How to save different process result with Task.Factory.StartNew<>?

Question

My computer has 4 processor and I am trying to speed up my calculation times by using Task.Factory.StartNew<>. I want to save each process result in EachTastResult array. The problem is that below code does NOT save each process result separately! When I used 'Breakpoint' to see `EachTastResult Array' content, I realized that Final process result saved in EachTastResult[0],EachTastResult[1],EachTastResult[2] and EachTastResult[3]. While it should be as follow:

• EachTastResult[0]= 1th Process result
• EachTastResult[1]= 2th Process result
• EachTastResult[2]= 3th Process result
• EachTastResult[3]= 4th Process result

Excuse my bad English!

var tasks = new Task[4];
var EachTastResult = new int[4];

for (var proc = 0; proc < 4; proc++)
{
int procIndex = proc;    // Helper for closure

// Start one task per processor
tasks[proc] = Task.Factory.StartNew(() =>{

var NotExist_localCounter = 0;

for (var i = ((proc - 1) * foursec) + 1 ; i <= (proc * foursec); i++)
{
    if (condition_1 ...)
        if (Condition_2 ...)
            NotExist_localCounter++;
}
EachTastResult[procIndex] = NotExist_localCounter;
}, CancellationToken.None,TaskCreationOptions.None ,TaskScheduler.Default);}

Task.WaitAll(tasks);

NotExist_1 = EachTastResult.Sum();
label6.Text=NotExist_1.ToString();

where is my Mistake ?

Answer 1

I think the problem is that you're not using your "Helper for closure" consistently. Since each Task uses the shared proc variable, the you're computing the same result four times.