RFC: abstract taskState and globalState

[wangbj]

As discussed before, there're per-task state (state.hpp) as well as global state (globalState.hpp), most of them, however, exist because of stat* families, if we no longer need them because of detfs, them most of the states can be eliminated.

Because we might end up with sharing pages for per-task state / global state, the states should implement Serialize instance.

Here's a brief review:

• For global states, we can keep the statistics, and global time;
• For per-task states, we may keep the logger (per-task instead of global), signal handlers;

Since we already have injected mmap pages, we can desinate several pages for per-task states, and they should be private (non-sharable pages); The global states doesn't have much crucial data except for global time, and we might not need a shared global page after all, instead, we can have few APIs to retrieve global time, and/or update the statistics.

[gatoWololo]

I agree, one of the motivations behind the detfs layer is to omit all these stat* functions we need to intercept. So a good chunk of global state will be gone, as you stated, at some point we will probably need some global state.

I agree with what you have here. One thing to note is once we move to logical clocks, that will probably be more global state to share with the central coordinator?