Starter point: PEP 554 – Multiple Interpreters in the Stdlib.
The goal is to support running multiple Python interpreters in parallel with
one lock per interpreter (no more “Global Interpreter Lock”, but one
“Interpreter Lock” per interpreter). An interpreter would only be able to run
one Python thread holding the interpreter lock at the same time, but multiple
Python threads which released the interpreter lock (ex: to call a system call
like read()) can be run in parallel.
To maximize performances, shared states between interpreters must be minimized. Each share state must be carefully protected by a lock, which prevent to run code in parallel.
During Python 3.7 and 3.8 dev cycle, Eric Snow moved scattered core global
variables into a _PyRuntimeState structure which has a single global and shared
instance: _PyRuntime.
Most functions access directly to _PyRuntime, directly or indirectly:
PyThreadState *tstate = _PyThreadState_GET(); access implicitly
_PyRuntime.
PyThreadState *tstate = _PyRuntimeState_GetThreadState(&_PyRuntime); gets
access explicitly _PyRuntime. Get runtime->gilstate.tstate_current.
_PyRuntimeState fields:
ceval
exitfuncs, nexitfuncs
finalizing
gc
gilstate
interpreters
main_thread
open_code_hook, open_code_userdata, audit_hook_head
pre_initialized, core_initialized, initialized
preconfig
xidregistry
Move _PyRuntimeState.gilstate to PyInterpreterState:
Remove _PyRuntimeState_GetThreadState()
Update _PyThreadState_GET()
Move most _PyRuntimeState fields into PyInterpreterState
Pass the “context” to private C functions: the context can be _PyRuntime,
a field of _PyRuntime, the Python thread state (tstate), etc.
Functions of public C API must not be modified at this stage to add new “context” parameters. Only the internal C API can be modified.
Get the current Python thread:
_PyRuntimeState_GetThreadState(&_PyRuntime). WIP: gilstate must
move to PyInterpreterState
Get the current interpreter: tstate->interp.
PyInterpreterState moved to the internal C API
_PyRuntimeState structure and _PyRuntime variable created