How to convert Parallel.For to PLINQ

问题

Parallel.For(0, Height, new ParallelOptions { MaxDegreeOfParallelism = 6 }, y =>
{
    int currentLine = y * BMPData.Stride;

    for (int x = 0; x < Width; x = x + BPX)
    {
        var b = pixels[currentLine + x];
        var g = pixels[currentLine + x + 1];
        var r = pixels[currentLine + x + 2];

        int avg = (r + g + b) / 3;
        pixels[currentLine + x] = (byte)avg;
        pixels[currentLine + x + 1] = (byte)avg;
        pixels[currentLine + x + 2] = (byte)avg;
    }
});

This is basically a parallel code where it turns bitmap data pixels into gray ones, but is there any way I can replace the Parallel.For usage with Parallel Linq? I know there's no point to this, but it's required for a certain assignment

回答1:

You can use Enumerable.Range, and ForAll to get similar results. Although note ForAll will not process the list in any stable order - which is probably fine for your use case

Enumerable.Range(0,Height)
          .AsParallel()
          .WithDegreeOfParallelism(6)
          .ForAll(y => 
{
   /// existing code here
});

回答2:

The ForAll Operator paragraph in the Introduction to PLINQ article has a ForAll example and ForAll seems to be perfect for what you do.
This example could be modified to your case

var nums = Enumerable.Range(0, Height);
var query =
    from num in nums.AsParallel().WithDegreeOfParallelism(6)
    select num;

// Process the results as each thread completes
query.ForAll(e => MakeGray(e));

where MakeGray is your pixel setting method.

This doesn't do any better than Jamiec's answer, but has some more fluff which may or may not be what you're looking for.

---

BTW. I think you could eliminate the 2nd for loop by using

Parallel.For(0, Width * Height / BPX, ...)

or

Enumerable.Range(0, Width * Height / BPX).AsParallel()...

and currentLine + x would just become x.

来源：https://stackoverflow.com/questions/65354440/how-to-convert-parallel-for-to-plinq