Java中的并行数组拷贝

Question

I'm looking to copy an array into another in parallel , for example:

int[] a = {1, 3, 5, 7, 9};
int[] b = new int[a.length];
for(int i = 0; i < a.length; i++) // parallel
{
   b[i] = a[i];
}

In this example I would like one thread to copy the first 3 indexes, and another to copy the other 2. Of course it can be in any other variation as well.

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Things to consider:

1. I am planning to run this on very large arrays so a small overhead is ok
2. There might be more code added to the loop body, for example another array - c which will get a[i]+1

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What I have tried:

1. IntStream.range :

    IntStream.range(0, a.length).parallel().forEach(i -> {
        b[i] = a[i];
    });

This resulted in Local variable percentiles defined in an enclosing scope must be final or effectively final error since b is not final and cannot be assigned.

2. fork/join: might be it, but looking for other solution which does not involve declaring a new class or extending the existing one.

Answer 1

There's no reason to do this in parallel; because you're working with an int[] , you can use clone() to copy it:

int[] a = {1, 3, 5, 7, 9};
int[] b = a.clone();

If, for some reason, you still want to do this in parallel, then you can use Arrays#parallelSetAll :

Arrays.parallelSetAll(b, i -> a[i]);

For each snippet, the elements of b are equivalent:

[1, 3, 5, 7, 9]