update to slf4j, remove DynamicLog

[chuxi]

What do these changes do?

DynamicLog implementation impact the ray java performance badly. Many string concat in DynamicLog and it is based on log4j 1.2. To decouple from concrete log tool, use slf4j instead.

Here is the first step to complete the whole work. It removed the DynamicLog and keep its original functions by calling System.setProperty() before Ray core log starts. Because it requires to support multi-workers processes logging. To tell apart each worker's log, it requires to set different names for the worker's log.

And in the future, any logging should use parameter instead of string concat.

// the right way
String name = "tom";
logger.info("hello {}", name); 

// wrong way
logger.info("hello " + name);

Related issue number

N/A

[AmplabJenkins]

Test FAILed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/Ray-PRB/6598/
Test FAILed.

[chuxi]

anybody can help review the pull request?

[pcmoritz]

@eric-jj @raulchen Can you help review this or suggest somebody for review?

[raulchen]

@pcmoritz we've already reviewed this at antgroup#46.
I think it should be good to merge.
(Actually all PRs from Ant are internally reviewed at ant-tech-alliance/ray repo before pushing to ray-project/ray)

[robertnishihara]

@raulchen I see, I would strongly consider doing the reviewing on this repository instead. That way we can see the issues/considerations that were discussed.

If the concern is that it would cause too much clutter, I think it's worth it to provide more visibility.

[pcmoritz]

Great, thanks! The changes look good to me too.

[pcmoritz]

(I second @robertnishihara's comment, it will be better for us and the other open source developers to have the reviews here. Also you shouldn't worry about posting half-finished PRs that are still being worked on here, that's completely fine.)

[raulchen]

@robertnishihara @pcmoritz Thanks for the feedback!

The main purpose of our internal reviews is to ensure a baseline of code quality, and avoid people accidentally violating company's open-source policy.

But I agree that it'd be worth it to share what was discussed before with you. That will help you review faster. I think, in the future, we can also link the original PR. Does this sounds good to you?

[chuxi]

Yes. I should also post the pull request in ant-ray. Thanks for reviewing the pr.