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