@Override
        public void execute(Vertex vertex, Messenger<Long> messenger, Memory memory) {
            switch (memory.getIteration()) {
                case 0:
                    if (vertex.value("name").equals("josh")) {
                        messenger.sendMessage(this.countMessageScopeIn, 2L);
                        messenger.sendMessage(this.countMessageScopeOut, 1L);
                    }
                    break;
                case 1:
                    long edgeCount = IteratorUtils.reduce(messenger.receiveMessages(), 0L, (a, b) -> a + b);
                    vertex.property(MEMORY_KEY, edgeCount);
                    break;
            }
        }
Javadoc for {@code ConcurrentSkipListSet} includes this little note: "Beware that, unlike in most
collections, the size method is not a constant-time operation." Doing a traversal of elements will yield
the correct count. Java 11 upgrade seemed to force this failure consistently.
gremlin-test/src/main/java/org/apache/tinkerpop/gremlin/process/computer/GraphComputerTest.java