我正在使用WebRequest.BeginGetResponse进行异步请求以从服务器下载文件。一切都很好,但我想同时下载5个文件。在Java中我会使用固定的线程池,但我不知道如何在C#中做同样的事情。有什么想法吗?
class HttpFetcher
{
public void MakeRequest(Uri uri)
{
WebRequest request = WebRequest.Create(uri);
request.Proxy = null;
RequestState requestState = new RequestState();
requestState.Request = request;
IAsyncResult result = (IAsyncResult) request.BeginGetResponse(new AsyncCallback(ResponseCallback), requestState);
ThreadPool.RegisterWaitForSingleObject(result.AsyncWaitHandle, new WaitOrTimerCallback(TimeOutCallback), request, 1000, true);
}
private void ResponseCallback(IAsyncResult result)
{
try
{
RequestState requestState = (RequestState)result.AsyncState;
WebRequest request = requestState.Request;
requestState.Response = request.EndGetResponse(result);
Stream responseStream = requestState.Response.GetResponseStream();
requestState.ResponseStream = responseStream;
IAsyncResult asynchronousResultRead = responseStream.BeginRead(requestState.BufferRead, 0, 1024, new AsyncCallback(ReadCallback), requestState);
}
catch (Exception ex)
{
Console.WriteLine("Exception raised!");
Console.WriteLine("Message : {0}", ex.Message);
RequestState state = (RequestState)result.AsyncState;
if (state.Response != null)
state.Response.Close();
}
}
private void ReadCallback(IAsyncResult result)
{
try
{
RequestState requestState = (RequestState)result.AsyncState;
Stream responseStream = requestState.ResponseStream;
int bytesRead = responseStream.EndRead(result);
if (bytesRead > 0)
{
requestState.RequestData.Append(Encoding.ASCII.GetString(requestState.BufferRead, 0, bytesRead));
IAsyncResult asynchronousResult = responseStream.BeginRead(requestState.BufferRead, 0, 1024, new AsyncCallback(ReadCallback), requestState);
}
else
{
Console.WriteLine("\nThe HTML page Contents are: ");
if (requestState.RequestData.Length > 1)
{
string sringContent;
sringContent = requestState.RequestData.ToString();
//Console.WriteLine(sringContent);
}
Console.WriteLine("\nPress 'Enter' key to continue........");
responseStream.Close();
}
}
catch (WebException e)
{
Console.WriteLine("WebException raised!");
Console.WriteLine("\n{0}", e.Message);
Console.WriteLine("\n{0}", e.Status);
}
catch (Exception e)
{
Console.WriteLine("Exception raised!");
Console.WriteLine("Source : {0}", e.Source);
Console.WriteLine("Message : {0}", e.Message);
}
}
private void TimeOutCallback(object state, bool timedOut)
{
if (timedOut)
{
WebRequest request = (WebRequest)state;
if (state != null)
{
request.Abort();
}
}
}
}
答案 0 :(得分:1)
您可以使用Task.Factory.FromAsync()
并使用Task Scheduler that limits the Degree of Concurrency
这里没有深入FromAsync()
这是一个非常简单的例子,它显示最多有5个任务并行运行,无论有多少个队列排队:
public static void Main()
{
var scheduler = new LimitedConcurrencyLevelTaskScheduler(5);
TaskFactory factory = new TaskFactory(scheduler);
for (int i = 0; i < 50; i++)
{
int idx = i;
var newTask = factory.StartNew(() =>
{
Console.WriteLine("Starting " + idx);
Thread.Sleep(5000);
});
}
Console.ReadLine();
}