spark core 2.0 MemoryBlock Soruce Code Analysis

MemoryBlock contains a consecutive block of memory, starting at a
MemoryLocation with a  fixed size.

public class MemoryBlock extends MemoryLocation {

private final long length;

/**
* Optional page number; used when this MemoryBlock represents a page allocated by a
* TaskMemoryManager. This field is public so that it can be modified by the TaskMemoryManager,
* which lives in a different package.
*/
public int pageNumber = -1;

public MemoryBlock(@Nullable Object obj, long offset, long length) {
super(obj, offset);
this.length = length;
}

/**
* Returns the size in bytes of the memory block.
*/
public long size() {
return length;
}

/**
* Creates a memory block pointing to the memory used by the long array.
*/
public static MemoryBlock fromLongArray(final long[] array) {
return new MemoryBlock(array, Platform.LONG_ARRAY_OFFSET, array.length * 8L);
}
}