[Improvement] Improve GravitinoCatalogManager close method

[justinmclean]

What would you like to be improved?

GravitinoCatalogManager's close method mixes static and volatile variables in a nonstatic method and that may cause issues. Correctly updating a static field from a non-static method can be tricky to get right and could easily lead to bugs if there are multiple threads.

How should we improve?

See if this can be improved to be more thread safe.

[xiaozcy]

I created a PR(#3096) for this, could you take a look at it?

[FANNG1]

it's not supposed to work in the multi-thread environment, so I prefer not to change it.

[justinmclean]

Is the fact that it won't work in a multi-thread environment documented anywhere? That seems like an omission that a user would want to know about.

[FANNG1]

There is no document for this, maybe we could add some comment to the class file, WDYT?

[yuqi1129]

See if this can be improved to be more thread safe.

Is there a need to support multi-threading? It currently does not support multi-threading.

[justinmclean]

Perhaps I'm misisng something, but I assume users expect this to support muti-threading.

[shaofengshi]

I agree with Justin, we couldn't stop user/client (especially it is a flink connector) from using it in multi-threading, so the code should be robust, especially that is too complex to achieve.