OpcUaMonitoredItem does not cache the last DataValue

tosuns commented 8 years ago

It seems like the above mentioned instance does not cache the last retrieved value. Therefore if a value consumer is added after the value was published the consumer will not get the value until a data value change notification occurrs again. In case of data points whose values do not change very frequently, the user is forced to actually invoke a read operation.

I noticed this behaviour while modifying the "testSubscribe" test case. Instead of subscribing only one monitored item I tried to subscribe two items at once. The test always failed because of a time out exception. The value of the first item will be printed out like expected, but the second causes the time out exception, because the consumer was registered and its get-method gets called after the notification occurred, which is to late.

` public void testSubscribe() throws Exception { LOG.info("testSubscribe()");

    // create a subscription and a monitored item
    UaSubscription subscription = opcUaClient.getSubscriptionManager()
            .createSubscription(1000.0)
            .get();

    AtomicInteger clienthandles = new AtomicInteger(1);

    List<MonitoredItemCreateRequest> requests = Arrays.asList(
            new NodeId(4,
                       "<datapoint.one>"),
            new NodeId(4,
                       "<datapoint.two>"))
            .stream()
            .map(nodeId -> new ReadValueId(
                    nodeId,
                    AttributeId.Value.uid(),
                    null,
                    QualifiedName.NULL_VALUE))
            .map((readValueId) -> {
                final int clientHandle = clienthandles.getAndIncrement();
                MonitoringParameters parameters = new MonitoringParameters(
                        uint(clientHandle),
                        1000.0,
                        null,
                        uint(10),
                        true);
                MonitoredItemCreateRequest request = new MonitoredItemCreateRequest(
                        readValueId,
                        MonitoringMode.Reporting,
                        parameters
                );
                return request;
            })
            .collect(Collectors.toList());

    List<UaMonitoredItem> items = subscription
            .createMonitoredItems(TimestampsToReturn.Both,
                                  Collections.unmodifiableList(requests)).get();

    // do something with the value updates
    items.forEach((item) -> {

        try {
            LOG.log(Level.INFO,
                    "item [clientHandle: {0}, monitoreditemId: {1}",
                    new Object[]{item.getClientHandle(),
                                 item.getMonitoredItemId()});
            CompletableFuture<DataValue> f = new CompletableFuture<>();

            item.setValueConsumer(f::complete);
            DataValue datavalue = f.get(15, TimeUnit.SECONDS);

            assertNotNull(datavalue);
            assertNotNull(datavalue.getValue());
            LOG.log(Level.INFO, "subscribtion Result: {0}",
                    datavalue.getValue().getValue());
        } catch (InterruptedException |
                 TimeoutException |
                 ExecutionException ex) {
            LOG.log(Level.SEVERE, null, ex);
            fail(ex.getMessage());
        }

    });

}`