Error stop Http Listener

George_George

Hello everyone, Here is my simple application code for a Windows Service application. The question is, when stop the service, there is always, // [System.InvalidOperationException] = {"Please call the Start() method before calling this method."} Does anyone have any ideas why there is such issue and how to fix?

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.ServiceProcess;
using System.Text;
using System.Net;
using System.Threading;

namespace TestServiceStop1
{
public partial class Service1 : ServiceBase
{
private Thread _tHttpThread;
private TestHttpServer _server;

    public Service1()
    {
        InitializeComponent();
    }

    protected override void OnStart(string\[\] args)
    {
        \_server = new TestHttpServer(this);

        \_tHttpThread = new Thread(\_server.StartListen);

        \_tHttpThread.Start();
    }

    protected override void OnStop()
    {
        // stop HTTP server
        \_server.Stop(false);
    }
}

public class TestHttpServer
{
    // listening HTTP port
    private int \_Port = 0;

    // internal wrapped HTTP listener
    private HttpListener \_Server = new HttpListener();

    private Service1 \_manager;

    public TestHttpServer (Service1 manager)
    {
        \_manager = manager;
    }

    public int ListenPort
    {
        get
        {
            return \_Port;
        }
        set
        {
            \_Port = value;
        }
    }

    public void StartListen()
    {
        try
        {
            IAsyncResult result;
            \_Server.Prefixes.Add(String.Format("http://+:{0}/", 9099));
            \_Server.Start();
            while (true)
            {
                result = \_Server.BeginGetContext(new AsyncCallback(this.HttpCallback), \_Server);
                result.AsyncWaitHandle.WaitOne();
            }
        }
        // any exceptions are not expected
        // catch InvalidOperationException during service stop
        // \[System.InvalidOperationException\] = {"Please call the Start() method before calling this method."}
        catch (Exception ex)
        {
            throw ex;
        }
    }

N a v a n e e t h

George_George wrote:

_Server.Stop();

I can't find where you are stopping the thread. You are just stopping the HTTPListener, not the thread. OnStop() method should be able to exit the thread also, I guess. Not sure this will be the reason for error.

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GDavy

George_George wrote:

while (true) { result = _Server.BeginGetContext(new AsyncCallback(this.HttpCallback), _Server); result.AsyncWaitHandle.WaitOne(); }

In your StartListen you get in this endless loop. So after stopping the server the call to

_Server.BeginGetContext(new AsyncCallback(this.HttpCallback), _Server);

most likely throws this exception. You will need to check if the _Server object is still active before calling the BeginGetContext I guess...

George_George

Thanks GDavy, How do check whether _Server is still active? Any suggestions? :-) regards, George

George_George

Sorry N a v a n e e t h, My English is not very good. You mean I need to stop the thread tHttpThread in OnStop? regards, George

N a v a n e e t h

George_George wrote:

You mean I need to stop the thread tHttpThread in OnStop?

Yes. The thread is not stopping in your code. Stop that on OnStop() method.

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George_George

Thanks N a v a n e e t h, How to stop the thread gracefully? I think of using Abort, but we have discussed before this method call is not a good idea always. regards, George

GDavy

from MSDN on the BeginGetContext call[^] The InvalidOperationException is thrown when the server is stopped. So there you go it is normal behaviour. You can check the IsListening Property to see if the _Server is started or not.

GDavy

Actually because the BeginGetContext call will throw an exception when the _Server object is stopped, the thread will stop too so no extra work is actually required.

N a v a n e e t h

I mean the thread which he created.

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N a v a n e e t h

Go with this[^]. It will work.

All C# applications should call Application.Quit(); in the beginning to avoid any .NET problems.- Unclyclopedia How to use google | Ask smart questions

GDavy

;) I know which thread you mean. The thread he creates uses the StartListening Function. In that function the BeginGetContext call is made, and this will throw the InvalidOperationException when the _Server object is stopped. So the thread he creates really does exit when the _Server stops. He will just need to catch the InvalidOperationException and evaluate that it is expected behaviour.

George_George

Thanks GDavy, Your solution works. Cool! regards, George

George_George

Thanks GDavy! If I fixed in this way, are there any need to stop the tHttpThread thread?

            while (true)
            {
                if (\_Server.IsListening)
                {
                    result = \_Server.BeginGetContext(new AsyncCallback(this.HttpCallback), \_server);
                    result.AsyncWaitHandle.WaitOne();
                }
                else
                {
                    break;
                }
            }

regards, George

N a v a n e e t h

GDavy wrote:

In that function the BeginGetContext call is made, and this will throw the InvalidOperationException when the _Server object is stopped. So the thread he creates really does exit when the _Server stops. He will just need to catch the InvalidOperationException

I know. I was suggesting him to stop that thread when HTTPListener stops, so it won't call again BeginGetContext(). Will that be a good method than catching exception, and thread getting aborted automatically ?

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Zoltan Balazs

George_George wrote:

catch (Exception ex) { throw ex; }

You're not doing anything with the exception and then you throw a modified exception (without the original stack trace). If you want to re-throw the original exception use

throw;

Simple.

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George_George

Thanks Zoltan, Good to learn from you. Any comments to? http://www.codeproject.com/script/Forums/View.aspx?fid=1649&msg=2580309[^] regards, George

George_George

Thanks N a v a n e e t h, 1. Sounds good. Could you show the code please? I want to learn from you but feel do not know how to code. :-) 2. Any comments to? http://www.codeproject.com/script/Forums/View.aspx?fid=1649&msg=2580309[^] regards, George

N a v a n e e t h

1 -

volatile bool continue = true;
public void StartListen()
{
try
{
IAsyncResult result;
_Server.Prefixes.Add(String.Format("http://+:{0}/", 9099));
_Server.Start();
while (continue)
{
result = _Server.BeginGetContext(new AsyncCallback(this.HttpCallback), _Server);
result.AsyncWaitHandle.WaitOne();
}
}
// any exceptions are not expected
// catch InvalidOperationException during service stop
// [System.InvalidOperationException] = {"Please call the Start() method before calling this method."}
catch (Exception ex)
{
throw ex;
}
}

    public void Stop(bool isTerminate)
    {
        **continue = false;**
        \_Server.Stop();
    }

2 - It looks fine.

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George_George

Thanks N a v a n e e t h, I think your code has an issue when we are executing result = _Server.BeginGetContext(new AsyncCallback(this.HttpCallback), _Server) while at the same time, Stop is called. :-) In this situation, there is no chance to check continue status variable. Any comments? regards, George