RFR: 8294916: Cancelling a request must eventually cause its response body subscriber to be unregistered [v6]

[Michael McMahon]

On Tue, 18 Oct 2022 13:37:42 GMT, Daniel Fuchs <dfuchs at openjdk.org> wrote:

>> test/jdk/java/net/httpclient/SmallTimeout.java line 86:
>> 
>>> 84:         HttpClient client = HttpClient.newHttpClient();
>>> 85:         ReferenceTracker.INSTANCE.track(client);
>>> 86:         Reference<HttpClient> reference = new WeakReference<>(client);
>> 
>> I don't understand the use of `WeakReference` here. I see that we have a `ReachabilityFence` for the `client` in the `finally` block of this test where we then null out `client`. So, if I'm understanding this right, this `WeakReference` is essentially a no-op. i.e. we probably don't need it because we are anyway holding on to the `client` for the lifetime of this test program?
>
> The reference is passed to another thread but should remain alive until that other thread has terminated - which is ensured by waiting for the executor to shutdown. What happens here is that the test failed because the other threads started in this block were keeping the reference alive. I'm using a reference here because passing `client` to a lambda makes `client` final and that prevents me from nulling out the `client` variable before calling `gc`. Using a weak reference solves the issue (since I don't have to null it and it won't keep the client alive).

I'm still unclear as to why the other threads were keeping the reference alive though?

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PR: https://git.openjdk.org/jdk/pull/10659