Question

Originally,I am using foreach to do my task.
However, I would like to improve the efficiency of the task.
So, I want to use Parallel.ForEach to do my task.

However, error “Object reference not set to an instance occurred.” happened.

Here’s my code:

System.Threading.Tasks.Parallel.ForEach(items, item =>
        {
             System.Threading.Tasks.Parallel.ForEach(item.a, amount =>
                    {
                         WriteToCsv(file, amount.columna, count);
                          count++;
                     });

         });

If I used foreach(var item in items) and foreach (amount in item.a), the code works fine.

Did I miss something for the Parallel.ForEach method?

Answer 1

Why would you want to do this in parallel? You are appending values to a file, and that is a serial (i.e., non-parallel) process.

If you just use a regular foreach, you’ll be fine.