Speed up loop using multithreading in C# (Question)

Question

Imagine I have an function which goes through one million/billion strings and checks smth in them.

f.ex:

foreach (String item in ListOfStrings)
{
            


        

Answer 1

You need to split up the work you want to do in parallel. Here is an example of how you can split the work in two:

List work = (some list with lots of strings)

// Split the work in two
List odd = new List();
List even = new List();
for (int i = 0; i < work.Count; i++)
{
    if (i % 2 == 0)
    {
        even.Add(work[i]);
    }
    else
    {
        odd.Add(work[i]);
    }
}

// Set up to worker delegates
List oddResult = new List();
Action oddWork = delegate { foreach (string item in odd) oddResult.Add(CalculateSmth(item)); };

List evenResult = new List();
Action evenWork = delegate { foreach (string item in even) evenResult.Add(CalculateSmth(item)); };

// Run two delegates asynchronously
IAsyncResult evenHandle = evenWork.BeginInvoke(null, null);
IAsyncResult oddHandle = oddWork.BeginInvoke(null, null);

// Wait for both to finish
evenWork.EndInvoke(evenHandle);
oddWork.EndInvoke(oddHandle);

// Merge the results from the two jobs
List allResults = new List();
allResults.AddRange(oddResult);
allResults.AddRange(evenResult);

return allResults;