How do I...read a csv file when parallelly it is updated by some h/w ?

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Hi,

I have csv file which is constantly appended by some hardware controller.
This csv I have to stream it in Datagrid.

I have done streaming on timer, which is working fine. Timer time is set to 1 seconds.

so whats is happening that, the file written by hardware/controller can be in milliseconds or seconds...etc.

my program reads csv after every 1 seconds....and if the time overlaps of reading(from s/w) and writing(from h/w)...then exception comes and program cant read further.

Can any body help me ?

Posted 15-Jan-14 0:03am

Pdeveloper

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OriginalGriff · Answer 1 · 2014-01-15T00:08:00

Solution 1

Use a try...catch block around the access code to pick up the "File In Use" Exception, and if it fails abandon and try again a second later.

C#

try
   {
   ...
   }
catch (IOException ex)

Posted 15-Jan-14 0:08am

OriginalGriff

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Pdeveloper 15-Jan-14 6:18am

I have done this also..when it is in try-catch block and if the file is not use in that second...it reads file and again if while reading the file is in use with h/w.. then this does not work :(

OriginalGriff 15-Jan-14 6:21am

"does not work" in what way?

Pdeveloper 15-Jan-14 6:21am

no..

Pdeveloper 15-Jan-14 6:27am

here is my code

public DataSet LoadCSVToGrid()
{
DataSet ds = new DataSet();

if (File.Exists( @"C:\\Count_06.csv"))
{
try
{
// Creates and opens an ODBC connection
string strConnString = "Driver={Microsoft Text Driver (*.txt; *.csv)};Dbq=" + dirCSV.Trim() +";Extensions=asc,csv,tab,txt; Persist Security Info= false";
string sql_select;
OdbcConnection conn;
conn = new OdbcConnection(strConnString.Trim());
conn.Open();

//Creates the select command text

sql_select = "select * from [" + fileNaneCSV + "]";

//Creates the data adapter
OdbcDataAdapter obj_oledb_da = new OdbcDataAdapter(sql_select, conn);

//Fills dataset with the records from CSV file
obj_oledb_da.Fill(ds, "csv");
DataTable dt = new DataTable();
dt = ds.Tables["csv"];
for (int i = 0; i <= dt.Rows.Count - 1; i++)
{
string temp = dt.Rows[i][0].ToString();
}
//closes the connection
conn.Close();
}
catch (Exception e) //Error
{
MessageBox.Show(e.Message, "Error - LoadCSV", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}
else
{
MessageBox.Show("The csv File does not exists");
}
return ds;
}

AND then this dataset is passed to datagrid.

OriginalGriff 15-Jan-14 6:54am

Ah! You aren't reading the CSV yourself, you are getting SQL to do it...so you won't get an IOException, you will get an SqlException instead. - you could trap that, but I'd copy the CSV in my C#, and pass the copied file to SQL - that way SQL Server can always access the file, and it's your program that is responsible for getting it when it's free.

Mind you, I wouldn't use SQL to access the file anyway - there are quicker, easier solutions to reading CSV data:
http://www.codeproject.com/Articles/9258/A-Fast-CSV-Reader

BillWoodruff 15-Jan-14 8:00am

+5 Excellent sleuthing, as usual. This scenario is way outside my area of experience, but I wonder if there is any way that the OP could "lock" the file in code, so that whatever else is updating it pauses ?

OriginalGriff 15-Jan-14 8:16am

Probably not - he says it's a hardware controller, so there is a good chance that if he does he could lose data. Hence the "copy the file first" option - that or rename it if the hardware creates it each time.

Pdeveloper 16-Jan-14 0:08am

thanks @OriginalGriff !! I got what u want to say, but even i use IO exception or sql server, OR even if I make a copy of file and then use that copied file...still the error comes, its becoz while copying also if h/w writes to original file, it wont work and will say that the file is in use..

Actually I cnt control h/w time. It continuously puts data into file. there is no fixed interval for h/w. So, how cn I parallel read the data irrespective of h/w write time.

I can set my time interval for reading(for ex 1seconds...2seconds), But I dont have any control over h/w.

do u have some idea how can I do this ?

OriginalGriff 16-Jan-14 1:51am

Silly question: does the hardware create the file if it doesn't exist?
If it does, then use a try...catch block and inside it, rename the file. If the rename works, use the newly named file. If it doesn't, try ain, either three or four times, or a second later.
Rename is a much, much faster operation than copy, so you shouldn't affect the hardware too much and you should get problems less often.

You can't open a file if another process (on this case your hardware) has it open for writing - that process has acquired an "exclusive lock" on the file to prevent others affecting it while it writes.