Parallel.Foreach and yield return

Question

I want to do something like this:

foreach (var e in source)
   yield return e;

with a Parallel.Foreach?

Is it possible and if yes, how

Answer 1

You'll need to make the enumerator separate from your loop, but process it in parallel.  Yield return will return a value of the enumerable collection - this wouldn't make sense, because one object would be using the enumeration NOT in parallel, but trying to return parallelized...

The normal way you'd do this is like:

// In your source, you use yield
public ClassImplementingIEnumerable: IEnumerable<int>
{
     public IEnumerable<int> GetSource()
     {
           for (int i=0;i<1000;++i)
               yield return i;
     }
}


public class ParallelProcessingConsumer {

    public void SomeMethod(ClassImplementingIEnumerable sourceProvider)
    {
      
          Parallel.ForEach(sourceProvider.GetSource(), parallelOptions, (i, loopState) =>
          { 
             // Do work in parallel!
          });
    }

---

Reed Copsey, Jr. - http://reedcopsey.com

Answer 2

Matthieu, are you looking to consume an iterator with a Parallel.ForEach, or implement an iterator with a Parallel.ForEach?  Reed's answer addresses the former.