Moving pymalloc along.

tim-one · tim-one · commit 8b078f95e0a9 · 2002-04-28T04:11:46.000Z
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.
diff --git a/Include/objimpl.h b/Include/objimpl.h
@@ -1,3 +1,6 @@
+/* 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 *);
@@ -114,14 +124,19 @@ 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
-#define PyObject_DEL PyObject_FREE
+#define PyObject_Del		PyObject_Free
+#define PyObject_DEL		PyObject_FREE
 
 /* for source compatibility with 2.2 */
-#define _PyObject_Del PyObject_Free
+#define _PyObject_Del		PyObject_Free
 
 /*
  * Generic object allocator interface
@@ -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 */
@@ -283,10 +297,10 @@ extern DL_IMPORT(void) PyObject_GC_Del(void *);
 
 #else /* !WITH_CYCLE_GC */
 
-#define _PyObject_GC_Malloc PyObject_Malloc
-#define PyObject_GC_New PyObject_New
-#define PyObject_GC_NewVar PyObject_NewVar
-#define PyObject_GC_Del	 PyObject_Del
+#define _PyObject_GC_Malloc	PyObject_Malloc
+#define PyObject_GC_New		PyObject_New
+#define PyObject_GC_NewVar	PyObject_NewVar
+#define PyObject_GC_Del		PyObject_Del
 #define _PyObject_GC_TRACK(op)
 #define _PyObject_GC_UNTRACK(op)
 #define PyObject_GC_Track(op)
diff --git a/Include/pymem.h b/Include/pymem.h
@@ -1,5 +1,6 @@
-
-/* 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 */
 
@@ -65,41 +67,44 @@ 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)) )
 
-#define PyMem_DEL PyObject_FREE
+/* 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
 }
