157. Tackling the slicing allocator

Let’s consider the following three Java regular int arrays:

int[] arr1 = new int[]{1, 2, 3, 4, 5, 6};
int[] arr2 = new int[]{7, 8, 9};
int[] arr3 = new int[]{10, 11, 12, 13, 14};

Next, we want to allocate a memory segment to each of these arrays. A straightforward approach relies on Arena.allocateArray() introduced in Problem 150:

try (Arena arena = Arena.ofConfined()) {
  MemorySegment segment1 
    = arena.allocateArray(ValueLayout.JAVA_INT, arr1);
  MemorySegment segment2 
    = arena.allocateArray(ValueLayout.JAVA_INT, arr2);
  MemorySegment segment3 
    = arena.allocateArray(ValueLayout.JAVA_INT, arr3);
}

This approach allocates enough memory to accommodate each of the given arrays. But, sometimes, we want to allocate only a certain amount of memory. If this fixed amount is not enough, then we want to tackle the problem differently. For this, we can rely on a java.lang.foreign.SegmentAllocator. Of course, there are...