Stringbuilder.tostring() throws exception

Question

5.00/5 (1 vote)

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Hello,

I am trying to create an application in which 2-4 threads gets data from different sources
and I have to show that data on my Form in a textbox.
I have taken a stringbuilder and i keep appending the data from different threads into it.
Also a timer with interval of 2 seconds, and on its tick event the whole stringbuilder data
is copied to the textbox. and after a particular length of stringbuilder (lets say) 50000, I clear it.

But sometimes I get this exception :

Message : Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: chunkLength
TargetSite : System.String ToString()

I have searched and found somethings relative
http://social.msdn.microsoft.com/Forums/ar/netfxbcl/thread/1051ec1c-667f-4568-a528-027cb12c34f9

But i am not getting Textbox.Dispatcher.

Now I am not sure what should I do, and also i am not clear why this exception occurs.

Code :

C#

private void clock_Tick(object sender, EventArgs e)
 {
   try
   {
     txtMsg.Text = myClass.myStringBuilder.ToString();  //throws exception sometime
                
      if (myClass.myStringBuilder.Length == 50000)
      {
         myClass.myStringBuilder.Clear();
      }
   }
    catch (Exception ex)
    {
      //create error log
    }
 }

Thanks.

Posted 27-Feb-12 2:35am

DeepsMann

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Comments

ZurdoDev 27-Feb-12 8:40am

Index was out of range error means you are doing something in your class to try and access something that isn't there. If you don't share your code, how can we help?

El_Codero 27-Feb-12 8:46am

Does it work if you check Length of myStringBuilder.Lenght >=50000 && myStringBuilder.Length != null) ?

2 solutions

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Not Active · Accepted Answer · 2012-02-27T03:07:00

Solution 1

With multi-threaded applications you need to actively take steps to synchronize your threads and data access. Since you are adding to and reading from the stringbuilder from multiple threads it could be in any state at any time.

Try something like this

public void AddString(string s)
{
  lock(this.LockObject)
  {
     StringBuilder.Add(s);
  }
}

Posted 27-Feb-12 3:07am

Not Active

Comments

fjdiewornncalwe 27-Feb-12 10:04am

Naturally. +5.

DeepsMann 28-Feb-12 0:41am

Thanks Mark..
got it... :)

Amund Gjersøe · Accepted Answer · 2012-02-27T03:15:00

Using 2-4 threads and thread pooling, it is easy to stumble upon some resource conflicts. Remember to lock your StringBuilder whenever you access it.

Here are some tips if you've never used it:
Remember to distribute the same instance of your lock-token to all threads. The lock-token is just any object, like:

C#

object _myLockToken = new object();

Your code will then be something like:

C#

private void clock_Tick(object sender, EventArgs e)
{
  lock(_myLockToken)
  {
   try
   {
     txtMsg.Text = myClass.myStringBuilder.ToString();  //throws exception sometime
                
      if (myClass.myStringBuilder.Length == 50000)
      {
         myClass.myStringBuilder.Clear();
      }
   }
    catch (Exception ex)
    {
      //create error log
    }
  }
}

lock Statement (C# Reference)

I'm quite confident that this will help.
(Remember the BeginInvoke-pattern when updating the GUI)