CI never ends for unit tests with manual test container lifecycle control

[guillermocalvo]

Steps to reproduce the problem:

• A unit test must create a singleton kafka container.
• There must be some kafka consumer in the application context.

Example:

@MicronautTest
@TestInstance(TestInstance.Lifecycle.PER_CLASS)
class MyTest implements TestPropertyProvider {

  static final KafkaContainer MY_KAFKA = new KafkaContainer(DockerImageName.parse("confluentinc/cp-kafka:latest"));
  static { MY_KAFKA.start(); }

  @Override
  public Map<String, String> getProperties() {
    return Map.of("kafka.bootstrap.servers", MY_KAFKA.getBootstrapServers());
  }

  @Test
  void testKafkaRunning(MyProducer producer) {
    producer.produce("hello");
  }

  @KafkaClient interface MyProducer {
    @Topic("my-topic")
    void produce(String message);
  }

  @KafkaListener static class MyConsumer {
    @Topic("my-topic")
    public void consume(String message) { }
  }
}

At the end of the test, the "main" thread will try to detect if the kafka consumer is closed:

    @Override
    @PreDestroy
    public void close() {
        for (ConsumerState consumerState : consumers.values()) {
            consumerState.kafkaConsumer.wakeup();
        }
        for (ConsumerState consumerState : consumers.values()) {
            while (consumerState.closedState == ConsumerCloseState.POLLING) {
                LOG.trace("consumer not closed yet");
            }
        }
        consumers.clear();
    }

Since consumerState.closedState was updated by another thread, the "main" thread will use a cached version of this value indefinitely (ie. "consumer not closed yet").

By declaring this field as volatile we will prevent the "main" thread from caching its value.

The lifecycle of this field is NOT_STARTED -> POLLING -> CLOSED. It's set when the state changes and it's only queried when the kafka consumer is destroyed, so the performance penalty should be negligible.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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[sdelamo]

@yawkat can you review this PR?