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I requested 100 pages that all 404. I wrote

    {
    var s = DateTime.Now;
    for(int i=0; i < 100;i++)
        DL.CheckExist("http://google.com/lol" + i.ToString() + ".jpg");
    var e = DateTime.Now;
    var d = e-s;
        d=d;
        Console.WriteLine(d);
    }

static public bool CheckExist(string url)
{
    HttpWebRequest wreq = null;
    HttpWebResponse wresp = null;
    bool ret = false;

    try
    {
        wreq = (HttpWebRequest)WebRequest.Create(url);
        wreq.KeepAlive = true;
        wreq.Method = "HEAD";
        wresp = (HttpWebResponse)wreq.GetResponse();
        ret = true;
    }
    catch (System.Net.WebException)
    {
    }
    finally
    {
        if (wresp != null)
            wresp.Close();
    }
    return ret;
}

Two runs show it takes 00:00:30.7968750 and 00:00:26.8750000. Then i tried firefox and use the following code

<html>
<body>
<script type="text/javascript">
for(var i=0; i<100; i++)
    document.write("<img src=http://google.com/lol" + i + ".jpg><br>");
</script>

</body>
</html>

Using my comp time and counting it was roughly 4 seconds. 4 seconds is 6.5-7.5faster then my app. I plan to scan through a thousands of files so taking 3.75hours instead of 30mins would be a big problem. How can i make this code faster? I know someone will say firefox caches the images but i want to say 1) it still needs to check the headers from the remote server to see if it has been updated (which is what i want my app to do) 2) I am not receiving the body, my code should only be requesting the header. So, how do i solve this?

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1 Answer

I noticed that an HttpWebRequest hangs on the first request. I did some research and what seems to be happening is that the request is configuring or auto-detecting proxies. If you set

request.Proxy = null;

on the web request object, you might be able to avoid an initial delay.

With proxy auto-detect:

using (var response = (HttpWebResponse)request.GetResponse()) //6,956 ms
{
}

Without proxy auto-detect:

request.Proxy = null;
using (var response = (HttpWebResponse)request.GetResponse()) //154 ms
{
}

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
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