResponse.StatusDescription; Console.WriteLine(fileUploadLog); } catch (Exception ex) { if (ftpRequest != null) { ftpRequest.Abort(); } } finally { if (ftpRequest != null) { ftpRequest.Abort(); } } } 虽然代码已经修改了，但是还是不行。

[qbilbo]

改错了，看我的第一句。

[yangjiaqm]

qbilbo： 没有用的。第一句是BeginGetResponse，你我写的都是一样的，只不过第二个参数不一样罢了。我传递的参数包含了ftpRequest。用你的方式调用我也试了，一样的，连续调用三次，2次有进回调函数，最后1次不进回调。根本不是现在写的代码的问题，如果是在有网络的情况下，会3次都进回调的。

[yangjiaqm]

我自己解决了。
System.Net.ServicePointManager.DefaultConnectionLimit = 10;

默认值是2，设置大一点就可以了。