HttpWebRequests阻止来自另一个线程的UI线程

Question

我在Seaprate线程上执行多个HttpWebRequests，但是在调用Start()之后几乎所有时间我的UI线程都被阻塞，我不知道为什么，这是最重要的代码：

private void Start()
{
    for (int i = 0; i < 10; i++)
    {
        var todo = UrlStack.UrlPartitions.First();
        UrlStack.UrlPartitions.Remove(todo);
        ThreadPool.QueueUserWorkItem(new WaitCallback(ScanSites), todo);
    }
}
private void ScanSites(object o)
{
    var ToDo = (List<string>)o;
    foreach (string Url in ToDo)
    {
        var state = MakeRequest(Url);
        var website = WebsiteProcessing.ProcessResponse(state);
        if (website != null)
        {
            Websites.Add(website);
            WebsitesCount++;
            this.UIThread(() => lblCrawledWebsites.Text = WebsitesCount.ToString());
        }
    }
}
private static RequestState MakeRequest(string url)
{
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
    ...
    RequestState state = new RequestState();
    HttpWebResponse response = null;
    Stream responseStream = null;
    StreamReader sr = null;

    try
    {
        response = (HttpWebResponse)request.GetResponse();
        responseStream = response.GetResponseStream();
        sr = new StreamReader(responseStream);
        state.Request = (HttpWebRequest)request;
        state.Response = (HttpWebResponse)response;
        string strContent = sr.ReadToEnd();
        state.ResponseContent = new StringBuilder(strContent);
    }
    catch
    {
        return null;
    }

    finally
    {
        if (responseStream != null)
            responseStream.Close();
        if (sr != null)
            sr.Close();
        if (response != null)
            response.Close();
    }

    return state;
}

Answer 1

我发现了令我非常惊讶的错。 这是一个具有20-30个正则表达式的自定义类，用于使用HtmlAgilityPack提取文本后剥离剩余的HTML，我仍然不明白的是后台线程如何阻止UI，CPU峰值从未超过50％。

Answer 2

可能是因为这个电话吗？

this.UIThread(() => lblCrawledWebsites.Text = WebsitesCount.ToString()); 

您没有提供UIThread的定义，但看起来像是在编组对UI线程的调用。 在这种情况下，如果“待办事项”列表中有许多URL，则可能会阻塞UI线程。