Steven,
Looks like there is even more that could potentially be leaked -- since key
and value serializers are created and configured at the end, even the IO
thread allocated by the producer could leak. Given that, I think 1 isn't a
great option since, as you said, it doesn't really address the underlying
issue.
3 strikes me as bad from a user experience perspective. It's true we might
want to introduce additional constructors to make testing easier, but the
more components I need to allocate myself and inject into the producer's
constructor, the worse the default experience is. And since you would have
to inject the dependencies to get correct, non-leaking behavior, it will
always be more code than previously (and a backwards incompatible change).
Additionally, the code creating a the producer would have be more
complicated since it would have to deal with the cleanup carefully whereas
it previously just had to deal with the exception. Besides, for testing
specifically, you can avoid exposing more constructors just for testing by
using something like PowerMock that let you mock private methods. That
requires a bit of code reorganization, but doesn't affect the public
interface at all.
So my take is that a variant of 2 is probably best. I'd probably do two
things. First, make close() safe to call even if some fields haven't been
initialized, which presumably just means checking for null fields. (You
might also want to figure out if all the methods close() calls are
idempotent and decide whether some fields should be marked non-final and
cleared to null when close() is called). Second, add the try/catch as you
suggested, but just use close().
-Ewen
On Mon, Apr 13, 2015 at 3:53 PM, Steven Wu <stevenz...@gmail.com> wrote:
> Here is the resource leak problem that we have encountered when 0.8.2 java
> KafkaProducer failed in constructor. here is the code snippet of
> KafkaProducer to illustrate the problem.
>
> -------------------------------
> public KafkaProducer(ProducerConfig config, Serializer<K> keySerializer,
> Serializer<V> valueSerializer) {
>
> // create metrcis reporter via reflection
> List<MetricsReporter> reporters =
>
> config.getConfiguredInstances(ProducerConfig.METRIC_REPORTER_CLASSES_CONFIG,
> MetricsReporter.class);
>
> // validate bootstrap servers
> List<InetSocketAddress> addresses =
>
> ClientUtils.parseAndValidateAddresses(config.getList(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG));
>
> }
> -------------------------------
>
> let's say MyMetricsReporter creates a thread in constructor. if hostname
> validation threw an exception, constructor won't call the close method of
> MyMetricsReporter to clean up the resource. as a result, we created thread
> leak issue. this becomes worse when we try to auto recovery (i.e. keep
> creating KafkaProducer again -> failing again -> more thread leaks).
>
> there are multiple options of fixing this.
>
> 1) just move the hostname validation to the beginning. but this is only fix
> one symtom. it didn't fix the fundamental problem. what if some other lines
> throw an exception.
>
> 2) use try-catch. in the catch section, try to call close methods for any
> non-null objects constructed so far.
>
> 3) explicitly declare the dependency in the constructor. this way, when
> KafkaProducer threw an exception, I can call close method of metrics
> reporters for releasing resources.
> KafkaProducer(..., List<MetricsReporter> reporters)
> we don't have to dependency injection framework. but generally hiding
> dependency is a bad coding practice. it is also hard to plug in mocks for
> dependencies. this is probably the most intrusive change.
>
> I am willing to submit a patch. but like to hear your opinions on how we
> should fix the issue.
>
> Thanks,
> Steven
>
--
Thanks,
Ewen
