C# Multithreaded Access on Excel File

Question

I'm coding on an multithreaded C# Application which provides some statistics for an Excel File. I opened the File by following Code:

    private static Excel.Application excelApp = new Excel.Application();
    private static Excel.Workbook workbook = excelApp.Workbooks.Open(path);
    private static Excel.Worksheet worksheet = workbook.ActiveSheet;
    private static Excel.Range range = worksheet.UsedRange;
    private static int totalColumns = worksheet.UsedRange.Columns.Count;

To collect the Data out of the columns I'm using one Thread per column.

for (int columnCount = 1; columnCount <= /*range.Columns.Count*/totalColumns; columnCount++)
{
    Thread worker = new Thread(printSpread);
    worker.Start(columnCount);
}

I got HRESULT: 0x800A01A8 Error if I don't start a new Excel Application in each Thread. My question is, do I have to do this or is there an opportunity to use just one Excel Application? I do think, there is a problem in accessing the data from just one Application by mulitple Threads, which would explain the COM Exception. Thanks for your time and help.

Answer 1

you can read excel file like a single table and save data in memory with a simple datatable. So, you can work in multithread after closing the excel file.

sConnection = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Test.xls;Extended Properties=""Excel 12.0;HDR=No;IMEX=1"""
using (var conn = new OleDbConnection(sConnection)
{
    conn.Open();
    string query = "SELECT  * FROM [" + mySheetName + "]";
    var adapter = new OleDbAdapter(query, conn);
    var table = new DataTable();
    adapter.Fill(table);
    //or you can use datareader

    //Now you can close excel and dbConnection
    //and work in memory with datatable and threads
}

Answer 2

Wouldn't it be an option to parse the excell file to a (temporary) database-table, since databases tend to lend theirselves much better to multiple-access situations compared to a simple excell-file on-disk?

Gathering from the fact that your current code mainly seems to count the amount of columns in a row, a simple database could have that data updated on each data-change. Considering that; if you build a good database model, parsing the excell-files would pretty much auto-fill the database with the data you want to use.

This may however be a over-complicated approach as I'm not sure of your actual goals.