[2.6.3-java] Thread leak

[Sascha Thiel]

Hey,

After a few reloads of a page my application crashes. I recognized that it creates tons of thread which seem not to be freed up again.

In Visual VM I got the following graph. After each reloads the remaining thread count is a little higher and also after a while it does not get freed up again.

In the thread list, it looks like this.

I, unfortunately, do not have a single clue where I should start to search for the issue. I hope you can point me into the right direction.

Thanks in advance.

Sascha

[Sascha Thiel]

I additionally found out, that after each reload, two more AsyncHttpClient and two more of those pool-xxx-thred-xx gets created, see picture below.

[Sascha Thiel]

OK, I found the issue. Thanks for listening. :-D

[Koen De Groote]

I'm interested in what the cause of this could be, if you wouldn't mind sharing.

I'm not a Play developer, so I would probably not have been of help looking into it, but still, it's interesting.

[Sascha Thiel]

Hey, 

It was a super stupid mistake on my side.

I created a proxy to serve avatars from gravatar like this.

try (final AsyncHttpClient asyncHttpClient = new DefaultAsyncHttpClient()) {

final BoundRequestBuilder requestBuilder = asyncHttpClient.prepareGet(avatarUrl);

final Future<Response> featureResponse = requestBuilder.execute();

final Response response = featureResponse.get();

final InputStream responseBodyAsStream = response.getResponseBodyAsStream();

return ok(responseBodyAsStream).as("image/jpg");

} catch (Exception e) {

return notFound();

}

And in the previous version I forgot to close the AsyncHttpClient. So whenever an avatar was loaded, two threads kept running. The explanation to you helped me finding the bug. :-D

Bests,

Sascha

[Koen De Groote]

Thanks for elaborating.

It's strange though, I would expect the ok() method to close off all threads that got started when the route was called.

[Will Sargent]

You're supposed to inject a WSClient, and let Play handle the thread management under normal circumstances.

https://www.playframework.com/documentation/2.6.x/JavaWS#Directly-creating-WSClient

"Note: If you create a WSClient manually then you must call client.close() to clean it up when you’ve finished with it. Each client creates its own thread pool. If you fail to close the client or if you create too many clients then you will run out of threads or file handles -— you’ll get errors like “Unable to create new native thread” or “too many open files” as the underlying resources are consumed."