Question

Here is the context: I am writing an interpreter in C# for a small programming language called Heron, and it has some primitive list operations which can be executed in parallel.

One of the biggest challenges I am facing is to distribute the work done by the evaluator across the different cores effectively whenever a parallelizable operation is encountered. This can be a short or long operation, it is hard to determine in advance.

One thing that I don’t have to worry about is synchronizing data: the parallel operations are explicitly not allowed to modify data.

So the primary questions I have is:

• What is the most effective way to distribute the work across threads, so that I can guarantee that the computer will distribute the work across two cores?

I am also interested in a related question:

• Roughly how long should an operation take before we can start overcoming the overhead of separating the work onto another thread?

Answer 1

If you want to do a lot with parallel operations, you’re going to want to start with .Net 4.0. Here’s the Parallel Programming for .Net documentation. You’ll want to start here though. .Net 4.0 adds a LOT in terms of multi-core utilization. Here’s a quick example:

Current 3.5 Serial method:

for(int i = 0; i < 30000; i++)
{
  doSomething(i);
}

New .Net 4.0 Parallel method:

Parallel.For(0, 30000, (i) => doSomething(i));

The Parallel.For method automatically scales across the number of cores available, you can see how fast you could start taking advantage of this. There are dozens of new libraries in the framework, supporting full thread/task management like your example as well (Including all the piping for syncing, cancellation, etc).

There are libraries for Parallel LINQ (PLINQ), Task Factories, Task Schedulers and a few others. In short, for the specific task you laid out .Net 4.0 has huge benefits for you, and I’d go ahead and grab the free beta 2 (RC coming soon) and get started. (No, I don’t work for Microsoft…but rarely do I see an upcoming release fulfill a need so perfectly, so I highly recommend .Net 4.0 for you)