}

    public void execute() {
      RunnableExecutorPair stack;
      do {
        stack = head;
        if (stack == null) {
          // If head == null then execute() has been called so we should just return
          return;
        }
        // try to swap null into head.
      } while (!UNSAFE.compareAndSwapObject(this, HEAD_OFFSET, stack, null));

    Node<K, V> head;
    Node<K, V> tail;
    int count;

    KeyList(Node<K, V> firstNode) {
      this.head = firstNode;
      this.tail = firstNode;
      firstNode.previousSibling = null;
      firstNode.nextSibling = null;
      this.count = 1;
    }
  }

  @CheckForNull private transient Node<K, V> head; // the head for all keys

    List<E> head = list.subList(0, size - 1);
    List<E> tail = list.subList(1, size);
    assertEquals(list.get(0), copy.get(0));
    assertEquals(list.get(size - 1), copy.get(size - 1));
    assertEquals(list.get(1), tail.get(0));
    assertEquals(list.get(size - 1), tail.get(size - 2));
    assertEquals(list.get(0), head.get(0));
    assertEquals(list.get(size - 2), head.get(size - 2));

    List<E> head = list.subList(0, size - 1);
    List<E> tail = list.subList(1, size);
    assertEquals(list.get(0), copy.get(0));
    assertEquals(list.get(size - 1), copy.get(size - 1));
    assertEquals(list.get(1), tail.get(0));
    assertEquals(list.get(size - 1), tail.get(size - 2));
    assertEquals(list.get(0), head.get(0));
    assertEquals(list.get(size - 2), head.get(size - 2));

    testSubMultisetEntrySet(SubMultisetSpec.HEAD_CLOSED);
  }

  public void testHeadClosedSize() {
    testSubMultisetSize(SubMultisetSpec.HEAD_CLOSED);
  }

  public void testHeadClosedDistinctElements() {
    testSubMultisetDistinctElements(SubMultisetSpec.HEAD_CLOSED);
  }

  public void testHeadOpenEntrySet() {
    testSubMultisetEntrySet(SubMultisetSpec.HEAD_OPEN);
  }

                .named("ImmutableDoubleArray.asList"),
            ListTestSuiteBuilder.using(new ImmutableDoubleArrayHeadSubListAsListGenerator())
                .named("ImmutableDoubleArray.asList, head subList"),
            ListTestSuiteBuilder.using(new ImmutableDoubleArrayTailSubListAsListGenerator())
                .named("ImmutableDoubleArray.asList, tail subList"),

                .named("ImmutableLongArray.asList"),
            ListTestSuiteBuilder.using(new ImmutableLongArrayHeadSubListAsListGenerator())
                .named("ImmutableLongArray.asList, head subList"),
            ListTestSuiteBuilder.using(new ImmutableLongArrayTailSubListAsListGenerator())
                .named("ImmutableLongArray.asList, tail subList"),

        segment.newEntryForTesting(keyThree, hashThree, entryTwo);
    segment.setValueForTesting(entryThree, valueThree);

    // alone
    assertNull(segment.removeFromChainForTesting(entryOne, entryOne));

    // head
    assertSame(entryOne, segment.removeFromChainForTesting(entryTwo, entryTwo));

    // middle
    InternalEntry<Object, Object, ?> newFirst =
        segment.removeFromChainForTesting(entryThree, entryTwo);

        segment.newEntryForTesting(keyThree, hashThree, entryTwo);
    segment.setValueForTesting(entryThree, valueThree);

    // alone
    assertNull(segment.removeFromChainForTesting(entryOne, entryOne));

    // head
    assertSame(entryOne, segment.removeFromChainForTesting(entryTwo, entryTwo));

    // middle
    InternalEntry<Object, Object, ?> newFirst =
        segment.removeFromChainForTesting(entryThree, entryTwo);

    }

    public void execute() {
      RunnableExecutorPair stack;
      do {
        stack = head;
        if (stack == null) {
          // If head == null then execute() has been called so we should just return
          return;
        }
        // try to swap null into head.
      } while (!UNSAFE.compareAndSwapObject(this, HEAD_OFFSET, stack, null));