[Python-checkins] bpo-43688: Support the limited C API in debug mode (GH-25131)
vstinner
webhook-mailer at python.org
Fri Apr 2 09:45:45 EDT 2021
https://github.com/python/cpython/commit/3359cab038968935b40344fad7c30d211f9692e4
commit: 3359cab038968935b40344fad7c30d211f9692e4
branch: master
author: Victor Stinner <vstinner at python.org>
committer: vstinner <vstinner at python.org>
date: 2021-04-02T15:45:37+02:00
summary:
bpo-43688: Support the limited C API in debug mode (GH-25131)
The limited C API is now supported if Python is built in debug mode
(if the Py_DEBUG macro is defined). In the limited C API, the
Py_INCREF() and Py_DECREF() functions are now implemented as opaque
function calls, rather than accessing directly the PyObject.ob_refcnt
member, if Python is built in debug mode and the Py_LIMITED_API macro
targets Python 3.10 or newer. It became possible to support the
limited C API in debug mode because the PyObject structure is the
same in release and debug mode since Python 3.8 (see bpo-36465).
The limited C API is still not supported in the --with-trace-refs
special build (Py_TRACE_REFS macro).
files:
A Misc/NEWS.d/next/C API/2021-04-01-09-10-42.bpo-43688.G4gs6k.rst
M Doc/whatsnew/3.10.rst
M Include/object.h
M Objects/object.c
M PC/python3dll.c
M setup.py
diff --git a/Doc/whatsnew/3.10.rst b/Doc/whatsnew/3.10.rst
index a8ff56745c758..b84bcf93edb1e 100644
--- a/Doc/whatsnew/3.10.rst
+++ b/Doc/whatsnew/3.10.rst
@@ -1315,6 +1315,18 @@ New Features
to simulate.
(Contributed by Antoine Pitrou in :issue:`43356`.)
+* The limited C API is now supported if Python is built in debug mode (if the
+ ``Py_DEBUG`` macro is defined). In the limited C API, the :c:func:`Py_INCREF`
+ and :c:func:`Py_DECREF` functions are now implemented as opaque function
+ calls, rather than accessing directly the :c:member:`PyObject.ob_refcnt`
+ member, if Python is built in debug mode and the ``Py_LIMITED_API`` macro
+ targets Python 3.10 or newer. It became possible to support the limited C API
+ in debug mode because the :c:type:`PyObject` structure is the same in release
+ and debug mode since Python 3.8 (see :issue:`36465`).
+
+ The limited C API is still not supported in the ``--with-trace-refs`` special
+ build (``Py_TRACE_REFS`` macro).
+ (Contributed by Victor Stinner in :issue:`43688`.)
Porting to Python 3.10
----------------------
diff --git a/Include/object.h b/Include/object.h
index 14545839341f4..3138db0a0a3e4 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -54,11 +54,11 @@ whose size is determined when the object is allocated.
/* Py_DEBUG implies Py_REF_DEBUG. */
#if defined(Py_DEBUG) && !defined(Py_REF_DEBUG)
-#define Py_REF_DEBUG
+# define Py_REF_DEBUG
#endif
-#if defined(Py_LIMITED_API) && defined(Py_REF_DEBUG)
-#error Py_LIMITED_API is incompatible with Py_DEBUG, Py_TRACE_REFS, and Py_REF_DEBUG
+#if defined(Py_LIMITED_API) && defined(Py_TRACE_REFS)
+# error Py_LIMITED_API is incompatible with Py_TRACE_REFS
#endif
/* PyTypeObject structure is defined in cpython/object.h.
@@ -74,8 +74,8 @@ typedef struct _typeobject PyTypeObject;
#define _PyObject_EXTRA_INIT 0, 0,
#else
-#define _PyObject_HEAD_EXTRA
-#define _PyObject_EXTRA_INIT
+# define _PyObject_HEAD_EXTRA
+# define _PyObject_EXTRA_INIT
#endif
/* PyObject_HEAD defines the initial segment of every PyObject. */
@@ -427,21 +427,46 @@ PyAPI_FUNC(void) _Py_NegativeRefcount(const char *filename, int lineno,
PyAPI_FUNC(void) _Py_Dealloc(PyObject *);
+/*
+These are provided as conveniences to Python runtime embedders, so that
+they can have object code that is not dependent on Python compilation flags.
+*/
+PyAPI_FUNC(void) Py_IncRef(PyObject *);
+PyAPI_FUNC(void) Py_DecRef(PyObject *);
+
+// Similar to Py_IncRef() and Py_DecRef() but the argument must be non-NULL.
+// Private functions used by Py_INCREF() and Py_DECREF().
+PyAPI_FUNC(void) _Py_IncRef(PyObject *);
+PyAPI_FUNC(void) _Py_DecRef(PyObject *);
+
static inline void _Py_INCREF(PyObject *op)
{
+#if defined(Py_REF_DEBUG) && defined(Py_LIMITED_API) && Py_LIMITED_API+0 >= 0x030A0000
+ // Stable ABI for Python 3.10 built in debug mode.
+ _Py_IncRef(op);
+#else
+ // Non-limited C API and limited C API for Python 3.9 and older access
+ // directly PyObject.ob_refcnt.
#ifdef Py_REF_DEBUG
_Py_RefTotal++;
#endif
op->ob_refcnt++;
+#endif
}
#define Py_INCREF(op) _Py_INCREF(_PyObject_CAST(op))
static inline void _Py_DECREF(
-#ifdef Py_REF_DEBUG
+#if defined(Py_REF_DEBUG) && !(defined(Py_LIMITED_API) && Py_LIMITED_API+0 >= 0x030A0000)
const char *filename, int lineno,
#endif
PyObject *op)
{
+#if defined(Py_REF_DEBUG) && defined(Py_LIMITED_API) && Py_LIMITED_API+0 >= 0x030A0000
+ // Stable ABI for Python 3.10 built in debug mode.
+ _Py_DecRef(op);
+#else
+ // Non-limited C API and limited C API for Python 3.9 and older access
+ // directly PyObject.ob_refcnt.
#ifdef Py_REF_DEBUG
_Py_RefTotal--;
#endif
@@ -455,8 +480,9 @@ static inline void _Py_DECREF(
else {
_Py_Dealloc(op);
}
+#endif
}
-#ifdef Py_REF_DEBUG
+#if defined(Py_REF_DEBUG) && !(defined(Py_LIMITED_API) && Py_LIMITED_API+0 >= 0x030A0000)
# define Py_DECREF(op) _Py_DECREF(__FILE__, __LINE__, _PyObject_CAST(op))
#else
# define Py_DECREF(op) _Py_DECREF(_PyObject_CAST(op))
@@ -525,13 +551,6 @@ static inline void _Py_XDECREF(PyObject *op)
#define Py_XDECREF(op) _Py_XDECREF(_PyObject_CAST(op))
-/*
-These are provided as conveniences to Python runtime embedders, so that
-they can have object code that is not dependent on Python compilation flags.
-*/
-PyAPI_FUNC(void) Py_IncRef(PyObject *);
-PyAPI_FUNC(void) Py_DecRef(PyObject *);
-
// Create a new strong reference to an object:
// increment the reference count of the object and return the object.
PyAPI_FUNC(PyObject*) Py_NewRef(PyObject *obj);
diff --git a/Misc/NEWS.d/next/C API/2021-04-01-09-10-42.bpo-43688.G4gs6k.rst b/Misc/NEWS.d/next/C API/2021-04-01-09-10-42.bpo-43688.G4gs6k.rst
new file mode 100644
index 0000000000000..6b1d44ee17686
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2021-04-01-09-10-42.bpo-43688.G4gs6k.rst
@@ -0,0 +1,13 @@
+The limited C API is now supported if Python is built in debug mode (if the
+``Py_DEBUG`` macro is defined). In the limited C API, the :c:func:`Py_INCREF`
+and :c:func:`Py_DECREF` functions are now implemented as opaque function calls,
+rather than accessing directly the :c:member:`PyObject.ob_refcnt` member, if
+Python is built in debug mode and the ``Py_LIMITED_API`` macro targets Python
+3.10 or newer. It became possible to support the limited C API in debug mode
+because the :c:type:`PyObject` structure is the same in release and debug mode
+since Python 3.8 (see :issue:`36465`).
+
+The limited C API is still not supported in the ``--with-trace-refs`` special
+build (``Py_TRACE_REFS`` macro).
+
+Patch by Victor Stinner.
diff --git a/Objects/object.c b/Objects/object.c
index 0a8621b3503b3..0845966c5fe9d 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -13,6 +13,11 @@
#include "frameobject.h"
#include "interpreteridobject.h"
+#ifdef Py_LIMITED_API
+ // Prevent recursive call _Py_IncRef() <=> Py_INCREF()
+# error "Py_LIMITED_API macro must not be defined"
+#endif
+
#ifdef __cplusplus
extern "C" {
#endif
@@ -136,6 +141,18 @@ Py_DecRef(PyObject *o)
Py_XDECREF(o);
}
+void
+_Py_IncRef(PyObject *o)
+{
+ Py_INCREF(o);
+}
+
+void
+_Py_DecRef(PyObject *o)
+{
+ Py_DECREF(o);
+}
+
PyObject *
PyObject_Init(PyObject *op, PyTypeObject *tp)
{
diff --git a/PC/python3dll.c b/PC/python3dll.c
index 1567ac159168a..b5735e81e81ae 100644
--- a/PC/python3dll.c
+++ b/PC/python3dll.c
@@ -36,6 +36,8 @@ EXPORT_FUNC(_PyTrash_deposit_object)
EXPORT_FUNC(_PyTrash_destroy_chain)
EXPORT_FUNC(_PyTrash_thread_deposit_object)
EXPORT_FUNC(_PyTrash_thread_destroy_chain)
+EXPORT_FUNC(_Py_IncRef)
+EXPORT_FUNC(_Py_DecRef)
EXPORT_FUNC(Py_AddPendingCall)
EXPORT_FUNC(Py_AtExit)
EXPORT_FUNC(Py_BuildValue)
diff --git a/setup.py b/setup.py
index 75bd16375063a..3b4e7ae70a4ec 100644
--- a/setup.py
+++ b/setup.py
@@ -1864,17 +1864,11 @@ def detect_modules(self):
## # Uncomment these lines if you want to play with xxmodule.c
## self.add(Extension('xx', ['xxmodule.c']))
- if 'd' not in sysconfig.get_config_var('ABIFLAGS'):
- # Non-debug mode: Build xxlimited with limited API
- self.add(Extension('xxlimited', ['xxlimited.c'],
- define_macros=[('Py_LIMITED_API', '0x030a0000')]))
- self.add(Extension('xxlimited_35', ['xxlimited_35.c'],
- define_macros=[('Py_LIMITED_API', '0x03050000')]))
- else:
- # Debug mode: Build xxlimited with the full API
- # (which is compatible with the limited one)
- self.add(Extension('xxlimited', ['xxlimited.c']))
- self.add(Extension('xxlimited_35', ['xxlimited_35.c']))
+ # Limited C API
+ self.add(Extension('xxlimited', ['xxlimited.c'],
+ define_macros=[('Py_LIMITED_API', '0x030a0000')]))
+ self.add(Extension('xxlimited_35', ['xxlimited_35.c'],
+ define_macros=[('Py_LIMITED_API', '0x03050000')]))
def detect_tkinter_fromenv(self):
# Build _tkinter using the Tcl/Tk locations specified by
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