Re: Threaded Proxy? - C# Discussion Boards

Vishwanath Patil12-Nov-09 2:37

Vishwanath Patil

12-Nov-09 2:37

super answer, works without prob.
Thanks Smile | :)

Dave Kreskowiak12-Nov-09 4:23

Dave Kreskowiak

12-Nov-09 4:23

I'm making a few assumptions on what you're doing and why you're saving the image of a fingerprint in your database, so...

It may work, but what are you really getting?? I don't know anything about the control you're using, but, is the image being "snapshotted" from the PictureBox at the native resolution of the conrol?? My bet is probably not. So, what you're taking a snapshot of is a lossy, scaled version of the data making up the fingerprint. You're not saving the full resolution of the fingerprint image in the database.

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008
But no longer in 2009...

Vishwanath Patil12-Nov-09 18:04

Vishwanath Patil

12-Nov-09 18:04

I do agree your point, client wants finger print image to be printed on glossy paper. One more thing! I made picturebox autosize, I may not loose resolution/data(am not sure about it). Important thing is finger print here not for maching.

Thank you

Dave Kreskowiak13-Nov-09 15:15

Dave Kreskowiak

13-Nov-09 15:15

Scaling up a screen shot image to a printed image will result is "jaggies". You'll get a much lower quality output on the printer. Unless, of course, your printed image is the size of a postage stamp...

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008
But no longer in 2009...

Threaded Proxy?

joana.simoes12-Nov-09 0:40

joana.simoes

12-Nov-09 0:40

Hi,
Thanks for reading this!
For the people who never read any of my posts I am trying to write a proxy server in c#.
I am trying to "keep it simple" and stay away from asynchronous requests, but is not possible to totally avoid threading and I think I am encountering some multi threading problems.

The idea is to have a listener socket, binded to a certain prefix. Whatever requests I get there, I append them the correct credentials and send them straight to the (atuthenticated) server on the other side; then I grabb the bytes of the response and show them in the browser. For this I am using the HttpListenerContext class.

public void Start()
{
    try
    {
        m_listener.Start();
        while (true)
        {
            try
            {
                HttpListenerContext request = m_listener.GetContext();
                ThreadPool.QueueUserWorkItem(ProcessRequest, request);
            }
            catch (Exception e)
            {
                System.Diagnostics.Debug.WriteLine(e.ToString());
            }
        }
    }
    catch (Exception e)
    {
        System.Diagnostics.Debug.WriteLine(e.ToString());
    }
    System.Diagnostics.Debug.WriteLine("Listening socket on port " + m_port);
}

The function ProcessRequest does the actual job that I wanted. (note that it does it in an asynchronous way!)

private void ProcessRequest(object listenerContext)
{
    try
    {
        var context = (HttpListenerContext)listenerContext;

        try
        {
            // READ ADDRESS HERE...
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(address);

            Stream instream = context.Request.InputStream;
            Stream outstream = response.GetResponseStream();

            //TRANSFER DATA FROM REQUEST STREAM TO RESPONSE STREAM
            // Close streams
            instream.Close();
            outstream.Close();
            context.Response.OutputStream.Close();
        }
        catch (Exception ex)
        {

        }
    }
    catch
    {
        Restart();
    }
}

Normally, everything goes ok; however, whenever I have a client that does a lot of requests very quickly (almost parallely) there is a problem in line writing the output stream (with the bytes that I just grabbed from the server) and an error is thrown:

An operation was attempted on a nonexistent network connection

This is misterious; is the network connection referring to the incoming stream (the server that I am comunicating with)? if its there is no apparent problem, because I checked and the connection is still on... or is this connection referring to the output stream? if it is, there is also no apparent problem cause I checked it with the functon [i]CanWrite[/i] and it returns true, so it is looks in good health;
If anybody has any "light" to to bring into this question I would really appreciate it, cause I googled it to exhaustion and did not come to any conclusions Confused | :confused:

Anyway, moving on: I caught the error and figure out that I need to somehow close the streams that are opened; I did not find a clean easy way to do it (cause I cannot access the streams anymore), so the "brute-force" approach was to close the actual listener and start it again (so that I can again listen for connections);

private void Restart()
{
    Stop();
    Start();
}

Most of the times, this is ok, but sometimes, when I enter the [i]Start()[/i] function, there is a problem with this line:

HttpListenerContext request = m_listener.GetContext();

and an exception is thrown:

The I/O operation has been aborted because of either a thread exit or an application request

and then I am in a bit of a mess.
Apart from trying to solve this particular errors that cause my application to fail requests once in a while, I am looking at the bigger picture and wondering if the issues I am encountering are from not approaching properly the situation; am I having simultaneous access to the code and no handling properly the multithreading (I actually tried a lock() of the critical section without any improvement...) ? do I need multithreading here? or is it something else?
As I said, any help here would be much appreciated! Thanks in advance Thumbs Up | :thumbsup:

Covean12-Nov-09 2:08

Covean

12-Nov-09 2:08

Hi there, I'm not the lightbringer but I have an idea where the problem can be.

try
{
    HttpListenerContext request = m_listener.GetContext();
    ThreadPool.QueueUserWorkItem(ProcessRequest, request);
}
catch (Exception e)
{
    System.Diagnostics.Debug.WriteLine(e.ToString());
}

"HttpListenerContext request = " is an variable thats scope starts with the { after the
try and end with the } before catch. So its only valid within this scope, after this scope
the garbgage collector can decide when it will dispose it (should be an object of generation zero).
So I think you should assure your context lives longer.

Greetings
Covean

Luc Pattyn12-Nov-09 2:23

Luc Pattyn

12-Nov-09 2:23

Hi,

I don't think so. request is passed to QueueUserWorkItem which is bound to store it somewhere (in the TP queue) hence it will stay alive until executed.

Smile | :)

Luc Pattyn

I only read code that is properly indented, and rendered in a non-proportional font; hint: use PRE tags in forum messages

Covean12-Nov-09 2:47

Covean

12-Nov-09 2:47

Yes you seems to be right I tested it, and it really lives as long as the thread lives. However
I run in exactly this problem someday where the gc killed thread objects, which I had to force to be
at least an object with a mid-ranged lifetime-cycle otherwise the app chrashed after a while.
So I thought this can be a reason, but it wasn't. Laugh | :laugh:

To your solution: I only worked one time with ThreadPools, after that I loved it to do this on my own.

[edit] did some typo

Greetings
Covean

Luc Pattyn12-Nov-09 2:22

Luc Pattyn

12-Nov-09 2:22

Hi,

I think your problem is in using the ThreadPool.

The TP holds a large number of threads, and has a queue into which you can insert jobs. Now those jobs get executed by some number of TP threads; however that number does not equal the number of available jobs: it starts of at a few only, and will grow and shrink using a complex algorithm. In one of my experiments I noted it only grows at a rate of 2 per second. Therefore your jobs will queue up and wait on others to finish first, which is not what a normal server does (it either accepts the job or refuses it, but never postpones it).

So IMO you should use either real Threads or (more unlikely to succeed) use asynchronous operations. BackgroundWorkers would not help as they run on the TP as well.

Smile | :)

Luc Pattyn

I only read code that is properly indented, and rendered in a non-proportional font; hint: use PRE tags in forum messages

Santhosh Sebastian Mattathil

joana.simoes13-Nov-09 5:22

joana.simoes

13-Nov-09 5:22

Ok, thanks a lot all for your answers.
So I think the summary of the situation concerning multithreading in C# is (correct me if I'm wrong):
- use asynchronous requests and let the system handle the multithreading; (1)
- use threadPool and let the system handle the multitreading (distribute tasks among worker threads); (2)
- implement "real" multi threading, handling synchronization, locks, etc; (3)

I wanted to keep it as simple as possible, without having to write a lot of "thread" of code (unless absolutely necessary), so I tried to stick to option (2), which as Luc Pattyn mentioned, has some limitations but I think I can "live" with them (that is, the app fails sometimes, I can catch the errors and carry on without major implications for the user).

One thing that I amended in my code, was removing the "restart" of the listener on the event of an exception; there is no need to stop and start the listener on error, and in fact, when I had a lot of threads running, the "restart" of the listener itself was a cause of problems...

The I/O operation has been aborted because of either a thread exit or an application request

So, after refactoring my "ProcessRequest" callback, it now looks like this: no restart of the listener and separate handling of different types of exceptions; one important thing is to close the Context.Response after an error, so that it sends a response to the client;

private void ProcessRequest(object listenerContext)
 {
     try
     {
         byte[] buffer;
         var context = (HttpListenerContext)listenerContext;

         try
         {
             //Make necessary replacements in the host name
             Uri aUri = context.Request.Url;
             string url = aUri.AbsolutePath + aUri.Query;

             System.Uri uri = m_service.GetUri();
             string address = uri.Scheme + "://" + uri.Host + ":" + uri.Port + url;

             // Build Request
             HttpWebRequest request = (HttpWebRequest)WebRequest.Create(address);

             //DO STUFF

             // Close streams
             instream.Close();
             outstream.Close();
             context.Response.OutputStream.Close();
         }

         catch (System.ArgumentException ex)
         {
             context.Response.StatusCode = int.Parse(ex.Message);
             context.Response.StatusDescription = GetStatusDescription(context.Response.StatusCode);

             byte[] buff = System.Text.Encoding.UTF8.GetBytes("<HTML><BODY><b>Proxy Failure:</b> (" +
                 context.Response.StatusCode + ") " + context.Response.StatusDescription + "</HTML></BODY>");

             context.Response.ContentLength64 = buff.Length;
             context.Response.OutputStream.Write(buff, 0, buff.Length);
         }
         catch (System.Net.HttpListenerException ex) { }
         catch (System.Net.WebException ex)
         {
             int status = (int)((HttpWebResponse)ex.Response).StatusCode;

             context.Response.StatusCode = status;
             context.Response.StatusDescription = GetStatusDescription(status);

             context.Response.Close();
         }
         catch (Exception ex) { }//Default
     }
     catch (Exception ex)
     {
         System.Diagnostics.Debug.WriteLine(ex.Message);
         // It should not come here! Are we having troubles closing the stream?
     }
 }

It's not the best solution, has it fails to deliver some jobs (not properly handling the multithreading), but its kind of working and is simple.
cheers,
Jo

PDF conversion

Santhosh Sebastian Mattathil11-Nov-09 23:34

11-Nov-09 23:34

Hai all

I would like to know how i can convert office 2003(.doc) to pdf using some open source library dll's. I was successful in converting office 2007 files to pdf. I used different opensource dlls like itextsharp,sharppdf etc... but they wont take any .doc files for conversion. We can only create an entirely new pdf document out of it.

Friends any help is greatly appreciated...

I was behind it for quite amount of time

Thnx n advance...

Santo

Santhosh

Showing non 96dpi jpegs in PictureBox

Chesnokov Yuriy11-Nov-09 23:00

Chesnokov Yuriy

11-Nov-09 23:00

I display some jpeg images loaded from Stream object in dynamicly created PictureBox component.

void function(Strean jpegStream)
{
Bitmap img = new Bitmap(jpegStream);
//attach the img to PictureBox control, created dynalically in advance
}

While 96dpi images are displayed correctly, some of the non 96dpi jpegs, e.g. 72dpi, 480dpi which come from photoshop or digital cameras get corrupted after I attach them to Image property of the PictureBox component and they are displayed.

As though half of the jpeg or more were not decompressed, leaving bottom half of the image grayish.

However if I delete and create again PictureBox component, and attach the same Bitmap object img again, already created from jpeg stream, they are correctly displayed???

Чесноков

Re: Showing non 96dpi jpegs in PictureBox

Eduard Keilholz11-Nov-09 23:03

Eduard Keilholz

11-Nov-09 23:03

Erhm, it seems there's no problem with the dpi's but more with the files itself. Your JPEG compression may be corrupt or something, but I would say the JPEG compression method is not great.

.: I love it when a plan comes together :.
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Loading app.config from a remote location fails to load section handler.

Larantz11-Nov-09 22:57

Re: Loading app.config from a remote location fails to load section handler.

11-Nov-09 22:57

Hi guys.

We're trying to implement a centralized configuration for all .net applications and by so we have created a master configuration at a specific location. We're then creating a custom configuration manager that uses both the local app.config and the centralized master configuration.

The master configuration is read using System.Configuration.ConfigurationManager.OpenMappedExeConfiguration(string path, UserLevel level).
The appSettings section and all other custom sections are read and available but our problem occurs when we try to read the sections from the master configuration using ConfigurationManager.GetSection(string sectionName).

We get a TypeLoadException no matter what type of section handlers we use - .NET handlers or custom handlers, and the method returns a System.Configuration.DefaultSection object instead of the intended type.

Could not load type 'System.Configuration.NameValueSectionHandler' from assembly 'System.Configuration, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.

Reading the same sections from the app.config of the exectuable produces no errors.

Anybody with some ideas as to what causes the problem?

-Larantz

for those about to code, we salute you
Please refer to the Forum Guidelines for appropriate posting.

Shameel11-Nov-09 23:38

Shameel

11-Nov-09 23:38

The type System.Configuration.NameValueSectionHandler is in the System.Configuration namespace but it is actually defined in System.dll and not System.Configuration.dll as you might assume, so change your configuration section to

<section name="" type="System.Configuration.NameValueSectionHandler, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>

and it should work.

Re: Loading app.config from a remote location fails to load section handler.

Larantz11-Nov-09 23:40

Re: Loading app.config from a remote location fails to load section handler.

11-Nov-09 23:40

I'll try that.
Thanks for the tip. Smile | :)

-Larantz

for those about to code, we salute you
Please refer to the Forum Guidelines for appropriate posting.

Larantz11-Nov-09 23:50

Re: Loading app.config from a remote location fails to load section handler.

11-Nov-09 23:50

It seems that the section handler did load so the TypeLoadException is gone.
But instead of actually returning a NameValueCollection - it still just returns a System.Configuration.DefaultSection which is useless.
I just can't get my head around why this is occurring.
It's the same for custom section handlers.

-Larantz

for those about to code, we salute you
Please refer to the Forum Guidelines for appropriate posting.

Shameel12-Nov-09 0:00

Shameel

12-Nov-09 0:00

You might find this useful

http://www.eggheadcafe.com/software/aspnet/30832856/backwards-compatibility-o.aspx[^]

Re: Loading app.config from a remote location fails to load section handler.

Larantz12-Nov-09 0:11