Using TPL for parallel computing and RhinoCommon C# dot net

Rhino Developer
1

I have hundreds of brepbrep intersection, sweep function etc, which are making the tool quite slow.
So I want to use Task parallel library.
I had never used it before.
Would be nice to see a small source code, so would be easier for me to catch it.
It would help me to start with TPL with RhinoCommon c# dot net.

2

In certain cases parallel processing can be used, but Rhino is not thread-safe. I have encountered weird, unrepeatable crashes when doing stuff in parallel with TPL. Having said that, please see the example below.

Typically, if you have brep-brep intersection in a for loop like this:

Brep cutter;
Brep[] targets;
double tolerance = doc.ModelAbsoluteTolerance;

List<Curve> allCurves = new List<Curve>();
Point3dList allPoints = new Point3dList();
for (int i =0; i < targets.Length; ++i)
{
    Curve[] intersections;
    Point3d[] points;
    if (Intersection.BrepBrep(cutter, targets[i], tolerance, out intersections, out points))
    {
        if (null != intersections)
            allCurves.AddRange(intersections);
        if (null != points)
            allPoints.AddRange(points);
    }
}

you can make a TPL version like so

Brep cutter;
Brep[] targets;
double tolerance = doc.ModelAbsoluteTolerance;

ConcurrrentBag<Curve> allCurves = new ConcurrrentBag<Curve>();
ConcurrrentBag<Point3d> allPoints = new ConcurrrentBag<Point3d>();
Parallel.For (0, targets.Length, i => 
{
    Curve[] intersections;
    Point3d[] points;
    if (Intersection.BrepBrep(cutter, targets[i], tolerance, out intersections, out points))
    {
        if (null != intersections)
            foreach(var crv in intersections)
                allCurves.Add(crv);

        if (null != points)
            foreach(var pt in points)
                allPoints.Add(pt);
    }
});

The same goes for foreach loops, that get turned into Parallel.ForEach.

Because multiple threads access the allCurves and allPoints collections, you should use a thread-safe collection, like ConcurentBag<T>. It is good to realize that these collections are accessed by multiple threads, whereas the intersections and points arrays are local to each thread.

1 Like
3

Thank you so much ! It is a big help. I was not understanding how to use it at all. I had no clue.
I need to be prepared for un-expected crashes. At list I can see one example now and try it by trial and error now.

Many thanks !
:smile:

4

We have been experiencing crashes when trying to use Brep.CreatePlanarBreps in multiple threads simultaneously, so I would avoid that one.

5

Do you have a sample that causes a crash? We are always trying to make our geometry functions thread safe, but of course bugs do exist.

6

Here is the issue I submitted to Github in May: https://github.com/mcneel/rhinocommon/issues/167

7

Ah yes, the github bugtracker. We keep intending to move all of those issues from github to youtrack and close the one on github.

I’ve moved this report to youtrack at
http://mcneel.myjetbrains.com/youtrack/issue/RH-31012
Thanks!

8

I want to add curves as Rhino doc object from ConcurrrentBag allCurves.
How to write it ?

Can I draw all the curves at once in Rhino doc ?

9

No, you should just do this, outside of a parallel loop:

foreach(var crv in allCurves)
    doc.Objects.AddCurve(crv);
1 Like
10

@menno is correct. Any time you are adding items to or removing items from a list you should be doing this on a single thread. Only specialized collections like ConcurrentBag let you add items in a thread-safe way.

1 Like
11

Many thanks menno !

12

It is working ! Thanks.
speed looks almost same for drawing ConcurrrentBag Verses List