Can I use multithreading while adding data to datarow in datatable in C# ?

I would use a SemaphoreSlim. This is a class that 'gates' the number of concurrent reads of a database to a preset level. Once that level has been reach, an existing read has to finish before a new read is allowed to start.

//A method to asynchronously load data from the database
private async Task<Order> LoadOrderFromDbAsync(int orderId){//....}
 private SemaphoreSlim semaphoreSlim;
 private async Task<List<Order>> GatedConcurrentLoadOfOrdersAsync(IEnumerable<int> orderIds)
        {
           using (semaphoreSlim = new SemaphoreSlim(maxConcurrencyLevel))
          {
            var tasks = new List<Task<Order>>();
            foreach (int orderId in orderIds)
            {
                //start each task off but don't await it
                //tasks are started by simply invoking the async method
                Task<Order> task = GatedLoadOrderFromDatabaseAsync(orderId);
                tasks.Add(task);
            }

            //await them all to complete
            Order[] loadedOrders = await Task.WhenAll(tasks);
            return loadedOrders.ToList();
         }
        }

 private async Task<Order> GatedLoadOrderFromDatabaseAsync(int orderId)
        {
            //queue here if max number of threads are already active
            await semaphoreSlim.WaitAsync();
           try
            {
              return  await LoadOrderFromDbAsync(orderId);
                
            }
            finally
            {
                //open the gate to let a queued thread run
                semaphoreSlim.Release();
            }
        }

While ADDING rows to a DataTable? Not really.

From the MSDN documentation on the DataTable:

Quote:

This type is safe for multithreaded read operations. You must synchronize any write operations.

While it is possible to use multiple threads to add records to a DataTable object, adding rows to a DataTable must be synchronized. This means that only one thread can add a DataRow to the table at a time, essentially turning the operation into a single threaded operation. You will get little to no performance benefit from using multiple threads.

The real question should be why are you adding so many rows to a DataTable object in the first place? Chances are good you don't need all of those rows in the DataTable.