Parent's MeterRegistry beans are closed when child context closes

[berry120]

MetricsAutoConfiguration contains a MeterRegistryCloser that ensures MeterRegistry instances are closed early in the shutdown process. However, this currently works by closing all such instances when any application context is closed. In the case where a child application context is created and then closed but the application is still running (i.e. the root context hasn't closed), the closure of this child context will then close all MeterRegistry instances prematurely.

(As a real-world example - when using the initializr library and calling ProjectGenerationInvoker.invokeProjectStructureGeneration, a ProjectGenerationContext is created, and then closed before the method returns - this then closes all the MeterRegistry instances defined in the application calling the initializr library.)

This fix ensures that the closure only happens when the root application context is being closed.

(I believe this is my first PR here, so happy to correct anything I may have done wrong!)

[wilkinsona]

Thanks for identifying the problem and proposing a fix. Unfortunately, I don't think this is quite right.

The currently proposed change will leave open indefinitely a meter registry that belongs to a child context. Instead, I think the closer should only close the beans from the current context and should only react to a close event that comes from that context. The beans can be retrieved using context.getBeansOfType(MeterRegistry.class).values(). Would you like to update your PR to this effect? If you'd prefer, feel free to open an issue instead and we can take things from here.

[berry120]

@wilkinsona Good point - I hadn't considered that. Now updated.

[wilkinsona]

Thanks for the updates, @berry120. I've merged the changes with a few modifications so that a child context's registries are still closed when the child is closed.