Showing non 96dpi jpegs in PictureBox - C# Discussion Boards

joana.simoes12-Nov-09 0:40

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:

Re: Threaded Proxy?

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

Re: Threaded Proxy?

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

Re: Threaded Proxy?

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

Re: Threaded Proxy?

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

Re: Threaded Proxy?

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

Santhosh Sebastian Mattathil

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 :.
http://www.zonderpunt.nl

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

Larantz11-Nov-09 22:57

Larantz

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.

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

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

Larantz

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.

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

Larantz11-Nov-09 23:50

Larantz

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.

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

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

Larantz

12-Nov-09 0:11

Well that sure answers it.
I'll have a look at the document mentioned there.
Thanks mate!

-Larantz

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

add row to data grid view problem

Rinad11-Nov-09 22:51

Rinad

11-Nov-09 22:51

Hi all

I Want To Add row to data grid view
but I Have a Problem
When I Create a DataGridViewRow row=new DataGridViewRow();

and I Set The Row From Grid1 To row
and The Add it To Grid2

But The VS2008 Give Me this Exception

Row provided already belongs to a DataGridView control.

what is the Problem ??
who can Solve it ??

thanks Rose | [Rose]

Message Closed

11-Nov-09 22:55

stancrm

11-Nov-09 22:55

Message Closed

modified 23-Nov-14 7:03am.

Re: add row to data grid view problem

Rinad11-Nov-09 23:31

Rinad

11-Nov-09 23:31

This is my code,, i create another row bust stell having the same problem !! Frown | :(

private void GridOne_DoubleClick(object sender, EventArgs e)
{

DataGridViewRow row = new DataGridViewRow();
row = GridOne.Rows[GridOne.CurrentRow.Index];

DataGridViewRow row2 = new DataGridViewRow();
row2 = row;
GridTwo.Rows.Add(row2);
}

i stell get this exception !!
Row provided already belongs to a DataGridView control.

Re: add row to data grid view problem

Gerry Schmitz12-Nov-09 1:39

Gerry Schmitz

12-Nov-09 1:39

All you're doing is moving around references and clobbering others.

Read up on the DataGridViewRow.Clone method; which includes an example on how to copy a row and its cell values.

Re: add row to data grid view problem

Luc Pattyn12-Nov-09 2:34

Luc Pattyn

12-Nov-09 2:34

Rinad wrote:
DataGridViewRow row = new DataGridViewRow();
row = GridOne.Rows[GridOne.CurrentRow.Index];

DataGridViewRow row2 = new DataGridViewRow();
row2 = row;

So this is what you're doing:

row = new DataGridViewRow();                   // create a new row (will never be used)
row = GridOne.Rows[GridOne.CurrentRow.Index];  // get reference to row from GridOne

DataGridViewRow row2 = new DataGridViewRow();  // create a new row (will never be used)
row2 = row;                                    // copy reference to row from GridOne

the new rows you create are thrown away in the next line!

For copying a DGV row to another DGV what you probably need (I've never done this) is:
1. get the source row
2. clone it
3. add the clone to DGV2

For moving a DGV row to another DGV what you probably need is:
1. get the source row
2. remove it from DGV1
3. add the clone to DGV2

In both cases, there is no new DataGridViewRow() involved (it wouldn't even now how your row is supposed to look).

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

Inheritence

sris 42611-Nov-09 22:27

sris 426

11-Nov-09 22:27

Dear all,

I have one base class say BaseOne in that I have 2 methods.One method should not be override by the other method.How can i achive this.

Thanks,
Srinivas Mateti

Re: Inheritence

The Man from U.N.C.L.E.11-Nov-09 22:38

The Man from U.N.C.L.E.

11-Nov-09 22:38

I assume you mean that one method can be overridden and the other cannot, as you cannot override a method in the same class. Nothing can stop anyone overloading the method however.
On that assumption mark the overridable method as Virtual and the not overridable one as sealed.

If you have knowledge, let others light their candles at it.
Margaret Fuller (1810 - 1850)
www.JacksonSoft.co.uk

Re: Inheritence

sris 42611-Nov-09 22:59

sris 426

11-Nov-09 22:59

I am extreamly sorry..one method can be override by the child class and the other method should not be override the child class...

Please see the correction and sorry for the mistake.

Thanks,
Srinivas Mateti

Re: Inheritence

dan!sh 11-Nov-09 23:09

dan!sh

11-Nov-09 23:09

Mark the method you want to override as virtual. And do not mark the other.

Like:

public virtual void OverridableMethod();
public void NonOverridableMethod();

It's not necessary to be so stupid, either, but people manage it. - Christian Graus, 2009 AD

Re: Inheritence

sris 42611-Nov-09 23:14

sris 426

11-Nov-09 23:14

Thanks for the reply...so from your reply what i understood is

1) Virtual methods should be override by the child class,if the child class doest implement the virtual methods then error will shown up.
2) And only virtual methods can be override by the child class non virual methods can not be implemented by child class

One more q:
Can I again declare virtual method as virtual in child class???

Thanks in advance,
Srinivas Mateti

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