C#特別適合於構造蜘蛛程序，這是因爲它已經內置了HTTP訪問和多線程的能力，而這兩種能力對於蜘蛛程序來說都是非常關鍵的。下面是構造一個蜘蛛程序要解決的關鍵問題：
⑴ HTML分析：需要某種HTML解析器來分析蜘蛛程序遇到的每一個頁面。
⑵ 頁面處理：需要處理每一個下載得到的頁面。下載得到的內容可能要保存到磁盤，或者進一步分析處理。
⑶ 多線程：只有擁有多線程能力，蜘蛛程序才能真正做到高效。
⑷ 確定何時完成：不要小看這個問題，確定任務是否已經完成並不簡單，尤其是在多線程環境下。
一、HTML解析
C#語言本身不包含解析HTML的能力，但支持XML解析；不過，XML有着嚴格的語法，爲XML設計的解析器對 HTML來說根本沒用，因爲HTML的語法要寬鬆得多。爲此，我們需要自己設計一個HTML解析器。本文提供的解析器是高度獨立的，你可以方便地將它用於其它用C#處理HTML的場合。
本文提供的HTML解析器由ParseHTML類實現，使用非常方便：首先創建該類的一個實例，然後將它的Source屬性設置爲要解析的HTML文檔：
ParseHTML parse = new ParseHTML();
parse.Source = "<p>Hello World</p>";
接下來就可以利用循環來檢查HTML文檔包含的所有文本和標記。通常，檢查過程可以從一個測試Eof方法的while循環開始：
while(!parse.Eof())
{
char ch = parse.Parse();
Parse方法將返回HTML文檔包含的字符--它返回的內容只包含那些非HTML標記的字符，如果遇到了HTML標記，Parse方法將返回0值，表示現在遇到了一個HTML標記。遇到一個標記之後，我們可以用GetTag()方法來處理它。
if(ch==0)
{
HTMLTag tag = parse.GetTag();
}
一般地，蜘蛛程序最重要的任務之一就是找出各個HREF屬性，這可以藉助C#的索引功能完成。例如，下面的代碼將提取出HREF屬性的值（如果存在的話）。
Attribute href = tag["HREF"];
string link = href.Value;
獲得Attribute對象之後，通過Attribute.Value可以得到該屬性的值。
二、處理HTML頁面
下面來看看如何處理HTML頁面。首先要做的當然是下載HTML頁面，這可以通過C#提供的HttpWebRequest類實現：
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(m_uri);
response = request.GetResponse();
stream = response.GetResponseStream();
接下來我們就從request創建一個stream流。在執行其他處理之前，我們要先確定該文件是二進制文件還是文本文件，不同的文件類型處理方式也不同。下面的代碼確定該文件是否爲二進制文件。
if( !response.ContentType.ToLower().StartsWith("text/") )
{
SaveBinaryFile(response);
return null;
}
string buffer = "",line;
如果該文件不是文本文件，我們將它作爲二進制文件讀入。如果是文本文件，首先從stream創建一個StreamReader，然後將文本文件的內容一行一行加入緩衝區。
reader = new StreamReader(stream);
while( (line = reader.ReadLine())!=null )
{
buffer+=line+"/r/n";
}
裝入整個文件之後，接着就要把它保存爲文本文件。
SaveTextFile(buffer);
下面來看看這兩類不同文件的存儲方式。
二進制文件的內容類型聲明不以"text/"開頭，蜘蛛程序直接把二進制文件保存到磁盤，不必進行額外的處理，這是因爲二進制文件不包含HTML，因此也不會再有需要蜘蛛程序處理的HTML鏈接。下面是寫入二進制文件的步驟。
首先準備一個緩衝區臨時地保存二進制文件的內容。 byte []buffer = new byte[1024];
接下來要確定文件保存到本地的路徑和名稱。如果要把一個myhost.com網站的內容下載到本地的c:/test文件夾，二進制文件的網上路徑和名稱是，則本地路徑和名稱應當是c:/test/images/logo.gif。與此同時，我們還要確保c:/test目錄下已經創建了images子目錄。這部分任務由convertFilename方法完成。
string filename = convertFilename( response.ResponseUri );
convertFilename方法分離HTTP地址，創建相應的目錄結構。確定了輸出文件的名字和路徑之後就可以打開讀取Web頁面的輸入流、寫入本地文件的輸出流。
Stream outStream = File.Create( filename );
Stream inStream = response.GetResponseStream();
接下來就可以讀取Web文件的內容並寫入到本地文件，這可以通過一個循環方便地完成。
int l;
do
{
l = inStream.Read(buffer,0,
buffer.Length);
if(l>0)
outStream.Write(buffer,0,l);
} while(l>0);
寫入整個文件之後，關閉輸入流、輸出流。
outStream.Close();
inStream.Close();
比較而言，下載文本文件更容易一些。文本文件的內容類型總是以"text/"開頭。假設文件已被下載並保存到了一個字符串，這個字符串可以用來分析網頁包含的鏈接，當然也可以保存爲磁盤上的文件。下面代碼的任務就是保存文本文件。
string filename = convertFilename( m_uri );
StreamWriter outStream = new StreamWriter( filename );
outStream.Write(buffer);
outStream.Close();
在這裏，我們首先打開一個文件輸出流，然後將緩衝區的內容寫入流，最後關閉文件。
三、多線程
多線程使得計算機看起來就象能夠同時執行一個以上的操作，不過，除非計算機包含多個處理器，否則，所謂的同時執行多個操作僅僅是一種模擬出來的效果--靠計算機在多個線程之間快速切換達到"同時"執行多個操作的效果。一般而言，只有在兩種情況下多線程才能事實上提高程序運行的速度。第一種情況是計算機擁有多個處理器，第二種情況是程序經常要等待某個外部事件。
對於蜘蛛程序來說，第二種情況正是它的典型特徵之一，它每發出一個URL請求，總是要等待文件下載完畢，然後再請求下一個URL。如果蜘蛛程序能夠同時請求多個URL，顯然能夠有效地減少總下載時間。
爲此，我們用DocumentWorker類封裝所有下載一個URL的操作。每當一個DocumentWorker的實例被創建，它就進入循環，等待下一個要處理的URL。下面是DocumentWorker的主循環：
while(!m_spider.Quit )
{
m_uri = m_spider.ObtainWork();
m_spider.SpiderDone.WorkerBegin();
string page = GetPage();
if(page!=null)
ProcessPage(page);
m_spider.SpiderDone.WorkerEnd();
}
這個循環將一直運行，直至Quit標記被設置成了true（當用戶點擊"Cancel"按鈕時，Quit標記就被設置成true）。在循環之內，我們調用ObtainWork獲取一個URL。ObtainWork將一直等待，直到有一個URL可用--這要由其他線程解析文檔並尋找鏈接才能獲得。Done類利用WorkerBegin和WorkerEnd方法來確定何時整個下載操作已經完成。
從圖一可以看出，蜘蛛程序允許用戶自己確定要使用的線程數量。在實踐中，線程的最佳數量受許多因素影響。如果你的機器性能較高，或者有兩個處理器，可以設置較多的線程數量；反之，如果網絡帶寬、機器性能有限，設置太多的線程數量其實不一定能夠提高性能。
四、任務完成了嗎？
利用多個線程同時下載文件有效地提高了性能，但也帶來了線程管理方面的問題。其中最複雜的一個問題是：蜘蛛程序何時纔算完成了工作？在這裏我們要藉助一個專用的類Done來判斷。
首先有必要說明一下"完成工作"的具體含義。只有當系統中不存在等待下載的URL，而且所有工作線程都已經結束其處理工作時，蜘蛛程序的工作纔算完成。也就是說，完成工作意味着已經沒有等待下載和正在下載的URL。
Done類提供了一個WaitDone方法，它的功能是一直等待，直到Done對象檢測到蜘蛛程序已完成工作。下面是WaitDone方法的代碼。
public void WaitDone()
{
Monitor.Enter(this);
while ( m_activeThreads>0 )
{
Monitor.Wait(this);
}
Monitor.Exit(this);
}
WaitDone方法將一直等待，直到不再有活動的線程。但必須注意的是，下載開始的最初階段也沒有任何活動的線程，所以很容易造成蜘蛛程序一開始就立即停止的現象。爲解決這個問題，我們還需要另一個方法WaitBegin來等待蜘蛛程序進入"正式的"工作階段。一般的調用次序是：先調用WaitBegin，再接着調用WaitDone，WaitDone將等待蜘蛛程序完成工作。下面是WaitBegin的代碼：
public void WaitBegin()
{
Monitor.Enter(this);
while ( !m_started )
{
Monitor.Wait(this);
}
Monitor.Exit(this);
}
WaitBegin方法將一直等待，直到m_started標記被設置。m_started標記是由 WorkerBegin方法設置的。工作線程在開始處理各個URL之時，會調用WorkerBegin；處理結束時調用WorkerEnd。 WorkerBegin和WorkerEnd這兩個方法幫助Done對象確定當前的工作狀態。下面是WorkerBegin方法的代碼：
public void WorkerBegin()
{
Monitor.Enter(this);
m_activeThreads++;
m_started = true;
Monitor.Pulse(this);
Monitor.Exit(this);
}
WorkerBegin方法首先增加當前活動線程的數量，接着設置m_started標記，最後調用Pulse方法以通知（可能存在的）等待工作線程啓動的線程。如前所述，可能等待Done對象的方法是WaitBegin方法。每處理完一個URL，WorkerEnd方法會被調用：
public void WorkerEnd()
{
Monitor.Enter(this);
m_activeThreads--;
Monitor.Pulse(this);
Monitor.Exit(this);
}
WorkerEnd方法減小m_activeThreads活動線程計數器，調用Pulse釋放可能在等待Done對象的線程--如前所述，可能在等待Done對象的方法是WaitDone方法。
結束語：本文介紹了開發Internet蜘蛛程序的基礎知識，上面提供的源代碼將幫助你進一步深入理解本文的主題。這裏提供的代碼非常靈活，你可以方便地將它用於自己的程序。
DocumentWorker.cs
using System;
using System.Net;
using System.IO;
using System.Threading;
namespace Spider
{
/// <summary>
/// Perform all of the work of a single thread for the spider.
/// This involves waiting for a URL to becomve available, download
/// and then processing the page.
///
/// </summary>
// 完成必須由單個工作線程執行的操作，包括
// 等待可用的URL，下載和處理頁面
public class DocumentWorker
{
/// <summary>
/// The base URI that is to be spidered.
/// </summary>
// 要掃描的基礎URI
private Uri m_uri;
/// <summary>
/// The spider that this thread "works for"
/// </summary>
//
private Spider m_spider;
/// <summary>
/// The thread that is being used.
/// </summary>
private Thread m_thread;
/// <summary>
/// The thread number, used to identify this worker.
/// </summary>
// 線程編號，用來標識當前的工作線程
private int m_number;
/// <summary>
/// The name for default documents.
/// </summary>
// 缺省文檔的名字
public const string IndexFile = "index.html";
/// <summary>
/// Constructor.
/// </summary>
/// <param name="spider">The spider that owns this worker.</param>
// 構造函數，參數表示擁有當前工作線程的蜘蛛程序
public DocumentWorker(Spider spider)
{
m_spider = spider;
}
/// <summary>
/// This method will take a URI name, such ash /images/blank.gif
/// and convert it into the name of a file for local storage.
/// If the directory structure to hold this file does not exist, it
/// will be created by this method.
/// </summary>
/// <param name="uri">The URI of the file about to be stored</param>
/// <returns></returns>
// 輸入參數是一個URI名稱，例如/images/blank.gif.
// 把它轉換成本地文件名稱。如果尚未創建相應的目錄
// 結構，則創建之
private string convertFilename(Uri uri)
{
string result = m_spider.OutputPath;
int index1;
int index2;
// add ending slash if needed
if( result[result.Length-1]!='//' )
result = result+"//";
// strip the query if needed
String path = uri.PathAndQuery;
int queryIndex = path.IndexOf("?");
if( queryIndex!=-1 )
path = path.Substring(0,queryIndex);
// see if an ending / is missing from a directory only
int lastSlash = path.LastIndexOf('/');
int lastDot = path.LastIndexOf('.');
if( path[path.Length-1]!='/' )
{
if(lastSlash>lastDot)
path+="/"+IndexFile;
}
// determine actual filename
lastSlash = path.LastIndexOf('/');
string filename = "";
if(lastSlash!=-1)
{
filename=path.Substring(1+lastSlash);
path = path.Substring(0,1+lastSlash);
if(filename.Equals("") )
filename=IndexFile;
}
// 必要時創建目錄結構
index1 = 1;
do
{
index2 = path.IndexOf('/',index1);
if(index2!=-1)
{
String dirpart = path.Substring(index1,index2-index1);
result+=dirpart;
result+="//";
Directory.CreateDirectory(result);
index1 = index2+1;
}
} while(index2!=-1);
// attach name
result+=filename;
return result;
}
/// <summary>
/// Save a binary file to disk.
/// </summary>
/// <param name="response">The response used to save the file</param>
// 將二進制文件保存到磁盤
private void SaveBinaryFile(WebResponse response)
{
byte []buffer = new byte[1024];
if( m_spider.OutputPath==null )
return;
string filename = convertFilename( response.ResponseUri );
Stream outStream = File.Create( filename );
Stream inStream = response.GetResponseStream();
int l;
do
{
l = inStream.Read(buffer,0,buffer.Length);
if(l>0)
outStream.Write(buffer,0,l);
}
while(l>0);
outStream.Close();
inStream.Close();
}
/// <summary>
/// Save a text file.
/// </summary>
/// <param name="buffer">The text to save</param>
// 保存文本文件
private void SaveTextFile(string buffer)
{
if( m_spider.OutputPath==null )
return;
string filename = convertFilename( m_uri );
StreamWriter outStream = new StreamWriter( filename );
outStream.Write(buffer);
outStream.Close();
}
/// <summary>
/// Download a page
/// </summary>
/// <returns>The data downloaded from the page</returns>
// 下載一個頁面
private string GetPage()
{
WebResponse response = null;
Stream stream = null;
StreamReader reader = null;
try
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(m_uri);
response = request.GetResponse();
stream = response.GetResponseStream();
if( !response.ContentType.ToLower().StartsWith("text/") )
{
SaveBinaryFile(response);
return null;
}
string buffer = "",line;
reader = new StreamReader(stream);
while( (line = reader.ReadLine())!=null )
{
buffer+=line+"/r/n";
}
SaveTextFile(buffer);
return buffer;
}
catch(WebException e)
{
System.Console.WriteLine("下載失敗，錯誤：" + e);
return null;
}
catch(IOException e)
{
System.Console.WriteLine("下載失敗，錯誤：" + e);
return null;
}
finally
{
if( reader!=null ) reader.Close();
if( stream!=null ) stream.Close();
if( response!=null ) response.Close();
}
}
/// <summary>
/// Process each link encountered. The link will be recorded
/// for later spidering if it is an http or https docuent,
/// has not been visited before(determined by spider class),
/// and is in the same host as the original base URL.
/// </summary>
/// <param name="link">The URL to process</param>
private void ProcessLink(string link)
{
Uri url;
// fully expand this URL if it was a relative link
try
{
url = new Uri(m_uri,link,false);
}
catch(UriFormatException e)
{
System.Console.WriteLine( "Invalid URI:" + link +" Error:" + e.Message);
return;
}
if(!url.Scheme.ToLower().Equals("http") &&
!url.Scheme.ToLower().Equals("https") )
return;
// comment out this line if you would like to spider
// the whole Internet (yeah right, but it will try)
if( !url.Host.ToLower().Equals( m_uri.Host.ToLower() ) )
return;
//System.Console.WriteLine( "Queue:"+url );
m_spider.addURI( url );
}
/// <summary>
/// Process a URL
/// </summary>
/// <param name="page">the URL to process</param>
private void ProcessPage(string page)
{
ParseHTML parse = new ParseHTML();
parse.Source = page;
while(!parse.Eof())
{
char ch = parse.Parse();
if(ch==0)
{
Attribute a = parse.GetTag()["HREF"];
if( a!=null )
ProcessLink(a.Value);
a = parse.GetTag()["SRC"];
if( a!=null )
ProcessLink(a.Value);
}
}
}
/// <summary>
/// This method is the main loop for the spider threads.
/// This method will wait for URL's to become available,
/// and then process them.
/// </summary>
public void Process()
{
while(!m_spider.Quit )
{
m_uri = m_spider.ObtainWork();
m_spider.SpiderDone.WorkerBegin();
System.Console.WriteLine("Download("+this.Number+"):"+m_uri);
string page = GetPage();
if(page!=null)
ProcessPage(page);
m_spider.SpiderDone.WorkerEnd();
}
}
/// <summary>
/// Start the thread.
/// </summary>
public void start()
{
ThreadStart ts = new ThreadStart( this.Process );
m_thread = new Thread(ts);
m_thread.Start();
}
/// <summary>
/// The thread number. Used only to identify this thread.
/// </summary>
public int Number
{
get
{
return m_number;
}
set
{
m_number = value;
}
}
}
}
Done.cs
using System;
using System.Threading;
namespace Spider
{
/// <summary>
/// This is a very simple object that
/// allows the spider to determine when
/// it is done. This object implements
/// a simple lock that the spider class
/// can wait on to determine completion.
/// Done is defined as the spider having
/// no more work to complete.
///
/// This spider is copyright 2003 by Jeff Heaton. However, it is
/// released under a Limited GNU Public License (LGPL). You may
/// use it freely in your own programs. For the latest version visit
/// http://www.jeffheaton.com.
///
/// </summary>
public class Done
{
/// <summary>
/// The number of SpiderWorker object
/// threads that are currently working
/// on something.
/// </summary>
private int m_activeThreads = 0;
/// <summary>
/// This boolean keeps track of if
/// the very first thread has started
/// or not. This prevents this object
/// from falsely reporting that the spider
/// is done, just because the first thread
/// has not yet started.
/// </summary>
private bool m_started = false;
/// <summary>
/// This method can be called to block
/// the current thread until the spider
/// is done.
/// </summary>
public void WaitDone()
{
Monitor.Enter(this);
while ( m_activeThreads>0 )
{
Monitor.Wait(this);
}
Monitor.Exit(this);
}
/// <summary>
/// Called to wait for the first thread to
/// start. Once this method returns the
/// spidering process has begun.
/// </summary>
public void WaitBegin()
{
Monitor.Enter(this);
while ( !m_started )
{
Monitor.Wait(this);
}
Monitor.Exit(this);
}
/// <summary>
/// Called by a SpiderWorker object
/// to indicate that it has begun
/// working on a workload.
/// </summary>
public void WorkerBegin()
{
Monitor.Enter(this);
m_activeThreads++;
m_started = true;
Monitor.Pulse(this);
Monitor.Exit(this);
}
/// <summary>
/// Called by a SpiderWorker object to
/// indicate that it has completed a
/// workload.
/// </summary>
public void WorkerEnd()
{
Monitor.Enter(this);
m_activeThreads--;
Monitor.Pulse(this);
Monitor.Exit(this);
}
/// <summary>
/// Called to reset this object to
/// its initial state.
/// </summary>
public void Reset()
{
Monitor.Enter(this);
m_activeThreads = 0;
Monitor.Exit(this);
}
}
}
ParseHTML.cs
using System;
namespace Spider
{
/// <summary>
/// Summary description for ParseHTML.
///
/// This spider is copyright 2003 by Jeff Heaton. However, it is
/// released under a Limited GNU Public License (LGPL). You may
/// use it freely in your own programs. For the latest version visit
/// http://www.jeffheaton.com.
///
/// </summary>
public class ParseHTML:Parse
{
public AttributeList GetTag()
{
AttributeList tag = new AttributeList();
tag.Name = m_tag;
foreach(Attribute x in List)
{
tag.Add((Attribute)x.Clone());
}
return tag;
}
public String BuildTag()
{
String buffer="<";
buffer+=m_tag;
int i=0;
while ( this[i]!=null )
{// has attributes
buffer+=" ";
if ( this[i].Value == null )
{
if ( this[i].Delim!=0 )
buffer+=this[i].Delim;
buffer+=this[i].Name;
if ( this[i].Delim!=0 )
buffer+=this[i].Delim;
}
else
{
buffer+=this[i].Name;
if ( this[i].Value!=null )
{
buffer+="=";
if ( this[i].Delim!=0 )
buffer+=this[i].Delim;
buffer+=this[i].Value;
if ( this[i].Delim!=0 )
buffer+=this[i].Delim;
}
}
i++;
}
buffer+=">";
return buffer;
}
protected void ParseTag()
{
m_tag="";
Clear();
// Is it a comment?
if ( (GetCurrentChar()=='!') &&
(GetCurrentChar(1)=='-')&&
(GetCurrentChar(2)=='-') )
{
while ( !Eof() )
{
if ( (GetCurrentChar()=='-') &&
(GetCurrentChar(1)=='-')&&
(GetCurrentChar(2)=='>') )
break;
if ( GetCurrentChar()!='/r' )
m_tag+=GetCurrentChar();
Advance();
}
m_tag+="--";
Advance();
Advance();
Advance();
ParseDelim = (char)0;
return;
}
// Find the tag name
while ( !Eof() )
{
if ( IsWhiteSpace(GetCurrentChar()) || (GetCurrentChar()=='>') )
break;
m_tag+=GetCurrentChar();
Advance();
}
EatWhiteSpace();
// Get the attributes
while ( GetCurrentChar()!='>' )
{
ParseName = "";
ParseValue = "";
ParseDelim = (char)0;
ParseAttributeName();
if ( GetCurrentChar()=='>' )
{
AddAttribute();
break;
}
// Get the value(if any)
ParseAttributeValue();
AddAttribute();
}
Advance();
}
public char Parse()
{
if( GetCurrentChar()=='<' )
{
Advance();
char ch=char.ToUpper(GetCurrentChar());
if ( (ch>='A') && (ch<='Z') || (ch=='!') || (ch=='/') )
{
ParseTag();
return (char)0;
}
else return(AdvanceCurrentChar());
}
else return(AdvanceCurrentChar());
}
}
}
Spider.cs
using System;
using System.Collections;
using System.Net;
using System.IO;
using System.Threading;
namespace Spider
{
/// <summary>
/// The main class for the spider. This spider can be used with the
/// SpiderForm form that has been provided. The spider is completely
/// selfcontained. If you would like to use the spider with your own
/// application just remove the references to m_spiderForm from this file.
///
/// The files needed for the spider are:
///
/// Attribute.cs - Used by the HTML parser
/// AttributeList.cs - Used by the HTML parser
/// DocumentWorker - Used to "thread" the spider
/// Done.cs - Allows the spider to know when it is done
/// Parse.cs - Used by the HTML parser
/// ParseHTML.cs - The HTML parser
/// Spider.cs - This file
/// SpiderForm.cs - Demo of how to use the spider
///
/// This spider is copyright 2003 by Jeff Heaton. However, it is
/// released under a Limited GNU Public License (LGPL). You may
/// use it freely in your own programs. For the latest version visit
/// http://www.jeffheaton.com.
///
/// </summary>
public class Spider
{
/// <summary>
/// The URL's that have already been processed.
/// </summary>
private Hashtable m_already;
/// <summary>
/// URL's that are waiting to be processed.
/// </summary>
private Queue m_workload;
/// <summary>
/// The first URL to spider. All other URL's must have the
/// same hostname as this URL.
/// </summary>
private Uri m_base;
/// <summary>
/// The directory to save the spider output to.
/// </summary>
private string m_outputPath;
/// <summary>
/// The form that the spider will report its
/// progress to.
/// </summary>
private SpiderForm m_spiderForm;
/// <summary>
/// How many URL's has the spider processed.
/// </summary>
private int m_urlCount = 0;
/// <summary>
/// When did the spider start working
/// </summary>
private long m_startTime = 0;
/// <summary>
/// Used to keep track of when the spider might be done.
/// </summary>
private Done m_done = new Done();
/// <summary>
/// Used to tell the spider to quit.
/// </summary>
private bool m_quit;
/// <summary>
/// The status for each URL that was processed.
/// </summary>
enum Status { STATUS_FAILED, STATUS_SUCCESS, STATUS_QUEUED };
/// <summary>
/// The constructor
/// </summary>
public Spider()
{
reset();
}
/// <summary>
/// Call to reset from a previous run of the spider
/// </summary>
public void reset()
{
m_already = new Hashtable();
m_workload = new Queue();
m_quit = false;
}
/// <summary>
/// Add the specified URL to the list of URI's to spider.
/// This is usually only used by the spider, itself, as
/// new URL's are found.
/// </summary>
/// <param name="uri">The URI to add</param>
public void addURI(Uri uri)
{
Monitor.Enter(this);
if( !m_already.Contains(uri) )
{
m_already.Add(uri,Status.STATUS_QUEUED);
m_workload.Enqueue(uri);
}
Monitor.Pulse(this);
Monitor.Exit(this);
}
/// <summary>
/// The URI that is to be spidered
/// </summary>
public Uri BaseURI
{
get
{
return m_base;
}
set
{
m_base = value;
}
}
/// <summary>
/// The local directory to save the spidered files to
/// </summary>
public string OutputPath
{
get
{
return m_outputPath;
}
set
{
m_outputPath = value;
}
}
/// <summary>
/// The object that the spider reports its
/// results to.
/// </summary>
public SpiderForm ReportTo
{
get
{
return m_spiderForm;
}
set
{
m_spiderForm = value;
}
}
/// <summary>
/// Set to true to request the spider to quit.
/// </summary>
public bool Quit
{
get
{
return m_quit;
}
set
{
m_quit = value;
}
}
/// <summary>
/// Used to determine if the spider is done,
/// this object is usually only used internally
/// by the spider.
/// </summary>
public Done SpiderDone
{
get
{
return m_done;
}
}
/// <summary>
/// Called by the worker threads to obtain a URL to
/// to process.
/// </summary>
/// <returns>The next URL to process.</returns>
public Uri ObtainWork()
{
Monitor.Enter(this);
while(m_workload.Count<1)
{
Monitor.Wait(this);
}
Uri next = (Uri)m_workload.Dequeue();
if(m_spiderForm!=null)
{
m_spiderForm.SetLastURL(next.ToString());
m_spiderForm.SetProcessedCount(""+(m_urlCount++));
long etime = (System.DateTime.Now.Ticks-m_startTime)/10000000L;
long urls = (etime==0)?0:m_urlCount/etime;
m_spiderForm.SetElapsedTime( etime/60 + " minutes (" + urls +" urls/sec)" );
}
Monitor.Exit(this);
return next;
}
/// <summary>
/// Start the spider.
/// </summary>
/// <param name="baseURI">The base URI to spider</param>
/// <param name="threads">The number of threads to use</param>
public void Start(Uri baseURI,int threads)
{
// init the spider
m_quit = false;
m_base = baseURI;
addURI(m_base);
m_startTime = System.DateTime.Now.Ticks;;
m_done.Reset();
// startup the threads
for(int i=1;i<threads;i++)
{
DocumentWorker worker = new DocumentWorker(this);
worker.Number = i;
worker.start();
}
// now wait to be done
m_done.WaitBegin();
m_done.WaitDone();
}
}
}