Multi - threading C#

Mark Hughes

HI,
I'm trying to create an ArrayList of array's created by the code below. Each line in the ArrayList requires the previous line's array to calculate. However for each line the code below is run 6 times creating 6 arrays which are merged together and added to the Master ArrayList.
Running this piece of code 6 times for each line is time consuming. Therefore I would like to run the code on seperate threads and when finished merge the 6 arrays together and add them to the ArrayList.
Could somebody please help me with this?
Thanks,
Mark
        public double[, , , ,] PeriodTree()
        {
            // My code creates a double using Previous Period numbers and returns double[, , , ,] ThisPeriod
            double[, , , ,] ThisPeriod = new double[2, 2, 7, 51, 51];
            mycode...
            return ThisPeriod;
         }

4 Replies

Know the answer? Post it — somebody with the same question will find it here.

jinge17y ago
Accepted answer
Hi friend,

Not using threads correctly will cause bad performance. You know that when you create a new thread, a kernal object will be created and a context switch will happened, all these are expansive operation.

If the work is very short, then we don't need to use multiple threads.
Otherwise, I think APM pattern is situable in your case. You can run the work in the threadpool. Please refer to the following article.

http://msdn.microsoft.com/en-us/magazine/cc164139.aspx
There is one thing not mentioned in that article, actually we can also use Delegate.BeginInvoke to call a method asyc..

If you have any problem, please let me know.
Mark Hughes17y ago
Thanks jinge, thats what I needed to do
Mark Hughes17y ago
Thanks jinge.
However I had used this method previousley and it resulted in my code running slower because I had to re-create the threads numerous times.
My piece of code does not take a long time to run but it does have to be called alot of times throughout the main procedure. For example:
My Main peice of code does the following:
private ArrayList GetResults()
        {
            double[, , , ,] ThisPeriod = new double[2, 2, 7, 51, 51];
            ArrayList InterimPeriods = new ArrayList();
            ArrayList MatchPeriods = new ArrayList();
            ThisPeriod[0, 0, 0, 0, 0] = 0.5;
            ThisPeriod[1, 0, 0, 0, 0] = 0.5;
            MatchPeriods.Add(ThisPeriod); //here I add period 1 to my MathPeriods ArrayList (this is the starting point)
            // I now look to calculate the rest of the Array based on Period1 and a set of parameters which are not important for this example.
            for (int t = 1; t < 721; t++)
            {
                double[, , , ,] RollingPeriod = new double[2, 2, 7, 51, 51];
                double[, , , ,] PassPreviousPeriod = (double[, , , ,])MatchPeriods[t - 1];
                this.createCalculationTrees(t, PassPreviousPeriod); //this is a seprate piece of code that creates 6 instances of a class based on the PreviousPeriod Array values. They are named ctPeriod1, ctPeriod2 etc.
                ctPeriod1.RunThisThread();
                ctPeriod2.RunThisThread();
                ctPeriod3.RunThisThread();
                ctPeriod4.RunThisThread();
                ctPeriod5.RunThisThread();
                ctPeriod6.RunThisThread(); //These 6 lines will run the code to fill the PeriodTree and return in each instance a results array called Interim period which is then added to the ArrayList below. **This is the part I want to multi-thread**
                InterimPeriods.Add(ctPeriod1.InterimPeriod);
                InterimPeriods.Add(ctPeriod2.InterimPeriod);
                InterimPeriods.Add(ctPeriod3.InterimPeriod);
                InterimPeriods.Add(ctPeriod4.InterimPeriod);
                InterimPeriods.Add(ctPeriod5.InterimPeriod);
                InterimPeriods.Add(ctPeriod6.InterimPeriod);
//After this point these six arrays are merged together and added to the MatchPeriods ArrayList
merging...
MatchPeriods.Add(RollingPeriod);
}
What I did try was to create 6 threads each time it looped to the part of my code I wanted multi threaded. I started the 6 threads and placed a piece of code which locked the InterimPeriod Array until the code had run. Once all InterimPeriod Arrays were unlocked I merged the six added them to MatchPeriods and looped for the next period. However this resulted in my code running slower and I believe this was due to the re-creation of the Threads on each loop. Is there a better way to do this?
Thanks

jinge17y ago

If we take Backgroundworker component which .net framwork provides, it would be easier, and here is an article.

You can also use the following code to run the method in a different thread:

 

Thread t = new Thread(new ThreadStart(callbackmethod));
t.Start();

If you need to pass the parameter to the callbackmethoed, then you will use :

From msdn:

 

 using System;
using System.Threading;

public class Work
{
    public static void Main()
    {
        // To start a thread using a shared thread procedure, use
        // the class name and method name when you create the 
        // ParameterizedThreadStart delegate. C# infers the 
        // appropriate delegate creation syntax:
        //    new ParameterizedThreadStart(Work.DoWork)
        //
        Thread newThread = new Thread(Work.DoWork);

        // Use the overload of the Start method that has a
        // parameter of type Object. You can create an object that
        // contains several pieces of data, or you can pass any 
        // reference type or value type. The following code passes
        // the integer value 42.
        //
        newThread.Start(42);

        // To start a thread using an instance method for the thread 
        // procedure, use the instance variable and method name when 
        // you create the ParameterizedThreadStart delegate. C# infers 
        // the appropriate delegate creation syntax:
        //    new ParameterizedThreadStart(w.DoMoreWork)
        //
        Work w = new Work();
        newThread = new Thread(w.DoMoreWork);

        // Pass an object containing data for the thread.
        //
        newThread.Start("The answer.");
    }

    public static void DoWork(object data)
    {
        Console.WriteLine("Static thread procedure. Data='{0}'",
            data);
    }

    public void DoMoreWork(object data)
    {
        Console.WriteLine("Instance thread procedure. Data='{0}'",
            data);
    }
}

/* This code example produces the following output (the order 
   of the lines might vary):

Static thread procedure. Data='42'
Instance thread procedure. Data='The answer'
*/