MultiThreading c# message exchanger, PulseAll problem

[Bassem]

Hello,
I'm trying to do an ASP.NET message-exchanger (littel messenger).
I chose a long scenario; using JavaScript not to reload the page by requesting another page "CommPage.aspx" that implements C# methods, Implementing the famous reader/writer problem using Monitors. As this:
1) on page load a receive request occurs to "CommPage.aspx", on "CommPage.aspx" a reader thread start.
2) on button click a send request to "CommPage.aspx" occurs, then a writer thread start.
3) Reader thread:

        Monitor.Enter(_myRoom);
        Monitor.Wait(_myRoom);
        Monitor.Exit(_myRoom);

Then read a property that contain the message (string). Then send a receive request again (Circulation).
4) Writer thread:
First set a property message

        Monitor.Enter(this);
 
        /// rarely happen when more than one request to write arrive to
        /// server at the same time.
        if (_writer)
            Monitor.Wait(this);
 
        _writer = true;
 
        _writer = false;
        Monitor.PulseAll(this);
        Monitor.Exit(this);
        try { Thread.CurrentThread.Abort(); }   catch { }

I view more than one page in browser to test.
The problem is when a send request occurs only the first loaded page has a receive response. with another send request the second loaded page has get receive response. Then the third ..... .

It seems to me like Monitor.PulseAll acts like Monitor.Pulse.
Please What I'm wrong about?

Any help, Thanks.

[Bassem]

I'm sorry maybe I didn't declare my problem well.
I'm trying to create chatting rooms where more than one instant client can entre. And for each client can entre more than one chatting room simultaneously.
It is a simple design two web pages (Default.aspx, CommPage.aspx) and two classes (Groups, ChattingRoom).
1) Default.aspx : my main page I do some DHTML (changes on client-side) so I use JavaScript to do whatever I want.
On page load send a receive-request to CommPage.aspx with group name

 function page_load()
{
    /// on load request for new data
    receiveData("g1");
}
 function receiveData(group)
{
    if(null==xmlHttpReceiver)
    {
        alert("Your browser does not support AJAX!");
        return;
    }
 
    var url="CommPage.aspx";
    url=url+"?way=receive"+"&group="+group;
 
    xmlHttpReceiver.onreadystatechange=receiverStateChanged;
    xmlHttpReceiver.open("GET",url,true);
    xmlHttpReceiver.send(null);
}
 function receiverStateChanged() 
{ 
    if (xmlHttpReceiver.readyState==4)
    { 
        document.getElementById("Text2").value = xmlHttpReceiver.responseText + "\r\n";
 
        /// after receiving request to receive again;
        /// circulation
        receiveData("g1");
    }
} 

On button click send a send-request to CommPage.aspx with group name and user name and message (all are strings).

 function Button2_onclick() {
 
    var mess = document.getElementById('Text1').value;
    document.getElementById("Text1").value="";
    sendData("g1","u1",mess);
}
 function sendData(group, user, message)
{
    if (message.length==0)
      { 
          return;
      }
    if (xmlHttpSender==null)
      {
          alert ("Your browser does not support AJAX!");
          return;
      } 
    var url="CommPage.aspx";
    url=url+"?way=send"+"&message="+message+"&user="+user+"&group="+group;
 
    xmlHttpSender.onreadystatechange=senderStateChanged;
    xmlHttpSender.open("GET",url,true); // POST 
    xmlHttpSender.send(null);
}

2) CommPage.aspx: executes c# methods.
on Page_Load verify the request either send or receive request

 public partial class Default2 : System.Web.UI.Page
{
    Groups _groups = Groups.Instance;
    ChatRoom _myRoom;
 
    protected void Page_Load(object sender, EventArgs e)
    {
        Response.Expires = -1;
 
        if ("receive" == Request.QueryString["way"])
            ReceiveRequested();
        else
            SendRequested();
    }
 
    private void SendRequested()
    {
        _myRoom = _groups.MyRoom(Request.QueryString["group"]);
        string groupName = Request.QueryString["group"];
        string userName = Request.QueryString["user"];
        string message = Request.QueryString["message"];
 
 
        //try then catch null reference and redirect to custom error page, so that'll happend only
        // if this page is requested directly and no parameters are set.
 
        _myRoom.NewMessageContent = userName + " says :" + message + Environment.NewLine;
        Thread writer = new Thread(new ThreadStart(Write));
        writer.Start();
    }
 
    private void ReceiveRequested()
    {
        _myRoom = _groups.MyRoom(Request.QueryString["group"]);
 
        Read();
        Response.Write(_myRoom.AllConversation);
    }
 
    public void Read()
    {
        Monitor.Enter(_myRoom);
        Monitor.Wait(_myRoom);
        Monitor.Exit(_myRoom);
    }
 
    public void Write()
    {
        Monitor.Enter(_myRoom);
 
        /// rarely happend when more than one request to write arrive to
        /// server at the same time.
        if (_myRoom._writer)
            Monitor.Wait(_myRoom);
 
        _myRoom._writer = true;
 
        _myRoom._allText += _myRoom.NewMessageContent;
 
        _myRoom._writer = false;
        Monitor.PulseAll(_myRoom);
        Monitor.Exit(_myRoom);
        try { Thread.CurrentThread.Abort(); }
        catch { }
    }
}

Readers only wait until a writer pulse all of them.
3) Group class : is shared among all classes that reference it (singleton)

 public class Groups
{
    static readonly Groups _groups = new Groups();
    List<ChatRoom> _rooms = new List<ChatRoom>(); 
    bool editor;
 
    private Groups()
    {
 
    }
 
    public ChatRoom EnterChat(string roomName, string userName)
    {
        Monitor.Enter(this);
 
        if (editor)
            Monitor.Wait(this);
        editor = true;
 
        foreach (ChatRoom room in _rooms)
        {
            if (room.Name == roomName)
            {
                editor = false;
                Monitor.PulseAll(this);
                Monitor.Exit(this);
                return room;            
            }
        }
 
        ChatRoom newRoom = new ChatRoom(roomName);
        _rooms.Add(newRoom);
 
        editor = false;
        Monitor.PulseAll(this);
        Monitor.Exit(this);
        return newRoom;                 
    }
 
    public ChatRoom MyRoom(string roomName)
    {
        foreach (ChatRoom room in _rooms)
            if (room.Name == roomName)
                return room;
        return null;
    }
 
    public static Groups Instance
    {
        get { return _groups; }
    }
}

4) ChattRoom class : contains only string to save the conversation.

 public class ChatRoom
{
    readonly string _name;
 
    public string _allText = string.Empty;
    public string _newMessage;
 
    public bool _writer;
 
    public ChatRoom(string name)
    {
        _name = name;
        }
 
    public string NewMessageContent
    {
        set { _newMessage = value; }
        get { return _newMessage; }
    }
 
    public string Name
    {
        get { return _name; }
    }
 
    public string AllConversation
    {
        get { return _allText; }
    }
} 

Everything works fine but when a writer PulseAll waiting threads (Readers) only one thread notified and response.

Please any help! Any idea!
Thanks in advanced.

[Frinavale]

Hmm I'm not sure how much help I'm going to be because I haven't done much threading stuff before (mainly just used it in school...and in load capacity testing).

I looked up the PulseAll method. It says the following:

The thread that currently owns the lock on the specified object invokes this method to signal all threads waiting to acquire the lock on the object. After the signal is sent, the waiting threads are moved to the ready queue. When the thread that invoked PulseAll releases the lock, the next thread in the ready queue acquires the lock.

It seems to me that the PulseAll method is doing exactly what it is supposed to: a thread locks the Object, does something and gets a response from the Object, then the next thread is able to gain a lock. This would mean that only 1 thread would get the response.

Maybe the PulseAll method isn't the method you should be using.
Consider researching the other methods available to you to find one that does suit your needs.

-Frinny

[Bassem]

Thanks Frinny, I think you did help me much.
How come I forgot that using Monitor and lock, allow only one thread to acquire the lock on a particular object until it releases it and threads in waitsleepjoin should be pulsed before. But only one thread working in the critical part of code at a time.

I tried to use Monitor.Suspend() and Monitor.Resume() but they are decade cuz of some problems they have.

I converted to ManualResetEvent works but I'm trying to set a condition that threads should WaitOne() on it.

Your words enlightened me thanks again and again.
Bassem