[Refcator] Extract message types as MessageType Enum in ProcessEnvironment

[breakds]

This is a refactor, which means that no logic is being changed.

Motivation

This is part of the effort to address #913. A sub-task requires extract the worker logic to be out of the class (for some reason it will prevent multiprocessing to work correctly). Without such change the multiprocessing.Process will just be stuck on start().

[emailweixu]

This is a refactor, which means that no logic is being changed.

Motivation

This is part of the effort to address #913. A sub-task requires extract the worker logic to be out of the class (for some reason it will prevent multiprocessing to work correctly). Without such change the multiprocessing.Process will just be stuck on start().

How does this change solve the problem of stucking on start()?

[breakds]

This is a refactor, which means that no logic is being changed.

Motivation

This is part of the effort to address #913. A sub-task requires extract the worker logic to be out of the class (for some reason it will prevent multiprocessing to work correctly). Without such change the multiprocessing.Process will just be stuck on start().

How does this change solve the problem of stucking on start()?

I do not know why as well, this is just an observation. My guess is that without passing self the multiprocessing do not have to pickle the ProcessEnvironment itself, which might be triggering something that contribute to the "getting stuck" problem.