java byte：I can't understand the usage here

Question

byte: Why, what's the use of doing this

{ byte p000, p001, p002, p003, p004, p005, p006, p007; ... }

/** The namespace for field padding through inheritance. */
final class BLCHeader {
  abstract static class PadDrainStatus<K, V> extends AbstractMap<K, V> {
    byte p000, p001, p002, p003, p004, p005, p006, p007;
    byte p008, p009, p010, p011, p012, p013, p014, p015;
    byte p016, p017, p018, p019, p020, p021, p022, p023;
    
    ...
    byte p088, p089, p090, p091, p092, p093, p094, p095;
    byte p096, p097, p098, p099, p100, p101, p102, p103;
    byte p104, p105, p106, p107, p108, p109, p110, p111;
    byte p112, p113, p114, p115, p116, p117, p118, p119;
  }

  /** Enforces a memory layout to avoid false sharing by padding the drain status. */
  abstract static class DrainStatusRef<K, V> extends PadDrainStatus<K, V> {
    static final VarHandle DRAIN_STATUS;

    ...
}

it comes from caffeine source code:https://github.com/ben-manes/caffeine/blob/master/caffeine/src/main/java/com/github/benmanes/caffeine/cache/BoundedLocalCache.java

Answer 1

Given that this is a concurrent cache, the padding is there to prevent cache line sharing. A cache line is the unit of memory that's loaded into the cache by the CPU. The actual size will vary by CPU design, but a minimum size of 64 bytes is typical. Just search the net using some of these terms and you'll find more information.