ASP.NET Backgroundworkers for spreadsheet creation: multiple ones interfering with each other? - asp.net

Question

I am writing an ASP.NET application in which i need to create multiple excel reports. the report creation is pretty time-consuming (up to ten seconds for each) so i am using backgroundworkers to create them simultaneously.
My code looks a bit like this:
if (condition1)
{
excel_file_name = "TRANSFER";
BackgroundWorker worker_t = new BackgroundWorker();
worker_t.DoWork += new DoWorkEventHandler(DoWork);
worker_t.WorkerReportsProgress = false;
worker_t.WorkerSupportsCancellation = true;
worker_t.RunWorkerCompleted +=
new RunWorkerCompletedEventHandler(WorkerCompleted);
worker_t.RunWorkerAsync(excel_file_name);
}
if (Condition2)
{
excel_file_name = "NEFT";
BackgroundWorker worker_n = new BackgroundWorker();
worker_n.DoWork += new DoWorkEventHandler(DoWork);
worker_n.WorkerReportsProgress = false;
worker_n.WorkerSupportsCancellation = true;
worker_n.RunWorkerCompleted +=
new RunWorkerCompletedEventHandler(WorkerCompleted);
worker_n.RunWorkerAsync(excel_file_name);
}
there are more conditions but i haven't written them, since they are all similar. the only difference is the Excel_File_Name
the DoWork even then calls a class to create the excel files with the given name.
When condition1 and condition2 are both true, Here is the issue:
1. if i run this slowly using breakpoints during debugging, both files (TRANSFER and NEFT) are created.
2. if, however, i run it without breakpoints like a normal application, only the last file (NEFT in this example) is created.
What can be the issue?
Thanks
PS: For further information, here is the important code from the class that creates the excel file:
private static string placeDataInTemplate(string destFilePath, DataRow dr, bool isCoverLetter)
{
int loop = 0;
ExcelNamespace.Application excelApplication = new ExcelNamespace.Application();
ExcelNamespace.Workbook workbook = excelApplication.Workbooks.Open(destFilePath, 0, false, 5,
"", "", true, ExcelNamespace.XlPlatform.xlWindows, "\t", false, false, 0, true, true, false);
ExcelNamespace.Worksheet workSheet = (ExcelNamespace.Worksheet)workbook.Sheets[sheet_no];
try
{
string value;
string replicate;
string replicate_end;
// get data for Place Holders
sDataTable dtPlaceHolderData = getPlaceHolderData(dr);
//make Display Alerts False
excelApplication.DisplayAlerts = false;
if (dtPlaceHolderData != null && dtPlaceHolderData.Rows.Count > 0)
{
int rowCntDt = 0; //Which row will be used for data?
int i = 1;
Excel.Range Find = (ExcelNamespace.Range)workSheet.Cells.Find("#",
(ExcelNamespace.Range)workSheet.Cells[1, 1],
Excel.XlFindLookIn.xlValues,
Excel.XlLookAt.xlPart,
Excel.XlSearchOrder.xlByRows,
Excel.XlSearchDirection.xlNext,
false,
false,
Missing.Value);
while (Find != null && loop <= 200)
{
loop++;
value = Find.Value2.ToString();
if (condition)
//VERY long if...else if
}
string approveDirPath = destFilePath.Replace(Path.GetFileName(destFilePath), string.Empty);
workbook.Close(true, destFilePath, Type.Missing);
excelApplication.Quit();
string filepath = destFilePath.Split('-')[0];
string approval_id = dr[0].ToString();
return destFilePath;
}
return string.Empty;
}
catch (Exception ex)
{
//do something
}
finally
{
//release resources
}
NOTE: I have removed a lot of needless code. I can paste it if needed. Thank you

Answer 1

Most likely cause is some shared state between two threads - shared state may include excel application and workbooks. So you need to inspect your code for the same.
On the side note, instead of using Excel Automation to generate excel files, you may consider using some in-process library which would be perhaps more scalable and void of such issues. Have a look at one such free basic library at code project