Include/objimpl.h

   1 /* The PyObject_ memory family:  high-level object memory interfaces.
   2    See pymem.h for the low-level PyMem_ family.
   3 */
   4
   5 #ifndef Py_OBJIMPL_H
   6 #define Py_OBJIMPL_H
   7
   8 #include "pymem.h"
   9
  10 #ifdef __cplusplus
  11 extern "C" {
  12 #endif
  13
  14 /* BEWARE:
  15
  16    Each interface exports both functions and macros.  Extension modules should
  17    use the functions, to ensure binary compatibility across Python versions.
  18    Because the Python implementation is free to change internal details, and
  19    the macros may (or may not) expose details for speed, if you do use the
  20    macros you must recompile your extensions with each Python release.
  21
  22    Never mix calls to PyObject_ memory functions with calls to the platform
  23    malloc/realloc/ calloc/free, or with calls to PyMem_.
  24 */
  25
  26 /*
  27 Functions and macros for modules that implement new object types.
  28
  29  - PyObject_New(type, typeobj) allocates memory for a new object of the given
  30    type, and initializes part of it.  'type' must be the C structure type used
  31    to represent the object, and 'typeobj' the address of the corresponding
  32    type object.  Reference count and type pointer are filled in; the rest of
  33    the bytes of the object are *undefined*!  The resulting expression type is
  34    'type *'.  The size of the object is determined by the tp_basicsize field
  35    of the type object.
  36
  37  - PyObject_NewVar(type, typeobj, n) is similar but allocates a variable-size
  38    object with room for n items.  In addition to the refcount and type pointer
  39    fields, this also fills in the ob_size field.
  40
  41  - PyObject_Del(op) releases the memory allocated for an object.  It does not
  42    run a destructor -- it only frees the memory.  PyObject_Free is identical.
  43
  44  - PyObject_Init(op, typeobj) and PyObject_InitVar(op, typeobj, n) don't
  45    allocate memory.  Instead of a 'type' parameter, they take a pointer to a
  46    new object (allocated by an arbitrary allocator), and initialize its object
  47    header fields.
  48
  49 Note that objects created with PyObject_{New, NewVar} are allocated using the
  50 specialized Python allocator (implemented in obmalloc.c), if WITH_PYMALLOC is
  51 enabled.  In addition, a special debugging allocator is used if PYMALLOC_DEBUG
  52 is also #defined.
  53
  54 In case a specific form of memory management is needed (for example, if you
  55 must use the platform malloc heap(s), or shared memory, or C++ local storage or
  56 operator new), you must first allocate the object with your custom allocator,
  57 then pass its pointer to PyObject_{Init, InitVar} for filling in its Python-
  58 specific fields:  reference count, type pointer, possibly others.  You should
  59 be aware that Python no control over these objects because they don't
  60 cooperate with the Python memory manager.  Such objects may not be eligible
  61 for automatic garbage collection and you have to make sure that they are
  62 released accordingly whenever their destructor gets called (cf. the specific
  63 form of memory management you're using).
  64
  65 Unless you have specific memory management requirements, use
  66 PyObject_{New, NewVar, Del}.
  67 */
  68
  69 /*
  70  * Raw object memory interface
  71  * ===========================
  72  */
  73
  74 /* Functions to call the same malloc/realloc/free as used by Python's
  75    object allocator.  If WITH_PYMALLOC is enabled, these may differ from
  76    the platform malloc/realloc/free.  The Python object allocator is
  77    designed for fast, cache-conscious allocation of many "small" objects,
  78    and with low hidden memory overhead.
  79
  80    PyObject_Malloc(0) returns a unique non-NULL pointer if possible.
  81
  82    PyObject_Realloc(NULL, n) acts like PyObject_Malloc(n).
  83    PyObject_Realloc(p != NULL, 0) does not return  NULL, or free the memory
  84    at p.
  85
  86    Returned pointers must be checked for NULL explicitly; no action is
  87    performed on failure other than to return NULL (no warning it printed, no
  88    exception is set, etc).
  89
  90    For allocating objects, use PyObject_{New, NewVar} instead whenever
  91    possible.  The PyObject_{Malloc, Realloc, Free} family is exposed
  92    so that you can exploit Python's small-block allocator for non-object
  93    uses.  If you must use these routines to allocate object memory, make sure
  94    the object gets initialized via PyObject_{Init, InitVar} after obtaining
  95    the raw memory.
  96 */
  97 PyAPI_FUNC(void *) PyObject_Malloc(size_t);
  98 PyAPI_FUNC(void *) PyObject_Realloc(void *, size_t);
  99 PyAPI_FUNC(void) PyObject_Free(void *);
 100
 101
 102 /* Macros */
 103 #ifdef WITH_PYMALLOC
 104 #ifdef PYMALLOC_DEBUG
 105 PyAPI_FUNC(void *) _PyObject_DebugMalloc(size_t nbytes);
 106 PyAPI_FUNC(void *) _PyObject_DebugRealloc(void *p, size_t nbytes);
 107 PyAPI_FUNC(void) _PyObject_DebugFree(void *p);
 108 PyAPI_FUNC(void) _PyObject_DebugDumpAddress(const void *p);
 109 PyAPI_FUNC(void) _PyObject_DebugCheckAddress(const void *p);
 110 PyAPI_FUNC(void) _PyObject_DebugMallocStats(void);
 111 #define PyObject_MALLOC         _PyObject_DebugMalloc
 112 #define PyObject_Malloc         _PyObject_DebugMalloc
 113 #define PyObject_REALLOC        _PyObject_DebugRealloc
 114 #define PyObject_Realloc        _PyObject_DebugRealloc
 115 #define PyObject_FREE           _PyObject_DebugFree
 116 #define PyObject_Free           _PyObject_DebugFree
 117
 118 #else   /* WITH_PYMALLOC && ! PYMALLOC_DEBUG */
 119 #define PyObject_MALLOC         PyObject_Malloc
 120 #define PyObject_REALLOC        PyObject_Realloc
 121 #define PyObject_FREE           PyObject_Free
 122 #endif
 123
 124 #else   /* ! WITH_PYMALLOC */
 125 #define PyObject_MALLOC         PyMem_MALLOC
 126 #define PyObject_REALLOC        PyMem_REALLOC
 127 /* This is an odd one!  For backward compatibility with old extensions, the
 128    PyMem "release memory" functions have to invoke the object allocator's
 129    free() function.  When pymalloc isn't enabled, that leaves us using
 130    the platform free(). */
 131 #define PyObject_FREE           free
 132
 133 #endif  /* WITH_PYMALLOC */
 134
 135 #define PyObject_Del            PyObject_Free
 136 #define PyObject_DEL            PyObject_FREE
 137
 138 /* for source compatibility with 2.2 */
 139 #define _PyObject_Del           PyObject_Free
 140
 141 /*
 142  * Generic object allocator interface
 143  * ==================================
 144  */
 145
 146 /* Functions */
 147 PyAPI_FUNC(PyObject *) PyObject_Init(PyObject *, PyTypeObject *);
 148 PyAPI_FUNC(PyVarObject *) PyObject_InitVar(PyVarObject *,
 149                                                  PyTypeObject *, int);
 150 PyAPI_FUNC(PyObject *) _PyObject_New(PyTypeObject *);
 151 PyAPI_FUNC(PyVarObject *) _PyObject_NewVar(PyTypeObject *, int);
 152
 153 #define PyObject_New(type, typeobj) \
 154                 ( (type *) _PyObject_New(typeobj) )
 155 #define PyObject_NewVar(type, typeobj, n) \
 156                 ( (type *) _PyObject_NewVar((typeobj), (n)) )
 157
 158 /* Macros trading binary compatibility for speed. See also pymem.h.
 159    Note that these macros expect non-NULL object pointers.*/
 160 #define PyObject_INIT(op, typeobj) \
 161         ( (op)->ob_type = (typeobj), _Py_NewReference((PyObject *)(op)), (op) )
 162 #define PyObject_INIT_VAR(op, typeobj, size) \
 163         ( (op)->ob_size = (size), PyObject_INIT((op), (typeobj)) )
 164
 165 #define _PyObject_SIZE(typeobj) ( (typeobj)->tp_basicsize )
 166
 167 /* _PyObject_VAR_SIZE returns the number of bytes (as size_t) allocated for a
 168    vrbl-size object with nitems items, exclusive of gc overhead (if any).  The
 169    value is rounded up to the closest multiple of sizeof(void *), in order to
 170    ensure that pointer fields at the end of the object are correctly aligned
 171    for the platform (this is of special importance for subclasses of, e.g.,
 172    str or long, so that pointers can be stored after the embedded data).
 173
 174    Note that there's no memory wastage in doing this, as malloc has to
 175    return (at worst) pointer-aligned memory anyway.
 176 */
 177 #if ((SIZEOF_VOID_P - 1) & SIZEOF_VOID_P) != 0
 178 #   error "_PyObject_VAR_SIZE requires SIZEOF_VOID_P be a power of 2"
 179 #endif
 180
 181 #define _PyObject_VAR_SIZE(typeobj, nitems)     \
 182         (size_t)                                \
 183         ( ( (typeobj)->tp_basicsize +           \
 184             (nitems)*(typeobj)->tp_itemsize +   \
 185             (SIZEOF_VOID_P - 1)                 \
 186           ) & ~(SIZEOF_VOID_P - 1)              \
 187         )
 188
 189 #define PyObject_NEW(type, typeobj) \
 190 ( (type *) PyObject_Init( \
 191         (PyObject *) PyObject_MALLOC( _PyObject_SIZE(typeobj) ), (typeobj)) )
 192
 193 #define PyObject_NEW_VAR(type, typeobj, n) \
 194 ( (type *) PyObject_InitVar( \
 195       (PyVarObject *) PyObject_MALLOC(_PyObject_VAR_SIZE((typeobj),(n)) ),\
 196       (typeobj), (n)) )
 197
 198 /* This example code implements an object constructor with a custom
 199    allocator, where PyObject_New is inlined, and shows the important
 200    distinction between two steps (at least):
 201        1) the actual allocation of the object storage;
 202        2) the initialization of the Python specific fields
 203           in this storage with PyObject_{Init, InitVar}.
 204
 205    PyObject *
 206    YourObject_New(...)
 207    {
 208        PyObject *op;
 209
 210        op = (PyObject *) Your_Allocator(_PyObject_SIZE(YourTypeStruct));
 211        if (op == NULL)
 212            return PyErr_NoMemory();
 213
 214        PyObject_Init(op, &YourTypeStruct);
 215
 216        op->ob_field = value;
 217        ...
 218        return op;
 219    }
 220
 221    Note that in C++, the use of the new operator usually implies that
 222    the 1st step is performed automatically for you, so in a C++ class
 223    constructor you would start directly with PyObject_Init/InitVar
 224 */
 225
 226 /*
 227  * Garbage Collection Support
 228  * ==========================
 229  */
 230
 231 /* C equivalent of gc.collect(). */
 232 long PyGC_Collect(void);
 233
 234 /* Test if a type has a GC head */
 235 #define PyType_IS_GC(t) PyType_HasFeature((t), Py_TPFLAGS_HAVE_GC)
 236
 237 /* Test if an object has a GC head */
 238 #define PyObject_IS_GC(o) (PyType_IS_GC((o)->ob_type) && \
 239         ((o)->ob_type->tp_is_gc == NULL || (o)->ob_type->tp_is_gc(o)))
 240
 241 PyAPI_FUNC(PyVarObject *) _PyObject_GC_Resize(PyVarObject *, int);
 242 #define PyObject_GC_Resize(type, op, n) \
 243                 ( (type *) _PyObject_GC_Resize((PyVarObject *)(op), (n)) )
 244
 245 /* for source compatibility with 2.2 */
 246 #define _PyObject_GC_Del PyObject_GC_Del
 247
 248 /* GC information is stored BEFORE the object structure. */
 249 typedef union _gc_head {
 250         struct {
 251                 union _gc_head *gc_next;
 252                 union _gc_head *gc_prev;
 253                 int gc_refs;
 254         } gc;
 255         long double dummy;  /* force worst-case alignment */
 256 } PyGC_Head;
 257
 258 extern PyGC_Head *_PyGC_generation0;
 259
 260 #define _Py_AS_GC(o) ((PyGC_Head *)(o)-1)
 261
 262 #define _PyGC_REFS_UNTRACKED                    (-2)
 263 #define _PyGC_REFS_REACHABLE                    (-3)
 264 #define _PyGC_REFS_TENTATIVELY_UNREACHABLE      (-4)
 265
 266 /* Tell the GC to track this object.  NB: While the object is tracked the
 267  * collector it must be safe to call the ob_traverse method. */
 268 #define _PyObject_GC_TRACK(o) do { \
 269         PyGC_Head *g = _Py_AS_GC(o); \
 270         if (g->gc.gc_refs != _PyGC_REFS_UNTRACKED) \
 271                 Py_FatalError("GC object already tracked"); \
 272         g->gc.gc_refs = _PyGC_REFS_REACHABLE; \
 273         g->gc.gc_next = _PyGC_generation0; \
 274         g->gc.gc_prev = _PyGC_generation0->gc.gc_prev; \
 275         g->gc.gc_prev->gc.gc_next = g; \
 276         _PyGC_generation0->gc.gc_prev = g; \
 277     } while (0);
 278
 279 /* Tell the GC to stop tracking this object.
 280  * gc_next doesn't need to be set to NULL, but doing so is a good
 281  * way to provoke memory errors if calling code is confused.
 282  */
 283 #define _PyObject_GC_UNTRACK(o) do { \
 284         PyGC_Head *g = _Py_AS_GC(o); \
 285         assert(g->gc.gc_refs != _PyGC_REFS_UNTRACKED); \
 286         g->gc.gc_refs = _PyGC_REFS_UNTRACKED; \
 287         g->gc.gc_prev->gc.gc_next = g->gc.gc_next; \
 288         g->gc.gc_next->gc.gc_prev = g->gc.gc_prev; \
 289         g->gc.gc_next = NULL; \
 290     } while (0);
 291
 292 PyAPI_FUNC(PyObject *) _PyObject_GC_Malloc(size_t);
 293 PyAPI_FUNC(PyObject *) _PyObject_GC_New(PyTypeObject *);
 294 PyAPI_FUNC(PyVarObject *) _PyObject_GC_NewVar(PyTypeObject *, int);
 295 PyAPI_FUNC(void) PyObject_GC_Track(void *);
 296 PyAPI_FUNC(void) PyObject_GC_UnTrack(void *);
 297 PyAPI_FUNC(void) PyObject_GC_Del(void *);
 298
 299 #define PyObject_GC_New(type, typeobj) \
 300                 ( (type *) _PyObject_GC_New(typeobj) )
 301 #define PyObject_GC_NewVar(type, typeobj, n) \
 302                 ( (type *) _PyObject_GC_NewVar((typeobj), (n)) )
 303
 304
 305 /* Utility macro to help write tp_traverse functions.
 306  * To use this macro, the tp_traverse function must name its arguments
 307  * "visit" and "arg".  This is intended to keep tp_traverse functions
 308  * looking as much alike as possible.
 309  */
 310 #define Py_VISIT(op)                                    \
 311         do {                                            \
 312                 if (op) {                               \
 313                         int vret = visit((op), arg);    \
 314                         if (vret)                       \
 315                                 return vret;            \
 316                 }                                       \
 317         } while (0)
 318
 319 /* This is here for the sake of backwards compatibility.  Extensions that
 320  * use the old GC API will still compile but the objects will not be
 321  * tracked by the GC. */
 322 #define PyGC_HEAD_SIZE 0
 323 #define PyObject_GC_Init(op)
 324 #define PyObject_GC_Fini(op)
 325 #define PyObject_AS_GC(op) (op)
 326 #define PyObject_FROM_GC(op) (op)
 327
 328
 329 /* Test if a type supports weak references */
 330 #define PyType_SUPPORTS_WEAKREFS(t) \
 331         (PyType_HasFeature((t), Py_TPFLAGS_HAVE_WEAKREFS) \
 332          && ((t)->tp_weaklistoffset > 0))
 333
 334 #define PyObject_GET_WEAKREFS_LISTPTR(o) \
 335         ((PyObject **) (((char *) (o)) + (o)->ob_type->tp_weaklistoffset))
 336
 337 #ifdef __cplusplus
 338 }
 339 #endif
 340 #endif /* !Py_OBJIMPL_H */