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