Use Parallel.ForEach without lists

Question

I want to use Parallel.ForEach as a multi-threading method that executes a code without lists or file reading.

I want to do it like this:

Parallel.ForEach
{
      Console.WriteLine("test");
}

So it will write test without stopping. I will use an IF statement to check if it should be stopped or no.

Is it possible to use Parallel.ForEach like that?

Any help would be appreciated.

Thanks!

Why would you wanna use a `foreach` loop without anything to iterate on? what's the main goal here? `ForEach` seems irrelevant. — Selman Genç, Aug 14 '18 at 21:51
@SelmanGenç - I want it to execute a normal code not iterated on a List. — Mario, Aug 14 '18 at 21:52
Why do you want to use a construct to iterate over a list you don't have? Please explain how would you do it using a normal `foreach` — Camilo Terevinto, Aug 14 '18 at 21:53
OP, it makes no sense to repeat something forever in parallel. That sentence isn't even comprehensible to me. What are you trying to do overall? — John Wu, Aug 14 '18 at 22:05
[`Parallel.Invoke`](https://learn.microsoft.com/en-us/dotnet/standard/parallel-programming/how-to-use-parallel-invoke-to-execute-parallel-operations)? — JSteward, Aug 14 '18 at 22:06
@JohnWu - I am trying to write `test` for example more faster by multi-threading. — Mario, Aug 14 '18 at 22:06
If you have a series of tests, wouldn't they be in a list, and wouldn't you iterate over that? If you don't have a series of tests but only a single test, again, I do not understand what your goal is here. — John Wu, Aug 14 '18 at 22:07
Instead of checking some condition in an `if` statements (as you mentioned in your question), you can just use it as a condition for a loop: `while (someCondition == true) { Console.WriteLine("Test"); }` — Rufus L, Aug 14 '18 at 22:32
`I want it to be multi-threaded.` **Why** do you want it multi-threaded? `Console.WriteLine` is going to use a locking mechanism anyway (i.e. will 'thwart' your attempts at multiple threads) - https://stackoverflow.com/questions/1079980/calling-console-writeline-from-multiple-threads . _If what you are trying to do is improve the performance of `Console.WriteLine` then reduce your number of calls to it. Don't write the string 100 times. Build a `string` which contains 100 lines of data and then call `Console.WriteLine` just once. It will be **way** quicker._ — mjwills, Aug 14 '18 at 23:44

Daniel Loudon · Answer 1 · 2018-08-14T22:14:37.463

Multi-threading this is not going to achieve anything, but if you insist:

bool _shouldStop { get; set; } = false;
bool _shouldStopSecondThread { get; set; } = false;

public static Main(string[] args)
{

Thread thread = new Thread(print);
Thread anotherThread = new Thread(anotherPrint);
thread.Start();
anotherThread.Start();

//your code here while the worker writes "Test" to console

if(condition) {
   _shouldStop=true;
   _shouldStopSecondThread=false; 
}
}    
//...

public void print()
{
   while (!_shouldStop)
   {
       Console.WriteLine("test");
   }
   Console.WriteLine("worker terminated");
}

public void anotherPrint()
{
   while (!_shouldStopSecondThread)
   {
       Console.WriteLine("test");
   }
   Console.WriteLine("worker terminated");
}

In addition I strongly suggest you to update to the Task API over the old Threading one. — Miguel, Aug 14 '18 at 22:13

Miguel · Accepted Answer · 2018-08-14T22:20:51.253

0

What you want is not very clear but you may try this approach:

        var parallelDrege = Environment.ProcessorCount;
        while (true)
        {
            Parallel.For(0, parallelDrege, t =>
            {
                Console.WriteLine("test");
            });
        }

Set parallelDegre to the desired value and be aware that every batch will be processed in parallel but from batch to batch is a sequetial process.

Hope this help!

edited Aug 14 '18 at 22:20

answered Aug 14 '18 at 22:10

Miguel

3,786
2
19
32

how do i terminate this ? – Daniel Loudon Aug 14 '18 at 22:15
go with the number of CPUs – Miguel Aug 14 '18 at 22:20
Environment.ProcessorCount – Miguel Aug 14 '18 at 22:20
or a factor of this: 2*Environment.ProcessorCount may be better – Miguel Aug 14 '18 at 22:21

Use Parallel.ForEach without lists

2 Answers2