Question

I am not familiar with multithreading. Image I have a method to do some intensive search on a string, and return 2 lists of integers as out parameters.

public static void CalcModel(string s, out List<int> startPos, out List<int> len)
    {
        // Do some intensive search
    }

The search on long string is very time consuming. So I want to split the string into several fragments, search with multithreads, and recombine the result (adjust the startPos accordingly).

How to integrate multithreading in this kinda process? Thanks

I forgot to mention the following two things:

1. I want to set a string length cutoff, and let the code to decide how many fragments it needs.
2. I had a hard time to associate the startPos of each fragments (on the original string) with the thread. How can I do that?

Answer 1

Rather than get too bogged down in details, generally, you send each thread a “return object.” Once you’ve started all the threads, you block on them and wait until they are all finished.

While each thread is running, the thread modifies its work object and terminates when it has produced the output.

So roughly this (I can’t tell exactly how you want to split it up, so perhaps you can modify this):

public class WorkItem {
    public string InputString;
    public List<int> startPos;
    public List<int> len;
}

public static void CalcLotsOfStrings(string s, out List<int> startPos, out List<int> len)
{
    WorkItem wi1 = new WorkItem();
    wi1.InputString = s;
    Thread t1 = new Thread(InternalCalcThread1);
    t1.Start(wi1);
    WorkItem wi2 = new WorkItem();
    wi2.InputString = s;
    Thread t2 = new Thread(InternalCalcThread2);
    t2.Start(wi2);

    // You can now wait for the threads to complete or start new threads
    // When you're done, wi1 and wi2 will be filled with the updated data
    // but make sure not to use them until the threads are done!
}


public static void InternalCalcThread1(object item)
{
    WorkItem w = item as WorkItem;
    w.startPos = new List<int>();
    w.len = new List<int>();

    // Do work here - populate the work item data
}


public static void InternalCalcThread2(object item)
{
    // Do work here
}