Describe the problem

Currently, ray/worker.py seems too heavy. It contains ~3000 lines of code (maybe 1/3 of core python code of ray).

And its a bit messy (contains nearly all kinds of structure-breaking reference🙃) :

global_worker = Worker()

class Worker:
    def func_a(self):
        foo(worker=self)
        
    def func_b(self):
        foo()
        
    def func_c(self):
        put()

    def func_d(self):
        bar(worker=self)

    def func_d(self):
        bar(worker=global_worker)

def foo(worker=global_worker):
    pass

def bar(worker):
    pass

def put():
    do_something(global_worker)

What's more, worker.py contains all these things:

• logging utils
• serialization utils
• core worker logics
• ray APIs
• ray exceptions
• constants

Since a possible correct dependency may look like:

, it could be better to divide worker.py into several independent modules. We could keep ray's APIs in worker.py so it may not affect other parts of ray.

I want to know if a PR for refactoring worker.py is welcomed? (I understand that such a PR is heavy and may be unnecessary now.)