Simplest way to run three methods in parallel in C#

Question

I have three methods that I call to do some number crunching that are as follows

results.LeftFront.CalcAi();  
results.RightFront.CalcAi();  
results.RearSuspension.CalcAi(geom, vehDef.Geometry.LTa.TaStiffness, vehDef.Geometry.RTa.TaStiffness);

Each of the functions is independent of each other and can be computed in parallel with no dead locks.
What is the easiest way to compute these in parallel without the containing method finishing until all three are done?

Solution 1

See the TPL documentation. They list this sample:

Parallel.Invoke(() => DoSomeWork(), () => DoSomeOtherWork());

So in your case this should just work:

Parallel.Invoke(
    () => results.LeftFront.CalcAi(),
    () => results.RightFront.CalcAi(),
    () => results.RearSuspension.CalcAi(geom, 
                                        vehDef.Geometry.LTa.TaStiffness, 
                                        vehDef.Geometry.RTa.TaStiffness));

EDIT: The call returns after all actions have finished executing. Invoke() is does not guarantee that they will indeed run in parallel, nor does it guarantee the order in which the actions execute.

Solution 2

You can do this with tasks too (nicer if you later need Cancellation or something like results)

var task1 = Task.Factory.StartNew(() => results.LeftFront.CalcAi());
var task2 = Task.Factory.StartNew(() => results.RightFront.CalcAi());
var task3 = Task.Factory.StartNew(() =>results.RearSuspension.CalcAi(geom, 
                              vehDef.Geometry.LTa.TaStiffness, 
                              vehDef.Geometry.RTa.TaStiffness));

Task.WaitAll(task1, task2, task3);

Solution 3

In .NET 4, Microsoft introduced the Task Parallel Library which was designed to handle this kind of problem, see Parallel Programming in the .NET Framework.

Solution 4

To run parallel methods which are independent of each other ThreadPool.QueueUserWorkItem can also be used. Here is the sample method-

public static void ExecuteParallel(params Action[] tasks)
{
    // Initialize the reset events to keep track of completed threads
    ManualResetEvent[] resetEvents = new ManualResetEvent[tasks.Length];

    // Launch each method in it's own thread
    for (int i = 0; i < tasks.Length; i++)
    {
        resetEvents[i] = new ManualResetEvent(false);
        ThreadPool.QueueUserWorkItem(new WaitCallback((object index) =>
            {
                int taskIndex = (int)index;

                // Execute the method
                tasks[taskIndex]();

                // Tell the calling thread that we're done
                resetEvents[taskIndex].Set();
            }), i);
    }

    // Wait for all threads to execute
    WaitHandle.WaitAll(resetEvents);
}

More detail about this function can be found here:
http://newapputil.blogspot.in/2016/03/running-parallel-tasks-using.html

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Comments

[sll]

You only interested in task parallel lib solution? What about straightforward Delegate.BeginInvoke() or even Thread.Start()?

[Random Dev]

he want to wait for all results - you can do this with what you suggest but have to do the sync by yourself - IMHO you should use Task as long there isn't some really good reason not to do - this will get even more important if C#/async goes live

[PlTaylor]

All the thread start examples I have found don't wait until the group of functions complete.

[Random Dev]

No they don't and you should really use the Task-Library for this kind of stuff. IMHO MS is pushing this approach with async and it is really a nice lib (almost as good as F#'s async-workflows :D )

[Jonathan]

Will this wait until all Parallel tasks are completed?

[PlTaylor]

For all the searching I have done, it seems as though most people have left out this simple example. Thanks for the quick response and great answer.

[Libor]

@Jonathan It will wait. The construct is similar to starting several tasks and then calling Task.WaitAll.

[Microsoft Developer]

Possibly not a good idea to use start new see: (blog.stephencleary.com/2013/08/startnew-is-dangerous.html)

[Random Dev]

@dotNETNinja true now - this answer is quite old (as you can see) - there was no async then - anyhow you can just switch it with Task.Run as adviced by the link you provided - given you may use .net4.5 (or newer)

[Ziggler]

I have something similar here.. stackoverflow.com/questions/30261335/…

[Eli Arbel]

Parallel also uses the current thread to execute actions, so it's not blocking a thread waiting for the actions to be completed. If you have synchronous, CPU-bound operations you need to parallelize, it's a better choice.

[F11]

how to get return values from different methods