Collection was modified; Operation may not execute

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I am creating a program that gets data from serial port then save it on a textfile.
while saving the data on the text file. I simultaneously read the data and create a line graph. but I receive a problem like this..

"Collection was modified; Operation may not execute"

and this

"cannot access the file because it is being used by another program"

on backgroundworker1

VB

Dim ChartValues As StreamReader = New StreamReader(strDATPath)
         While ChartValues.Peek <> -1
             Dim arr() As String = ChartValues.ReadLine.Split(","c)
             If arr.Length = 7 Then
                 Chart1.Series(0).Points.AddXY(arr(0), arr(1))
                 Chart1.Series(1).Points.AddXY(arr(0), arr(2))
                 Chart2.Series(0).Points.AddXY(arr(0), arr(3))
                 Chart2.Series(1).Points.AddXY(arr(0), arr(4))
                 Chart3.Series(0).Points.AddXY(arr(0), arr(5))
                 Chart3.Series(1).Points.AddXY(arr(0), arr(6))
             End If
         End While

on backgroundworker2

VB

SerialPort1.WriteLine(tbMessage.Text)
tbIn.Text = TimeOfDay.ToString("HH:mm:ss") & "," & SerialPort1.ReadLine()

       showdetails()



       'Create directory for the file
       If Not Directory.Exists("C:\SP_Log\" + strDateToday + "\") Then
           Directory.CreateDirectory("C:\SP_Log\" + strDateToday + "\")
       End If

       'Create the file
       If Not File.Exists(strDATPath) Then
           Using swLogWriter As StreamWriter = File.CreateText(strDATPath)
           End Using
       Else
           Using swLogWriter As StreamWriter = File.AppendText(strDATPath)
               If tbIn.Text <> Nothing Then
                   swLogWriter.WriteLine(tbIn.Text)

               End If

           End Using
       End If

on timer tick

VB

If SerialPort1.IsOpen() Then


           '  createlog()
           If BackgroundWorker2.IsBusy = False Then
               counterCurrent = 0
               BackgroundWorker2.RunWorkerAsync()

           End If

           If BackgroundWorker1.IsBusy = False Then
               counterCurrent = 0
               BackgroundWorker1.RunWorkerAsync()

           End If

           'tbIn.Text = ""


       End If

what should be the problem?

Posted 7-Oct-15 22:56pm

NekoNao

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Comments

Tomas Takac 8-Oct-15 5:04am

Where exactly is the first exception thrown ("Collection was modified; Operation may not execute")? Why exactly are you surprised to get the other exception ("cannot access the file because it is being used by another program")? Do you need to write the data into a file?

NekoNao 8-Oct-15 5:31am

Collection was modified error was here ,, Dim ChartValues As StreamReader = New StreamReader(strDATPath)
While ChartValues.Peek <> -1
Dim arr() As String = ChartValues.ReadLine.Split(","c)
If arr.Length = 7 Then
Chart1.Series(0).Points.AddXY(arr(0), arr(1))
Chart1.Series(1).Points.AddXY(arr(0), arr(2))
Chart2.Series(0).Points.AddXY(arr(0), arr(3))
Chart2.Series(1).Points.AddXY(arr(0), arr(4))
Chart3.Series(0).Points.AddXY(arr(0), arr(5))
Chart3.Series(1).Points.AddXY(arr(0), arr(6))
End If
End While

NekoNao 8-Oct-15 5:31am

and the cannot access .. is here

'Create directory for the file
If Not Directory.Exists("C:\SP_Log\" + strDateToday + "\") Then
Directory.CreateDirectory("C:\SP_Log\" + strDateToday + "\")
End If

'Create the file
If Not File.Exists(strDATPath) Then
Using swLogWriter As StreamWriter = File.CreateText(strDATPath)
End Using
Else
Using swLogWriter As StreamWriter = File.AppendText(strDATPath)
If tbIn.Text <> Nothing Then
swLogWriter.WriteLine(tbIn.Text)

End If

End Using
End If

NekoNao 8-Oct-15 5:32am

and yes. i need to always write data on the textfile WHILE getting the data to make a graph. T_T

Tomas Takac 8-Oct-15 6:36am

It seems like an overkill to me to write the data to a file and then read it to display it. Plus you get the locking problem of course. Why not just to display the data once you read it from the serial port and then store it to the file?

NekoNao 8-Oct-15 22:42pm

Thanks! I did not think of that. Ill try it. but what if I want to graph the data on text file first ?

Tomas Takac 9-Oct-15 3:41am

Then you do it like that: read from serial port - write to file - add to the chart. You just need one background worker and take care when updating UI.

NekoNao 9-Oct-15 4:11am

its working! thanks for the logic!

ZurdoDev 8-Oct-15 8:53am

Sounds like you need to try and stop doing it all at once. Read in the data and then process it and don't try to do too much at once.

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Matt T Heffron · Accepted Answer · 2015-10-08T09:09:00

Solution 1

File is a poor choice to communicate between threads (BackgroundWorker).
The System.Collections.Concurrent.BlockingCollection(Of T) is designed for exactly the type of inter-thread communication that you seem to need.

If the file is just for the communication, then drop it entirely.

Posted 8-Oct-15 9:09am

Matt T Heffron

Comments

NekoNao 3-Nov-15 22:36pm

thanks for the answer!