ArrayPool

Sometimes in C# programs we want to allocate many arrays of similar lengths. These arrays may be needed only for short times.

To reuse an array from an ArrayPool, we "rent" it with the Rent() method. We can then Return() the same array to allow later uses.

Here we introduce a method called UseSharedArray that uses the ArrayPool generic type. We call UseSharedArray 3 times with a different number.

using System;
using System.Buffers;

class Program
{
    static void UseSharedArray(int x)
    {
        // Part 1: reference the ArrayPool and Rent an array.
        var shared = ArrayPool<int>.Shared;
        var rentedArray = shared.Rent(5);

        // Part 2: store values in rented array and print them.
        rentedArray[0] = 0;
        rentedArray[1] = 1 * x;
        rentedArray[2] = 2 * x;
        rentedArray[3] = 3 * x;
        rentedArray[4] = 4 * x;
        // ... Print integers.
        for (int i = 0; i < 5; i++)
        {
            Console.WriteLine("ARRAY {0}: {1}", x, rentedArray[i]);
        }

        // Part 3: return the rented array.
        shared.Return(rentedArray);
    }

    static void Main()
    {
        UseSharedArray(1);
        UseSharedArray(2);
        UseSharedArray(3);
    }
}
ARRAY 1: 0
ARRAY 1: 1
ARRAY 1: 2
ARRAY 1: 3
ARRAY 1: 4
ARRAY 2: 0
ARRAY 2: 2
ARRAY 2: 4
ARRAY 2: 6
ARRAY 2: 8
ARRAY 3: 0
ARRAY 3: 3
ARRAY 3: 6
ARRAY 3: 9
ARRAY 3: 12

Static array

Sometimes we have simple array sharing requirements—only 1 array may be needed. We can just use a static array of a certain length.

using System;

class Program
{
    static int[] _shared = new int[5];

    static void UseStaticArray(int x)
    {
        var rentedArray = _shared;
        rentedArray[0] = 0;
        rentedArray[1] = 1 * x;
        rentedArray[2] = 2 * x;
        rentedArray[3] = 3 * x;
        rentedArray[4] = 4 * x;
        // ... Print integers.
        for (int i = 0; i < 5; i++)
        {
            Console.WriteLine("ARRAY {0}: {1}", x, rentedArray[i]);
        }
    }

    static void Main()
    {
        UseStaticArray(1);
        UseStaticArray(2);
        UseStaticArray(3);
    }
}
ARRAY 1: 0
ARRAY 1: 1
ARRAY 1: 2
ARRAY 1: 3
ARRAY 1: 4
ARRAY 2: 0
ARRAY 2: 2
ARRAY 2: 4
ARRAY 2: 6
ARRAY 2: 8
ARRAY 3: 0
ARRAY 3: 3
ARRAY 3: 6
ARRAY 3: 9
ARRAY 3: 12

For complex array sharing requirements, ArrayPool is a good choice. For simple programs where only one array is shared, a static array can be used.