Signed-off-by: YangKeao yangkeao@chunibyo.icu

What problem does this PR solve?

Issue Number: close #38378

Problem Summary:

The set/get hook of variables should be able to call asynchronous functions, which should be protected by a context.Context to be able to kill/timeout...

What is changed and how it works?

1. Add ctx context.Context for SetGlobal/GetGlobal definition.
2. Add this paramater to every function which calls the SetGlobal/GetGlobal, and do this step recursively...
3. Some get/set with a specified variable name, which we know will not use the ctx, will be passed a context.Background() directly.
4. Some context.TODO() in the middle way are modified to the correct context.

I have considered several different approches to not bring in such a big change:

1. Distinguish the hook with / without the context. However, the setter/getter will always need a context (or implicitly pass a context.Background(). It will not solve any problem, but leave some context.Background() in some hidden paths.
2. Use a new function to call without context. For example, have two functions: SetGlobalFromHook and SetGlobalFromHookWithoutContext, and implement the second with SetGlobalFromHook(context.Background(), ...). But I realized that SetGlobalFromHookWithoutContext( has no difference with SetGlobalFromHook(context.Background(), then I prefer to use the argument directly.

If you have better idea to pass in the context, without so many changes, please leave comments 😃 . Or you think it's not necessary, and use a newly created context with deadline is good enough, please also tells your opinion under this PR.