MultiThread

How Cherno explain about Thread

How we could do multi-thread(parallel computating)

#include <iostream>
#include <thread>

static bool s_Finished = false;

void DoWork(){
    while(!s_Finished){
        std::cout<<"Working...."<<std::endl();
    }
}

int main(){
    std::thread worker(DoWork); //pass as Function pointer

    std::cin.get();
    s_Finished = true;

    worker.join();

    std::cin.get(); // this line will wait until the threads(worker) joined.
}

Here we want program to do two things at the same time.

1. keep printing Working....
2. receive the cin.get() from user, once get something from the user s_Finished = true

thread::join

The behavior will be like this

However we might not want to let one single thread occupy whole CPU resource, we can use std::this_thread::sleep_for(1s).

#include <iostream>
#include <thread>

static bool s_Finished = false;
void DoWork() {
	using namespace std::literals::chrono_literals;
	std::cout << "Started thread id=" << std::this_thread::get_id() << std::endl;
	while (!s_Finished) {
		std::cout << "Working...\n";
		std::this_thread::sleep_for(1s); //sleep for a second
	}
}

int main(){
	std::thread worker(DoWork);
	std::cin.get();
	s_Finished = true;
	worker.join(); //await in C#

	std::cout << "Finished\n";
	std::cout << "Started thread id=" << std::this_thread::get_id() << std::endl;

	std::cin.get();
}

The demo of code above.

Can notice that two std::this_thread::get_id() are different, cuz they are on the different threads.

How we could implement multi-thread in Grasshopper

Grasshopper Tutorial

Like this tutorial shown, we can use

System.Threading.Tasks.Parallel.For(0, loopCount, i =>{ {
    //for loop body
}});

instead of using regular for-loop to achieve multi-thread.

unsafe problem and how to tackle it

This is the part I might not fully understand, and you are welcome to correct me. Thanks.
Seems simply use multi_thread with List, like the example in tutorial, is not safe.
Means multi-thread cannot merge to the List in the order correctly. As a result, this cause some data lost.

How we can tackle this problem

1. We can use lock syntax to ensure the action of List
2. We use regular array instead of List

Here are the codes.

Lock

private void RunScript(List<Point3d> startPts, object y, ref object A)
  {
    List<Point3d> ptList = new List<Point3d>();
    //for(int i = 0;i < startPts.Count; i++)
    System.Threading.Tasks.Parallel.For(0, startPts.Count, i => {
      {
        //Declare out agent location
        Point3d agentLoc = startPts[i];
        //Add agents to ptLists
        lock(ptList){
          ptList.Add(agentLoc);
        }
      }
      });
    A = ptList;
  }

array

private void RunScript(List<Point3d> startPts, object y, ref object A)
  {
    //List<Point3d> ptList = new List<Point3d>();
    Point3d[] ptList = new Point3d[startPts.Count];
    //for(int i = 0;i < startPts.Count; i++)
    System.Threading.Tasks.Parallel.For(0, startPts.Count, i => {
      {
        //Declare out agent location
        Point3d agentLoc = startPts[i];
        //Add agents to ptLists
        ptList[i] = agentLoc;
      }
      });
    A = ptList;
  }

Rhino Official Documents_General Overview

multi-thread

Rhino Official Documents_Developer

Task Capable Component

Overview

Grasshopper for Rhino6 allows you to develop mult-threaded components by way of the new IGH_TaskCapableComponent interface. Benchmarks have shown that Grasshopper can run significantly faster when using multi-threaded components. Results may vary, as not all solutions can be compute in parallel

The Interface

When a component implement the IGH_TaskCapableComponent interface, Grasshopper will notice and potentially call a full enumeration of SolveInstance for the component twice in consecutive passes:

1. The first pass is for collecting data and starting tasks to compute result
2. The second pass is for using the results from the tasks to sets outputs.

https://discourse.mcneel.com/t/v6-feature-multi-threaded-gh-components/47049

I found that there are some Rhino official posts talk about mult-threaded in grasshopper.
From User interface, if you see the component has two grey dots on its upper-left corner, means that component support mult-threaded computation(parallel computing).

Still working on…. To be continue

(James_Ramsden_Multithreading)[http://james-ramsden.com/multithreading-a-foreach-loop-in-a-grasshopper-components-in-c/]