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gh-84436: Implement Immortal Objects (gh-19474)

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This is the implementation of PEP683

Motivation:

The PR introduces the ability to immortalize instances in CPython which bypasses reference counting. Tagging objects as immortal allows up to skip certain operations when we know that the object will be around for the entire execution of the runtime.

Note that this by itself will bring a performance regression to the runtime due to the extra reference count checks. However, this brings the ability of having truly immutable objects that are useful in other contexts such as immutable data sharing between sub-interpreters.
This commit is contained in:
Eddie Elizondo 2023-04-22 15:39:37 -04:00 • committed by GitHub
parent 916de04fd1
commit ea2c001650
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GPG key ID: 4AEE18F83AFDEB23
35 changed files with 483 additions and 171 deletions
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48
Include/internal/pycore_object.h
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@ -14,21 +14,25 @@ extern "C" {
#include "pycore_pystate.h" // _PyInterpreterState_GET()
#include "pycore_runtime.h" // _PyRuntime
/* This value provides *effective* immortality, meaning the object should never
be deallocated (until runtime finalization). See PEP 683 for more details about
immortality, as well as a proposed mechanism for proper immortality. */
#define _PyObject_IMMORTAL_REFCNT 999999999
#define _PyObject_IMMORTAL_INIT(type) \
{ \
.ob_refcnt = _PyObject_IMMORTAL_REFCNT, \
.ob_type = (type), \
}
#define _PyVarObject_IMMORTAL_INIT(type, size) \
{ \
.ob_base = _PyObject_IMMORTAL_INIT(type), \
.ob_size = size, \
}
/* We need to maintain an internal copy of Py{Var}Object_HEAD_INIT to avoid
designated initializer conflicts in C++20. If we use the deinition in
object.h, we will be mixing designated and non-designated initializers in
pycore objects which is forbiddent in C++20. However, if we then use
designated initializers in object.h then Extensions without designated break.
Furthermore, we can't use designated initializers in Extensions since these
are not supported pre-C++20. Thus, keeping an internal copy here is the most
backwards compatible solution */
#define _PyObject_HEAD_INIT(type) \
{ \
_PyObject_EXTRA_INIT \
.ob_refcnt = _Py_IMMORTAL_REFCNT, \
.ob_type = (type) \
},
#define _PyVarObject_HEAD_INIT(type, size) \
{ \
.ob_base = _PyObject_HEAD_INIT(type) \
.ob_size = size \
},
PyAPI_FUNC(void) _Py_NO_RETURN _Py_FatalRefcountErrorFunc(
const char *func,
@ -61,9 +65,20 @@ static inline void _Py_RefcntAdd(PyObject* op, Py_ssize_t n)
}
#define _Py_RefcntAdd(op, n) _Py_RefcntAdd(_PyObject_CAST(op), n)
static inline void _Py_SetImmortal(PyObject *op)
{
if (op) {
op->ob_refcnt = _Py_IMMORTAL_REFCNT;
}
}
#define _Py_SetImmortal(op) _Py_SetImmortal(_PyObject_CAST(op))
static inline void
_Py_DECREF_SPECIALIZED(PyObject *op, const destructor destruct)
{
if (_Py_IsImmortal(op)) {
return;
}
_Py_DECREF_STAT_INC();
#ifdef Py_REF_DEBUG
_Py_DEC_REFTOTAL(_PyInterpreterState_GET());
@ -82,6 +97,9 @@ _Py_DECREF_SPECIALIZED(PyObject *op, const destructor destruct)
static inline void
_Py_DECREF_NO_DEALLOC(PyObject *op)
{
if (_Py_IsImmortal(op)) {
return;
}
_Py_DECREF_STAT_INC();
#ifdef Py_REF_DEBUG
_Py_DEC_REFTOTAL(_PyInterpreterState_GET());