How to configure a maximum number of threads in a Parallel.For

Question

This is the example microsoft presents for the parallel for, and I'd like to know how configure a maximum number of threads for this code.

     // A basic matrix multiplication.
     // Parallelize the outer loop to partition the source array by rows.
     System.Threading.Tasks.Parallel.For(0, matARows, i =>
     {
        for (int j = 0; j < matBCols; j++)
        {
           // Use a temporary to improve parallel performance.
           double temp = 0;
           for (int k = 0; k < matACols; k++)
           {
              temp += matA[i, k] * matB[k, j];
           }
           result[i, j] = temp;
        }
     }); // Parallel.For

Is that really the example presented? Because it's really invalid at the moment. Could you show where that's presented? — Jon Skeet
– Jon Skeet, Commented Apr 10, 2013 at 16:27
Yeah. Well, here I only presented the relevant fragment. The whole example is here: msdn.microsoft.com/en-us/library/dd460713.aspx — Alex. S.
– Alex. S., Commented Apr 10, 2013 at 16:34
You presented a fragment which is syntactically incorrect, by sticking "System.Threading.Tasks.TaskCreationOptions" in the middle of the argument list for no reason. — Jon Skeet
– Jon Skeet, Commented Apr 10, 2013 at 16:48
possible duplicate of Limit the number of parallel threads in C# — Sergey Malyutin
– Sergey Malyutin, Commented Oct 16, 2014 at 13:47

Jon Skeet · Accepted Answer · 2013-04-10 16:29:03Z

57

You need to specify a ParallelOptions value with a MaxDegreeOfParallelism:

For example:

Parallel.For(0, 10, new ParallelOptions { MaxDegreeOfParallelism = 4 }, count =>
{
    Console.WriteLine(count);
});

answered Apr 10, 2013 at 16:29

Jon Skeet

1.5m895 gold badges9.3k silver badges9.4k bronze badges

Sign up to request clarification or add additional context in comments.

Somnath Kadam Over a year ago

for Parallel for each use : Parallel.ForEach(lines,new ParallelOptions { MaxDegreeOfParallelism = 4 }, line => { Console.WriteLine(line); });

Sasha · Accepted Answer · 2013-04-10 16:39:05Z

6

Use MaxDegreeOfParalelism property for running the loop

Parallel.For(0, 1000, new ParallelOptions { MaxDegreeOfParallelism = 2 }, ...);

edited Apr 10, 2013 at 16:39

answered Apr 10, 2013 at 16:28

Sasha

8,9004 gold badges56 silver badges80 bronze badges

Comments

Tyler Lee · Accepted Answer · 2013-04-10 16:28:54Z

5

I'd suggest you take a look at the ParallelOption.MaxDegreesofParellelism and pass it into the For method

answered Apr 10, 2013 at 16:28

Tyler Lee

2,82517 silver badges24 bronze badges

Collectives™ on Stack Overflow

How to configure a maximum number of threads in a Parallel.For

3 Answers 3

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related