spark core 2.0 LongArray

LongArray is an array of long values. Compared with native JVM arrays, this:

1. supports using both in-heap and off-heap memory.

2. has no bound checking, and thus can crash the JVM process when assert is turned off.

The main fields and constructor of LongArray
// This is a long so that we perform long multiplications when computing offsets.
private static final long WIDTH = 8;

private final MemoryBlock memory;
private final Object baseObj;
private final long baseOffset;

private final long length;

public LongArray(MemoryBlock memory) {
assert memory.size() < (long) Integer.MAX_VALUE * 8: "Array size > 4 billion elements";
this.memory = memory;
this.baseObj = memory.getBaseObject();
this.baseOffset = memory.getBaseOffset();
this.length = memory.size() / WIDTH;
}
The set and get method, note that the position the combination of  baseOffset and index * WIDTH.
/**
* Sets the value at position {@code index}.
*/
public void set(int index, long value) {
assert index >= 0 : "index (" + index + ") should >= 0";
assert index < length : "index (" + index + ") should < length (" + length + ")";
Platform.putLong(baseObj, baseOffset + index * WIDTH, value);
}

/**
* Returns the value at position {@code index}.
*/
public long get(int index) {
assert index >= 0 : "index (" + index + ") should >= 0";
assert index < length : "index (" + index + ") should < length (" + length + ")";
return Platform.getLong(baseObj, baseOffset + index * WIDTH);
}