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Commit ca54c2f4 authored by Tim Peters's avatar Tim Peters
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Moving pymalloc along. 

As threatened, PyMem_{Free, FREE} also invoke the object deallocator now
when pymalloc is enabled (well, it does when pymalloc isn't enabled too,
but in that case "the object deallocator" is plain free()).

This is maximally backward-compatible, but it leaves a bitter aftertaste.

Also massive reworking of comments.
parent 4bb67e61
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Include/objimpl.h
View file @ ca54c2f4
/* The PyObject_ memory family: high-level object memory interfaces.
See pymem.h for the low-level PyMem_ family.
*/
#ifndef Py_OBJIMPL_H
#define Py_OBJIMPL_H
......@@ -8,82 +11,89 @@
extern "C" {
#endif
/* BEWARE:
Each interface exports both functions and macros. Extension modules should
use the functions, to ensure binary compatibility across Python versions.
Because the Python implementation is free to change internal details, and
the macros may (or may not) expose details for speed, if you do use the
macros you must recompile your extensions with each Python release.
Never mix calls to PyObject_ memory functions with calls to the platform
malloc/realloc/ calloc/free, or with calls to PyMem_.
*/
/*
Functions and macros for modules that implement new object types.
You must first include "object.h".
- PyObject_New(type, typeobj) allocates memory for a new object of
the given type; here 'type' must be the C structure type used to
represent the object and 'typeobj' the address of the corresponding
type object. Reference count and type pointer are filled in; the
rest of the bytes of the object are *undefined*! The resulting
expression type is 'type *'. The size of the object is determined
by the tp_basicsize field of the type object.
- PyObject_NewVar(type, typeobj, n) is similar but allocates a
variable-size object with n extra items. The size is computed as
tp_basicsize plus n * tp_itemsize. This fills in the ob_size field
as well.
- PyObject_Del(op) releases the memory allocated for an object. It
does not run a destructor -- it only frees the memory. PyObject_Free
is identical.
- PyObject_Init(op, typeobj) and PyObject_InitVar(op, typeobj, n) are
similar to PyObject_{New, NewVar} except that they don't allocate
the memory needed for an object. Instead of the 'type' parameter,
they accept the pointer of a new object (allocated by an arbitrary
allocator) and initialize its object header fields.
Note that objects created with PyObject_{New, NewVar} are allocated
using the specialized Python allocator (implemented in obmalloc.c), if
WITH_PYMALLOC is enabled. In addition, a special debugging allocator
is used if PYMALLOC_DEBUG is also #defined.
In case a specific form of memory management is needed, implying that
the objects would not reside in the Python heap (for example standard
malloc heap(s) are mandatory, use of shared memory, C++ local storage
or operator new), you must first allocate the object with your custom
allocator, then pass its pointer to PyObject_{Init, InitVar} for
filling in its Python-specific fields: reference count, type pointer,
possibly others. You should be aware that Python has very limited
control over these objects because they don't cooperate with the
Python memory manager. Such objects may not be eligible for automatic
garbage collection and you have to make sure that they are released
accordingly whenever their destructor gets called (cf. the specific
- PyObject_New(type, typeobj) allocates memory for a new object of the given
type, and initializes part of it. 'type' must be the C structure type used
to represent the object, and 'typeobj' the address of the corresponding
type object. Reference count and type pointer are filled in; the rest of
the bytes of the object are *undefined*! The resulting expression type is
'type *'. The size of the object is determined by the tp_basicsize field
of the type object.
- PyObject_NewVar(type, typeobj, n) is similar but allocates a variable-size
object with room for n items. In addition to the refcount and type pointer
fields, this also fills in the ob_size field.
- PyObject_Del(op) releases the memory allocated for an object. It does not
run a destructor -- it only frees the memory. PyObject_Free is identical.
- PyObject_Init(op, typeobj) and PyObject_InitVar(op, typeobj, n) don't
allocate memory. Instead of a 'type' parameter, they take a pointer to a
new object (allocated by an arbitrary allocator), and initialize its object
header fields.
Note that objects created with PyObject_{New, NewVar} are allocated using the
specialized Python allocator (implemented in obmalloc.c), if WITH_PYMALLOC is
enabled. In addition, a special debugging allocator is used if PYMALLOC_DEBUG
is also #defined.
In case a specific form of memory management is needed (for example, if you
must use the platform malloc heap(s), or shared memory, or C++ local storage or
operator new), you must first allocate the object with your custom allocator,
then pass its pointer to PyObject_{Init, InitVar} for filling in its Python-
specific fields: reference count, type pointer, possibly others. You should
be aware that Python no control over these objects because they don't
cooperate with the Python memory manager. Such objects may not be eligible
for automatic garbage collection and you have to make sure that they are
released accordingly whenever their destructor gets called (cf. the specific
form of memory management you're using).
Unless you have specific memory management requirements, it is
recommended to use PyObject_{New, NewVar, Del}. */
Unless you have specific memory management requirements, use
PyObject_{New, NewVar, Del}.
*/
/*
* Raw object memory interface
* ===========================
*/
/* The use of this API should be avoided, unless a builtin object
constructor inlines PyObject_{New, NewVar}, either because the
latter functions cannot allocate the exact amount of needed memory,
either for speed. This situation is exceptional, but occurs for
some object constructors (PyBuffer_New, PyList_New...). Inlining
PyObject_{New, NewVar} for objects that are supposed to belong to
the Python heap is discouraged. If you really have to, make sure
the object is initialized with PyObject_{Init, InitVar}. Do *not*
inline PyObject_{Init, InitVar} for user-extension types or you
might seriously interfere with Python's memory management. */
/* Functions */
/* Functions to call the same malloc/realloc/free as used by Python's
object allocator. If WITH_PYMALLOC is enabled, these may differ from
the platform malloc/realloc/free. The Python object allocator is
designed for fast, cache-conscious allocation of many "small" objects,
with low hidden memory overhead. PyObject_Malloc(0) returns a unique
non-NULL pointer if possible. PyObject_Realloc(NULL, n) acts like
PyObject_Malloc(n). PyObject_Realloc(p != NULL, 0) does not return
NULL or free the memory at p. Returned pointers must be checked for
NULL explicitly; no action is performed on failure other than to return
NULL. */
and with low hidden memory overhead.
PyObject_Malloc(0) returns a unique non-NULL pointer if possible.
PyObject_Realloc(NULL, n) acts like PyObject_Malloc(n).
PyObject_Realloc(p != NULL, 0) does not return NULL, or free the memory
at p.
Returned pointers must be checked for NULL explicitly; no action is
performed on failure other than to return NULL (no warning it printed, no
exception is set, etc).
For allocating objects, use PyObject_{New, NewVar} instead whenever
possible. The PyObject_{Malloc, Realloc, Free} family is exposed
so that you can exploit Python's small-block allocator for non-object
uses. If you must use these routines to allocate object memory, make sure
the object gets initialized via PyObject_{Init, InitVar} after obtaining
the raw memory.
*/
extern DL_IMPORT(void *) PyObject_Malloc(size_t);
extern DL_IMPORT(void *) PyObject_Realloc(void *, size_t);
extern DL_IMPORT(void) PyObject_Free(void *);
......@@ -114,7 +124,12 @@ DL_IMPORT(void) _PyObject_DebugMallocStats(void);
#else /* ! WITH_PYMALLOC */
#define PyObject_MALLOC PyMem_MALLOC
#define PyObject_REALLOC PyMem_REALLOC
#define PyObject_FREE PyMem_FREE
/* This is an odd one! For backward compatability with old extensions, the
PyMem "release memory" functions have to invoke the object allocator's
free() function. When pymalloc isn't enabled, that leaves us using
the platform free(). */
#define PyObject_FREE free
#endif /* WITH_PYMALLOC */
#define PyObject_Del PyObject_Free
......@@ -196,9 +211,7 @@ extern DL_IMPORT(PyVarObject *) _PyObject_NewVar(PyTypeObject *, int);
if (op == NULL)
return PyErr_NoMemory();
op = PyObject_Init(op, &YourTypeStruct);
if (op == NULL)
return NULL;
PyObject_Init(op, &YourTypeStruct);
op->ob_field = value;
...
......@@ -207,7 +220,8 @@ extern DL_IMPORT(PyVarObject *) _PyObject_NewVar(PyTypeObject *, int);
Note that in C++, the use of the new operator usually implies that
the 1st step is performed automatically for you, so in a C++ class
constructor you would start directly with PyObject_Init/InitVar. */
constructor you would start directly with PyObject_Init/InitVar
*/
/*
* Garbage Collection Support
......@@ -234,7 +248,7 @@ extern DL_IMPORT(PyVarObject *) _PyObject_GC_Resize(PyVarObject *, int);
#ifdef WITH_CYCLE_GC
/* GC information is stored BEFORE the object structure */
/* GC information is stored BEFORE the object structure. */
typedef union _gc_head {
struct {
union _gc_head *gc_next; /* not NULL if object is tracked */
......
Include/pymem.h
View file @ ca54c2f4
/* Lowest-level memory allocation interface */
/* The PyMem_ family: low-level memory allocation interfaces.
See objimpl.h for the PyObject_ memory family.
*/
#ifndef Py_PYMEM_H
#define Py_PYMEM_H
......@@ -12,37 +13,39 @@ extern "C" {
/* BEWARE:
Each interface exports both functions and macros. Extension modules
should normally use the functions for ensuring binary compatibility
of the user's code across Python versions. Subsequently, if the
Python runtime switches to its own malloc (different from standard
malloc), no recompilation is required for the extensions.
The macro versions are free to trade compatibility for speed, although
there's no guarantee they're ever faster. Extensions shouldn't use the
macro versions, as they don't gurantee binary compatibility across
releases.
Do not mix calls to PyMem_xyz with calls to platform
malloc/realloc/calloc/free. */
Each interface exports both functions and macros. Extension modules should
use the functions, to ensure binary compatibility across Python versions.
Because the Python implementation is free to change internal details, and
the macros may (or may not) expose details for speed, if you do use the
macros you must recompile your extensions with each Python release.
Never mix calls to PyMem_ with calls to the platform malloc/realloc/
calloc/free. For example, on Windows different DLLs may end up using
different heaps, and if you use PyMem_Malloc you'll get the memory from the
heap used by the Python DLL; it could be a disaster if you free()'ed that
directly in your own extension. Using PyMem_Free instead ensures Python
can return the memory to the proper heap. As another example, in
PYMALLOC_DEBUG mode, Python wraps all calls to all PyMem_ and PyObject_
memory functions in special debugging wrappers that add additional
debugging info to dynamic memory blocks. The system routines have no idea
what to do with that stuff, and the Python wrappers have no idea what to do
with raw blocks obtained directly by the system routines then.
*/
/*
* Raw memory interface
* ====================
*/
/* Functions */
/* Functions
/* Functions supplying platform-independent semantics for malloc/realloc/
free; useful if you need to be sure you're using the same memory
allocator as Python (this can be especially important on Windows, if
you need to make sure you're using the same MS malloc/free, and out of
the same heap, as the main Python DLL uses).
These functions make sure that allocating 0 bytes returns a distinct
Functions supplying platform-independent semantics for malloc/realloc/
free. These functions make sure that allocating 0 bytes returns a distinct
non-NULL pointer (whenever possible -- if we're flat out of memory, NULL
may be returned), even if the platform malloc and realloc don't.
Returned pointers must be checked for NULL explicitly. No action is
performed on failure (no exception is set, no warning is printed, etc).` */
performed on failure (no exception is set, no warning is printed, etc).
*/
extern DL_IMPORT(void *) PyMem_Malloc(size_t);
extern DL_IMPORT(void *) PyMem_Realloc(void *, size_t);
......@@ -56,7 +59,6 @@ extern DL_IMPORT(void) PyMem_Free(void *);
/* Redirect all memory operations to Python's debugging allocator. */
#define PyMem_MALLOC PyObject_MALLOC
#define PyMem_REALLOC PyObject_REALLOC
#define PyMem_FREE PyObject_FREE
#else /* ! PYMALLOC_DEBUG */
......@@ -65,40 +67,43 @@ extern DL_IMPORT(void) PyMem_Free(void *);
#else
#define PyMem_MALLOC malloc
#endif
/* Caution: whether MALLOC_ZERO_RETURNS_NULL is #defined has nothing to
do with whether platform realloc(non-NULL, 0) normally frees the memory
or returns NULL. Rather than introduce yet another config variation,
just make a realloc to 0 bytes act as if to 1 instead. */
#define PyMem_REALLOC(p, n) realloc((p), (n) ? (n) : 1)
#define PyMem_FREE free
#endif /* PYMALLOC_DEBUG */
/* In order to avoid breaking old code mixing PyObject_{New, NEW} with
PyMem_{Del, DEL} and PyMem_{Free, FREE}, the PyMem "release memory"
functions have to be redirected to the object deallocator. */
#define PyMem_FREE PyObject_FREE
/*
* Type-oriented memory interface
* ==============================
*
* These are carried along for historical reasons. There's rarely a good
* reason to use them anymore.
* reason to use them anymore (you can just as easily do the multiply and
* cast yourself).
*/
/* Functions */
#define PyMem_New(type, n) \
( (type *) PyMem_Malloc((n) * sizeof(type)) )
#define PyMem_Resize(p, type, n) \
( (p) = (type *) PyMem_Realloc((p), (n) * sizeof(type)) )
/* In order to avoid breaking old code mixing PyObject_{New, NEW} with
PyMem_{Del, DEL} (there was no choice about this in 1.5.2), the latter
have to be redirected to the object allocator. */
#define PyMem_Del PyObject_Free
/* Macros */
#define PyMem_NEW(type, n) \
( (type *) PyMem_MALLOC((n) * sizeof(type)) )
#define PyMem_Resize(p, type, n) \
( (p) = (type *) PyMem_Realloc((p), (n) * sizeof(type)) )
#define PyMem_RESIZE(p, type, n) \
( (p) = (type *) PyMem_REALLOC((p), (n) * sizeof(type)) )
/* In order to avoid breaking old code mixing PyObject_{New, NEW} with
PyMem_{Del, DEL} and PyMem_{Free, FREE}, the PyMem "release memory"
functions have to be redirected to the object deallocator. */
#define PyMem_Del PyObject_Free
#define PyMem_DEL PyObject_FREE
#ifdef __cplusplus
......
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