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bpo-45953: Statically allocate the main interpreter (and initial thread state). (gh-29883)

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Previously, the main interpreter was allocated on the heap during runtime initialization.  Here we instead embed it into _PyRuntimeState, which means it is statically allocated as part of the _PyRuntime global.  The same goes for the initial thread state (of each interpreter, including the main one).  Consequently there are fewer allocations during runtime/interpreter init, fewer possible failures, and better memory locality.

FYI, this also helps efforts to consolidate globals, which in turns helps work on subinterpreter isolation.

https://bugs.python.org/issue45953
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Eric Snow 2022-01-12 16:28:46 -07:00 • committed by GitHub
parent 0bbf30e2b9
commit ed57b36c32
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8 changed files with 115 additions and 34 deletions
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48
Include/internal/pycore_runtime.h
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@ -11,8 +11,10 @@ extern "C" {
#include "pycore_atomic.h" /* _Py_atomic_address */
#include "pycore_gil.h" // struct _gil_runtime_state
#include "pycore_global_objects.h" // struct _Py_global_objects
#include "pycore_interp.h" // struct _is
#include "pycore_unicodeobject.h" // struct _Py_unicode_runtime_ids
/* ceval state */
struct _ceval_runtime_state {
@ -53,6 +55,9 @@ typedef struct _Py_AuditHookEntry {
/* Full Python runtime state */
/* _PyRuntimeState holds the global state for the CPython runtime.
That data is exposed in the internal API as a static variable (_PyRuntime).
*/
typedef struct pyruntimestate {
/* Has been initialized to a safe state.
@ -81,7 +86,11 @@ typedef struct pyruntimestate {
struct pyinterpreters {
PyThread_type_lock mutex;
/* The linked list of interpreters, newest first. */
PyInterpreterState *head;
/* The runtime's initial interpreter, which has a special role
in the operation of the runtime. It is also often the only
interpreter. */
PyInterpreterState *main;
/* _next_interp_id is an auto-numbered sequence of small
integers. It gets initialized in _PyInterpreterState_Init(),
@ -118,25 +127,44 @@ typedef struct pyruntimestate {
struct _Py_unicode_runtime_ids unicode_ids;
/* All the objects that are shared by the runtime's interpreters. */
struct _Py_global_objects global_objects;
// If anything gets added after global_objects then
// _PyRuntimeState_reset() needs to get updated to clear it.
/* The following fields are here to avoid allocation during init.
The data is exposed through _PyRuntimeState pointer fields.
These fields should not be accessed directly outside of init.
All other _PyRuntimeState pointer fields are populated when
needed and default to NULL.
For now there are some exceptions to that rule, which require
allocation during init. These will be addressed on a case-by-case
basis. Most notably, we don't pre-allocated the several mutex
(PyThread_type_lock) fields, because on Windows we only ever get
a pointer type.
*/
/* PyInterpreterState.interpreters.main */
PyInterpreterState _main_interpreter;
} _PyRuntimeState;
#define _PyThreadState_INIT \
{ \
._static = 1, \
}
#define _PyInterpreterState_INIT \
{ \
._static = 1, \
._initial_thread = _PyThreadState_INIT, \
}
#define _PyRuntimeState_INIT \
{ \
.global_objects = _Py_global_objects_INIT, \
._main_interpreter = _PyInterpreterState_INIT, \
}
/* Note: _PyRuntimeState_INIT sets other fields to 0/NULL */
static inline void
_PyRuntimeState_reset(_PyRuntimeState *runtime)
{
/* Make it match _PyRuntimeState_INIT. */
memset(runtime, 0, (size_t)&runtime->global_objects - (size_t)runtime);
_Py_global_objects_reset(&runtime->global_objects);
}
/* other API */
PyAPI_DATA(_PyRuntimeState) _PyRuntime;