C#异步Web请求:当所有请求都完成时执行操作
本文关键字：请求 完成时 执行 操作 异步 Web | 更新日期: 2023-09-27 17:57:43
我在C#中有一个基本的抓取控制台应用程序，它异步地使用WebRequest从站点列表中获取html。它工作得很好，但我如何设置一个触发器，当列表中的每个网站都被处理后就会关闭？
我花了几个小时在网上研究各种解决方案，包括MS文档，但没有一个通过代码提供直接的答案。我读过关于IAsyncResult的文章。AsyncWaitHandle，但我不知道如何将它集成到我的代码中。我只想在所有线程完成处理或超时时调用一个自定义函数。
一个技巧是，我永远不知道我的列表中有多少网站（它是用户定义的），所以我需要一个足够强大的解决方案，可以等待5个事件才能完成100000个事件。
谢谢。以下工作代码：
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Net;
using System.Threading;
namespace AsyncApp_01
{
class Program
{
static void Main(string[] args)
{
ArrayList alSites = new ArrayList();
alSites.Add("http://www.google.com");
alSites.Add("http://www.lostspires.com");
ScanSites(alSites);
Console.Read();
}
private static void ScanSites(ArrayList sites)
{
foreach (string uriString in sites)
{
WebRequest request = HttpWebRequest.Create(uriString);
request.Method = "GET";
object data = new object(); //container for our "Stuff"
// RequestState is a custom class to pass info to the callback
RequestState state = new RequestState(request, data, uriString);
IAsyncResult result = request.BeginGetResponse(new AsyncCallback(UpdateItem), state);
//Register the timeout callback
ThreadPool.RegisterWaitForSingleObject(result.AsyncWaitHandle, new WaitOrTimerCallback(ScanTimeoutCallback), state, (30 * 1000), true);
}
}
private static void UpdateItem(IAsyncResult result)
{
// grab the custom state object
RequestState state = (RequestState)result.AsyncState;
WebRequest request = (WebRequest)state.Request;
// get the Response
HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(result);
Stream s = (Stream)response.GetResponseStream();
StreamReader readStream = new StreamReader(s);
// dataString will hold the entire contents of the requested page if we need it.
string dataString = readStream.ReadToEnd();
response.Close();
s.Close();
readStream.Close();
Console.WriteLine(dataString);
}
private static void ScanTimeoutCallback(object state, bool timedOut)
{
if (timedOut)
{
RequestState reqState = (RequestState)state;
if (reqState != null)
{
reqState.Request.Abort();
}
Console.WriteLine("aborted- timeout");
}
}
class RequestState
{
public WebRequest Request; // holds the request
public object Data; // store any data in this
public string SiteUrl; // holds the UrlString to match up results (Database lookup, etc).
public RequestState(WebRequest request, object data, string siteUrl)
{
this.Request = request;
this.Data = data;
this.SiteUrl = siteUrl;
}
}
}
}
任何能告诉我如何限制并发线程数量的人都可以获得额外的积分。例如，如果我有100个站点要处理，我该如何设置它，以便一次处理10个站点，而不是更多。我不想打开100个线程。
这是我整理的一个快速样本。我删除了WebClient实现，因为您似乎在使用WebRequest实现。我也在利用。Net4的ConcurrentBag:
public class Scraper
{
private readonly IEnumerable<string> _sites;
private readonly ConcurrentBag<string> _data;
private volatile int _count;
private readonly int _total;
public Scraper(IEnumerable<string> sites)
{
_sites = sites;
_data = new ConcurrentBag<string>();
_total = sites.Count();
}
public void Start()
{
foreach (var site in _sites)
{
ScrapeSite(site);
}
}
private void ScrapeSite(string site)
{
var req = WebRequest.Create(site);
req.BeginGetResponse(AsyncCallback, req);
}
private void AsyncCallback(IAsyncResult ar)
{
Interlocked.Increment(ref _count);
var req = ar.AsyncState as WebRequest;
var result = req.EndGetResponse(ar);
var reader = new StreamReader(result.GetResponseStream());
var data = reader.ReadToEnd();
this.OnSiteScraped(req.RequestUri.AbsoluteUri, data);
_data.Add(data);
if (_count == _total)
{
OnScrapingComplete();
}
}
private void OnSiteScraped(string site, string data)
{
var handler = this.SiteScraped;
if (handler != null)
{
handler(this, new SiteScrapedEventArgs(site, data));
}
}
private void OnScrapingComplete()
{
var handler = this.ScrapingComplete;
if (handler != null)
{
handler(this, new ScrapingCompletedEventArgs(_data));
}
}
public event EventHandler<SiteScrapedEventArgs> SiteScraped;
public event EventHandler<ScrapingCompletedEventArgs> ScrapingComplete;
}
public class SiteScrapedEventArgs : EventArgs
{
public string Site { get; private set; }
public string Data { get; private set; }
public SiteScrapedEventArgs(string site, string data)
{
this.Site = site;
this.Data = data;
}
}
好吧，我创建了一些基本的类，这应该就可以了。如果这还不够，对不起，我根本帮不了你：
public class RankedPage
{
public int Rank { get; set; }
public string Site { get; set; }
}
public class WebRequestData
{
public WebRequest WebRequest { get; set; }
public RankedPage Page { get; set; }
}
public class Scraper
{
private readonly IEnumerable<RankedPage> _sites;
private readonly ConcurrentBag<KeyValuePair<RankedPage,string>> _data;
private volatile int _count;
private readonly int _total;
public Scraper(IEnumerable<RankedPage> sites)
{
_sites = sites;
_data = new ConcurrentBag<KeyValuePair<RankedPage, string>>();
_total = sites.Count();
}
public void Start()
{
foreach (var site in _sites)
{
ScrapeSite(site);
}
}
private void ScrapeSite(RankedPage site)
{
var req = WebRequest.Create(site.Site);
req.BeginGetResponse(AsyncCallback, new WebRequestData{ Page = site, WebRequest = req});
}
private void AsyncCallback(IAsyncResult ar)
{
Interlocked.Increment(ref _count);
var webRequestData = ar.AsyncState as WebRequestData;
var req = webRequestData.WebRequest;
var result = req.EndGetResponse(ar);
var reader = new StreamReader(result.GetResponseStream());
var data = reader.ReadToEnd();
this.OnSiteScraped(webRequestData.Page, data);
_data.Add(new KeyValuePair<RankedPage, string>(webRequestData.Page,data));
if (_count == _total)
{
OnScrapingComplete();
}
}
private void OnSiteScraped(RankedPage page, string data)
{
var handler = this.SiteScraped;
if (handler != null)
{
handler(this, new SiteScrapedEventArgs(page, data));
}
}
private void OnScrapingComplete()
{
var handler = this.ScrapingComplete;
if (handler != null)
{
handler(this, new ScrapingCompletedEventArgs(_data));
}
}
public event EventHandler<SiteScrapedEventArgs> SiteScraped;
public event EventHandler<ScrapingCompletedEventArgs> ScrapingComplete;
}
public class SiteScrapedEventArgs : EventArgs
{
public RankedPage Site { get; private set; }
public string Data { get; private set; }
public SiteScrapedEventArgs(RankedPage site, string data)
{
this.Site = site;
this.Data = data;
}
}
public class ScrapingCompletedEventArgs : EventArgs
{
public IEnumerable<KeyValuePair<RankedPage,string >> SiteData { get; private set; }
public ScrapingCompletedEventArgs(IEnumerable<KeyValuePair<RankedPage, string>> siteData)
{
this.SiteData = siteData;
}
}