@Parallel not working for multiple factory beans

[tobiasschaefer]

Task List

• Steps to reproduce provided
• Stacktrace (if present) provided
• Example that reproduces the problem uploaded to Github
• Full description of the issue provided (see below)

Steps to Reproduce

1. Checkout https://github.com/tobiasschaefer/micronaut-parallel-bug
2. Start the application
3. Look at startup time shown in console, e.g. "Startup completed in 10999ms"

Expected Behaviour

In the class temp.Foo there are two factory beans, both annotated with @parallel and a Thread.sleep(5000).

I expect a startup time of a bit more that 5 seconds because both should be executed in parallel.

Actual Behaviour

I see a startup time of a bit more than 10 seconds.

@jameskleeh said "Yeah it looks like there is a synchronization block where there shouldn’t be
Can you file an issue?"

Environment Information

• Operating System: Linux
• Micronaut Version: 1.3.2 (current)
• JDK Version: 11.0.2

Example Application

https://github.com/tobiasschaefer/micronaut-parallel-bug

[jameskleeh]

Just FYI @Context will cause the beans to be loaded syncrhonously. @Parallel is by definition a context bean

[jameskleeh]

@graemerocher This is happening because the server looks up event listeners and thus has to wait for the other threads to unlock the singletonObjects. Any ideas?

[graemerocher]

Will have a look on Monday

[tobiasschaefer]

I've updated my example at https://github.com/tobiasschaefer/micronaut-parallel-bug by updating to 1.3.5 (and also tried 2.0.0.BUILD-SNAPSHOT). I also removed the @Context annotation as mentioned by @jameskleeh in the comments above.

All commits I've seen about this issue from @jameskleeh and @graemerocher are on branches. Is it more difficult that expected? Is there any way I can support you? I'd like to see a fix in 2.0.0.

[graemerocher]

I submitted a PR but the PR makes a compromise which may compromise the integrity of the application context. Essentially in order for beans to be allowed to be created in parallel we would need to not synchronize on the singletonObjects registry for creating beans annotated with @Parallel. If another bean in the dependency resolution graph also had a dependency on this bean then it is possible that you may end up with the bean being created twice due to the lack of synchronization which is clearly undesirable.

Since @Parallel is annotated with @Experimental right now we are debating the following options for Micronaut 2:

1. Allowing this compromise and documenting the risks
2. Deprecating and removing the feature completely

[tobiasschaefer]

@graemerocher : Thanks for that detailed response. I haven't got @Parallel to work at all, i.e. it was always sequential in all combinations I tried. The docs at https://docs.micronaut.io/latest/guide/index.html#builtInScopes are unfortunately very short and almost only reference the Javadoc.

Do you have an example where @Parallel actually works?

In my opinion @Parallel is a great feature considering we want to get the application up as fast as possible (btw, I like the idea of "If your bean fails to initialize in parallel then the application will be automatically shutdown." because it makes it even more powerful).

IMHO, it would be a pitty if this feature would be removed again.

[tobiasschaefer]

Hi @graemerocher , hi @jameskleeh ,

this issue is still open and relevant for me. It would probably make https://github.com/camunda-community-hub/micronaut-camunda-bpm have a faster startup time - which would be a nice added value compared to the available Spring Boot solution (especially when running a test-suite containing integration tests which might spin up the application multiple times).

To recap the problem: I have two beans which are both annotated with @Parallel whose initialization takes 5 seconds each. I want the application to start in about 5 seconds, not 10 seconds.

I've recreated a simple example based on Micronaut 3.3.0, see https://github.com/tobiasschaefer/micronaut-parallel-bug-mn330

I've simplified the example to use simple beans instead of factory beans and it is based on the code from your test-suite at https://github.com/micronaut-projects/micronaut-core/blob/3.3.x/inject-java/src/test/groovy/io/micronaut/inject/parallel/ParallelBean.java

I know that @Parallel is marked as @Experimental but IMHO it is not working at all.

In https://github.com/micronaut-projects/micronaut-core/blob/3.3.x/inject/src/main/java/io/micronaut/context/DefaultBeanContext.java#L2463 there is a synchronization which prevents the parallel execution: (I think @jameskleeh is referring to that in his comment)

synchronized (singletonObjects) {
    loadContextScopeBean(beanDefinition);
}

What is your opinion on this? Can you provide a working example where beans are actually initialized in parallel?