Parallel. To skip items

Question

In the following code, it seems that only every other element of the array is populated. Why?

Random rand = new Random();
int byteLength = 10000000;
var result = new byte[10][];
Parallel.For(0, 10, (i) =>
{
    int length = rand.Next(byteLength);
    var tempResult = new byte[length];
    Thread.Sleep(100);
    rand.NextBytes(tempResult);
    result[i] = tempResult;
});

Contrast with this (non-parallel) code that fills each element:

rand = new Random();
var result2 = new byte[10][];
for (int i = 0; i < 10; i++)
{
    int length = rand.Next(byteLength);
    var tempResult = new byte[length];
    Thread.Sleep(100);
    rand.NextBytes(tempResult);
    result2[i] = tempResult;
}

Comparing with the examples in the documents on MSDN, I suspect that this is because it resultis located outside the delegate Parallel.For- thus, streams occur when accessing result. But, as a newbie to multithreading, I'm not sure if that is the case.

Answer 1

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