CDI Injection and waiting i.e. Thread.sleep()

Camunda 7 Topics Discussion & Questions
1

Hi everbody,

I wan´t to wait for a message to be available. I tried something like:

while (subscription == null && (System.currentTimeMillis() - startTime) < 30000) { try { Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } subscription = runtimeService .createEventSubscriptionQuery() .processInstanceId(instanceId) .eventType("message") .eventName(meassageTaskName.toString()) .singleResult(); }

It works but it looks very ugly. Is there some other trick, or a better pattern. The runtimeService is injected via CDI.

THX

2

You could attach an ExecutionListener to the corresponding Message Event in the process and notify your bean as the message becomes available. Be aware of the transacitonal semantics, though: the message will only be available in the database after the transaction is committed. If you are a CDI aficionado, then you could do it in an event driven way with a transactional observer which is invoked after commit.

However: your polling solution is not necessarily bad. It has the advantage that it is very robust: if you use a notification mechanism you need to account for the case when the handler cannot process the notificaiton successfully. The polling will inherently retry. However: it may be more efficient to not poll messages for each process instance individually but use a single poller thread (scheduled EJB) and then dispatch the results to some handlers.

3

Daniel, thx much for this very interesting ideas. I will investigate a few things. I think to do something with ExecutionListener is little more elegant.

grettings from Frankonia