Use member non-pointer declarations in Py*State structs instead of heap-allocated pointers.

[ericsnowcurrently]

(See #177.)

The full runtime state of a cpython process is found in PyRuntimeState, PyInterpreterState, and PyThreadState(and, for now, a bunch of static variables), which currently form a single tree at runtime under the_PyRuntime` global variable. Currently these three structs hold many pointers, which are (allocated and) populated during runtime initialization.

For most of the pointers we could instead replace them with static declarations (of the the corresponding data) in the relevant Py*State structs. (This wouldn't work for any variables where the size isn't fixed at compile time (e.g. PyVarObject) but it should work for most.)

Structure

struct pyruntimestate {  # _PyRuntimeState
    struct _Py_global_objects {
        struct {
        } singletons;
        struct {
        } freelists;
    } global_objects;
};

struct _is {  # PyInterpreterState
    struct _Py_global_objects {
        struct {
        } singletons;
        struct {
        } freelists;
        struct {
        } caches;
    } global_objects;
};

TODO

Note that this only covers the current members of _PyRuntimeState, PyInterpreterState, and PyThreadState. Current static globals will be dealt with separately.

• consolidate global objects
  • singletons
    • [global objects] static allocation/init for the small ints #179
    • fold _Py_bytes_state into _PyRuntimeState.global_objects.singletons #180
    • move _Py_unicode_state.empty_string and _Py_unicode_state.latin1 into _PyRuntimeState.global_objects.singletons
    • move _Py_unicode_state.ids (_Py_Identifier) into _PyRuntimeState.global_objects.singletons #198
    • move _Py_exc_state.errnomap and _Py_exc_state.PyExc_ExceptionGroup into _PyRuntimeState.global_objects.singletons
    • fold _Py_ast_state into _PyRuntimeState.global_objects.singletons
  • free lists
    • move _Py_exc_state.memerrors_freelist to _PyRuntimeState.global_objects.freelists.memory_errors
    • move PyInterpreterState.float_state to PyInterpreterState.global_objects.freelists.float`
    • move PyInterpreterState.tuple_state to PyInterpreterState.global_objects.freelists.tuple`
    • move PyInterpreterState.list_state to PyInterpreterState.global_objects.freelists.list`
    • move PyInterpreterState.dict_state to PyInterpreterState.global_objects.freelists.dict`
    • move PyInterpreterState.async_gen_state to PyInterpreterState.global_objects.freelists.async_gen`
    • move PyInterpreterState.context_state to PyInterpreterState.global_objects.freelists.context`
    • move PyInterpreterState.slice_cache to PyInterpreterState.global_objects.freelists`
    • [ ]
  • caches
    • move PyInterpreterState.type_cache to _PyRuntimeState.global_objects.caches.type_attrs`
    • move _Py_unicode_state.interned into PyInterpreterState.global_objects.caches
• statically allocate (and initialize) the top-level structures #178
  • _PyRuntimeState.interpreters.main
  • the initial per-interpreter PyThreadState
• add structure and helpers
  • add _PyRuntimeState.global_objects and helpers
  • add _PyRuntimeState.global_objects.singletons and helpers
  • add _PyRuntimeState.global_objects.freelists and helpers
  • add _PyRuntimeState.global_objects.caches and helpers
  • add helpers for statically allocating/initializing a string
  • add helpers for statically allocating/initializing a dict
  • add helpers for statically allocating/initializing a list
• statically allocate objects
  • singletons
  • free lists
  • caches
  • state
    • PyInterpreterState.modules (dict)
    • PyInterpreterState.modules_by_index (list)
    • PyInterpreterState.sysdict (dict)
    • PyInterpreterState.builtins (dict)
    • PyInterpreterState.importlib (dict)
    • PyInterpreterState.codec_search_path (list)
    • PyInterpreterState.codec_search_cache (dict)
    • PyInterpreterState.codec_error_registry (dict)
    • PyInterpreterState.dict (dict)
    • PyInterpreterState.warnings.filters (list)
    • PyInterpreterState.warnings.once_registry (dict)
    • PyInterpreterState.gc.trash_delete_later (list)
    • PyInterpreterState.gc.garbage (list)
    • PyInterpreterState.gc.callbacks (list)
    • PyInterpreterState.audit_hooks (list)
    • PyThreadState.dict (dict)
    • PyThreadState.trash_delete_later (list)
• statically allocate non-object state (?)

[gvanrossum]

This sounds like an Epic, right? Many of the subtasks are worthy of being separate PRs and hence separate issues, according to our new approach to the Project board.

[ericsnowcurrently]

Correct. I added the "Epic" label.

[ericsnowcurrently]

The changes so far have had almost zero impact on performance. So I'm probably going to table this overall effort. (It's worth doing for other reasons, but not for improving performance.) However, there may be a few specific parts that are worth doing. I'll create separate tasks for any of those.

[ericsnowcurrently]

I'm closing this as it's so low priority at this point that it doesn't need to be on our board.