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   /* WITH_PYMALLOC && 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 PyAPI_FUNC(void *) _PyObject_DebugMallocApi(char api, size_t nbytes);
 112 PyAPI_FUNC(void *) _PyObject_DebugReallocApi(char api, void *p, size_t nbytes);
 113 PyAPI_FUNC(void) _PyObject_DebugFreeApi(char api, void *p);
 114 PyAPI_FUNC(void) _PyObject_DebugCheckAddressApi(char api, const void *p);
 115 PyAPI_FUNC(void *) _PyMem_DebugMalloc(size_t nbytes);
 116 PyAPI_FUNC(void *) _PyMem_DebugRealloc(void *p, size_t nbytes);
 117 PyAPI_FUNC(void) _PyMem_DebugFree(void *p);
 118 #define PyObject_MALLOC         _PyObject_DebugMalloc
 119 #define PyObject_Malloc         _PyObject_DebugMalloc
 120 #define PyObject_REALLOC        _PyObject_DebugRealloc
 121 #define PyObject_Realloc        _PyObject_DebugRealloc
 122 #define PyObject_FREE           _PyObject_DebugFree
 123 #define PyObject_Free           _PyObject_DebugFree
 124
 125 #else   /* WITH_PYMALLOC && ! PYMALLOC_DEBUG */
 126 #define PyObject_MALLOC         PyObject_Malloc
 127 #define PyObject_REALLOC        PyObject_Realloc
 128 #define PyObject_FREE           PyObject_Free
 129 #endif
 130
 131 #else   /* ! WITH_PYMALLOC */
 132 #define PyObject_MALLOC         PyMem_MALLOC
 133 #define PyObject_REALLOC        PyMem_REALLOC
 134 #define PyObject_FREE           PyMem_FREE
 135
 136 #endif  /* WITH_PYMALLOC */
 137
 138 #define PyObject_Del            PyObject_Free
 139 #define PyObject_DEL            PyObject_FREE
 140
 141 /* for source compatibility with 2.2 */
 142 #define _PyObject_Del           PyObject_Free
 143
 144 /*
 145  * Generic object allocator interface
 146  * ==================================
 147  */
 148
 149 /* Functions */
 150 PyAPI_FUNC(PyObject *) PyObject_Init(PyObject *, PyTypeObject *);
 151 PyAPI_FUNC(PyVarObject *) PyObject_InitVar(PyVarObject *,
 152                                                  PyTypeObject *, Py_ssize_t);
 153 PyAPI_FUNC(PyObject *) _PyObject_New(PyTypeObject *);
 154 PyAPI_FUNC(PyVarObject *) _PyObject_NewVar(PyTypeObject *, Py_ssize_t);
 155
 156 #define PyObject_New(type, typeobj) \
 157                 ( (type *) _PyObject_New(typeobj) )
 158 #define PyObject_NewVar(type, typeobj, n) \
 159                 ( (type *) _PyObject_NewVar((typeobj), (n)) )
 160
 161 /* Macros trading binary compatibility for speed. See also pymem.h.
 162    Note that these macros expect non-NULL object pointers.*/
 163 #define PyObject_INIT(op, typeobj) \
 164         ( Py_TYPE(op) = (typeobj), _Py_NewReference((PyObject *)(op)), (op) )
 165 #define PyObject_INIT_VAR(op, typeobj, size) \
 166         ( Py_SIZE(op) = (size), PyObject_INIT((op), (typeobj)) )
 167
 168 #define _PyObject_SIZE(typeobj) ( (typeobj)->tp_basicsize )
 169
 170 /* _PyObject_VAR_SIZE returns the number of bytes (as size_t) allocated for a
 171    vrbl-size object with nitems items, exclusive of gc overhead (if any).  The
 172    value is rounded up to the closest multiple of sizeof(void *), in order to
 173    ensure that pointer fields at the end of the object are correctly aligned
 174    for the platform (this is of special importance for subclasses of, e.g.,
 175    str or long, so that pointers can be stored after the embedded data).
 176
 177    Note that there's no memory wastage in doing this, as malloc has to
 178    return (at worst) pointer-aligned memory anyway.
 179 */
 180 #if ((SIZEOF_VOID_P - 1) & SIZEOF_VOID_P) != 0
 181 #   error "_PyObject_VAR_SIZE requires SIZEOF_VOID_P be a power of 2"
 182 #endif
 183
 184 #define _PyObject_VAR_SIZE(typeobj, nitems)     \
 185         (size_t)                                \
 186         ( ( (typeobj)->tp_basicsize +           \
 187             (nitems)*(typeobj)->tp_itemsize +   \
 188             (SIZEOF_VOID_P - 1)                 \
 189           ) & ~(SIZEOF_VOID_P - 1)              \
 190         )
 191
 192 #define PyObject_NEW(type, typeobj) \
 193 ( (type *) PyObject_Init( \
 194         (PyObject *) PyObject_MALLOC( _PyObject_SIZE(typeobj) ), (typeobj)) )
 195
 196 #define PyObject_NEW_VAR(type, typeobj, n) \
 197 ( (type *) PyObject_InitVar( \
 198       (PyVarObject *) PyObject_MALLOC(_PyObject_VAR_SIZE((typeobj),(n)) ),\
 199       (typeobj), (n)) )
 200
 201 /* This example code implements an object constructor with a custom
 202    allocator, where PyObject_New is inlined, and shows the important
 203    distinction between two steps (at least):
 204        1) the actual allocation of the object storage;
 205        2) the initialization of the Python specific fields
 206           in this storage with PyObject_{Init, InitVar}.
 207
 208    PyObject *
 209    YourObject_New(...)
 210    {
 211        PyObject *op;
 212
 213        op = (PyObject *) Your_Allocator(_PyObject_SIZE(YourTypeStruct));
 214        if (op == NULL)
 215            return PyErr_NoMemory();
 216
 217        PyObject_Init(op, &YourTypeStruct);
 218
 219        op->ob_field = value;
 220        ...
 221        return op;
 222    }
 223
 224    Note that in C++, the use of the new operator usually implies that
 225    the 1st step is performed automatically for you, so in a C++ class
 226    constructor you would start directly with PyObject_Init/InitVar
 227 */
 228
 229 /*
 230  * Garbage Collection Support
 231  * ==========================
 232  */
 233
 234 /* C equivalent of gc.collect(). */
 235 PyAPI_FUNC(Py_ssize_t) PyGC_Collect(void);
 236
 237 /* Test if a type has a GC head */
 238 #define PyType_IS_GC(t) PyType_HasFeature((t), Py_TPFLAGS_HAVE_GC)
 239
 240 /* Test if an object has a GC head */
 241 #define PyObject_IS_GC(o) (PyType_IS_GC(Py_TYPE(o)) && \
 242         (Py_TYPE(o)->tp_is_gc == NULL || Py_TYPE(o)->tp_is_gc(o)))
 243
 244 PyAPI_FUNC(PyVarObject *) _PyObject_GC_Resize(PyVarObject *, Py_ssize_t);
 245 #define PyObject_GC_Resize(type, op, n) \
 246                 ( (type *) _PyObject_GC_Resize((PyVarObject *)(op), (n)) )
 247
 248 /* for source compatibility with 2.2 */
 249 #define _PyObject_GC_Del PyObject_GC_Del
 250
 251 /* GC information is stored BEFORE the object structure. */
 252 typedef union _gc_head {
 253         struct {
 254                 union _gc_head *gc_next;
 255                 union _gc_head *gc_prev;
 256                 Py_ssize_t gc_refs;
 257         } gc;
 258         long double dummy;  /* force worst-case alignment */
 259 } PyGC_Head;
 260
 261 extern PyGC_Head *_PyGC_generation0;
 262
 263 #define _Py_AS_GC(o) ((PyGC_Head *)(o)-1)
 264
 265 #define _PyGC_REFS_UNTRACKED                    (-2)
 266 #define _PyGC_REFS_REACHABLE                    (-3)
 267 #define _PyGC_REFS_TENTATIVELY_UNREACHABLE      (-4)
 268
 269 /* Tell the GC to track this object.  NB: While the object is tracked the
 270  * collector it must be safe to call the ob_traverse method. */
 271 #define _PyObject_GC_TRACK(o) do { \
 272         PyGC_Head *g = _Py_AS_GC(o); \
 273         if (g->gc.gc_refs != _PyGC_REFS_UNTRACKED) \
 274                 Py_FatalError("GC object already tracked"); \
 275         g->gc.gc_refs = _PyGC_REFS_REACHABLE; \
 276         g->gc.gc_next = _PyGC_generation0; \
 277         g->gc.gc_prev = _PyGC_generation0->gc.gc_prev; \
 278         g->gc.gc_prev->gc.gc_next = g; \
 279         _PyGC_generation0->gc.gc_prev = g; \
 280     } while (0);
 281
 282 /* Tell the GC to stop tracking this object.
 283  * gc_next doesn't need to be set to NULL, but doing so is a good
 284  * way to provoke memory errors if calling code is confused.
 285  */
 286 #define _PyObject_GC_UNTRACK(o) do { \
 287         PyGC_Head *g = _Py_AS_GC(o); \
 288         assert(g->gc.gc_refs != _PyGC_REFS_UNTRACKED); \
 289         g->gc.gc_refs = _PyGC_REFS_UNTRACKED; \
 290         g->gc.gc_prev->gc.gc_next = g->gc.gc_next; \
 291         g->gc.gc_next->gc.gc_prev = g->gc.gc_prev; \
 292         g->gc.gc_next = NULL; \
 293     } while (0);
 294
 295 /* True if the object is currently tracked by the GC. */
 296 #define _PyObject_GC_IS_TRACKED(o) \
 297         ((_Py_AS_GC(o))->gc.gc_refs != _PyGC_REFS_UNTRACKED)
 298
 299 /* True if the object may be tracked by the GC in the future, or already is.
 300    This can be useful to implement some optimizations. */
 301 #define _PyObject_GC_MAY_BE_TRACKED(obj) \
 302         (PyObject_IS_GC(obj) && \
 303                 (!PyTuple_CheckExact(obj) || _PyObject_GC_IS_TRACKED(obj)))
 304
 305
 306 PyAPI_FUNC(PyObject *) _PyObject_GC_Malloc(size_t);
 307 PyAPI_FUNC(PyObject *) _PyObject_GC_New(PyTypeObject *);
 308 PyAPI_FUNC(PyVarObject *) _PyObject_GC_NewVar(PyTypeObject *, Py_ssize_t);
 309 PyAPI_FUNC(void) PyObject_GC_Track(void *);
 310 PyAPI_FUNC(void) PyObject_GC_UnTrack(void *);
 311 PyAPI_FUNC(void) PyObject_GC_Del(void *);
 312
 313 #define PyObject_GC_New(type, typeobj) \
 314                 ( (type *) _PyObject_GC_New(typeobj) )
 315 #define PyObject_GC_NewVar(type, typeobj, n) \
 316                 ( (type *) _PyObject_GC_NewVar((typeobj), (n)) )
 317
 318
 319 /* Utility macro to help write tp_traverse functions.
 320  * To use this macro, the tp_traverse function must name its arguments
 321  * "visit" and "arg".  This is intended to keep tp_traverse functions
 322  * looking as much alike as possible.
 323  */
 324 #define Py_VISIT(op)                                                    \
 325         do {                                                            \
 326                 if (op) {                                               \
 327                         int vret = visit((PyObject *)(op), arg);        \
 328                         if (vret)                                       \
 329                                 return vret;                            \
 330                 }                                                       \
 331         } while (0)
 332
 333 /* This is here for the sake of backwards compatibility.  Extensions that
 334  * use the old GC API will still compile but the objects will not be
 335  * tracked by the GC. */
 336 #define PyGC_HEAD_SIZE 0
 337 #define PyObject_GC_Init(op)
 338 #define PyObject_GC_Fini(op)
 339 #define PyObject_AS_GC(op) (op)
 340 #define PyObject_FROM_GC(op) (op)
 341
 342
 343 /* Test if a type supports weak references */
 344 #define PyType_SUPPORTS_WEAKREFS(t) \
 345         (PyType_HasFeature((t), Py_TPFLAGS_HAVE_WEAKREFS) \
 346          && ((t)->tp_weaklistoffset > 0))
 347
 348 #define PyObject_GET_WEAKREFS_LISTPTR(o) \
 349         ((PyObject **) (((char *) (o)) + Py_TYPE(o)->tp_weaklistoffset))
 350
 351 #ifdef __cplusplus
 352 }
 353 #endif
 354 #endif /* !Py_OBJIMPL_H */