Include/objimpl.h

   1
   2 #ifndef Py_OBJIMPL_H
   3 #define Py_OBJIMPL_H
   4
   5 #include "pymem.h"
   6
   7 #ifdef __cplusplus
   8 extern "C" {
   9 #endif
  10
  11 /*
  12 Functions and macros for modules that implement new object types.
  13 You must first include "object.h".
  14
  15  - PyObject_New(type, typeobj) allocates memory for a new object of
  16    the given type; here 'type' must be the C structure type used to
  17    represent the object and 'typeobj' the address of the corresponding
  18    type object.  Reference count and type pointer are filled in; the
  19    rest of the bytes of the object are *undefined*!  The resulting
  20    expression type is 'type *'.  The size of the object is actually
  21    determined by the tp_basicsize field of the type object.
  22
  23  - PyObject_NewVar(type, typeobj, n) is similar but allocates a
  24    variable-size object with n extra items.  The size is computed as
  25    tp_basicsize plus n * tp_itemsize.  This fills in the ob_size field
  26    as well.
  27
  28  - PyObject_Del(op) releases the memory allocated for an object.
  29
  30  - PyObject_Init(op, typeobj) and PyObject_InitVar(op, typeobj, n) are
  31    similar to PyObject_{New, NewVar} except that they don't allocate
  32    the memory needed for an object. Instead of the 'type' parameter,
  33    they accept the pointer of a new object (allocated by an arbitrary
  34    allocator) and initialize its object header fields.
  35
  36 Note that objects created with PyObject_{New, NewVar} are allocated
  37 within the Python heap by an object allocator, the latter being
  38 implemented (by default) on top of the Python raw memory
  39 allocator. This ensures that Python keeps control on the user's
  40 objects regarding their memory management; for instance, they may be
  41 subject to automatic garbage collection.
  42
  43 In case a specific form of memory management is needed, implying that
  44 the objects would not reside in the Python heap (for example standard
  45 malloc heap(s) are mandatory, use of shared memory, C++ local storage
  46 or operator new), you must first allocate the object with your custom
  47 allocator, then pass its pointer to PyObject_{Init, InitVar} for
  48 filling in its Python-specific fields: reference count, type pointer,
  49 possibly others. You should be aware that Python has very limited
  50 control over these objects because they don't cooperate with the
  51 Python memory manager. Such objects may not be eligible for automatic
  52 garbage collection and you have to make sure that they are released
  53 accordingly whenever their destructor gets called (cf. the specific
  54 form of memory management you're using).
  55
  56 Unless you have specific memory management requirements, it is
  57 recommended to use PyObject_{New, NewVar, Del}. */
  58
  59 /*
  60  * Core object memory allocator
  61  * ============================
  62  */
  63
  64 /* The purpose of the object allocator is to make the distinction
  65    between "object memory" and the rest within the Python heap.
  66
  67    Object memory is the one allocated by PyObject_{New, NewVar}, i.e.
  68    the one that holds the object's representation defined by its C
  69    type structure, *excluding* any object-specific memory buffers that
  70    might be referenced by the structure (for type structures that have
  71    pointer fields).  By default, the object memory allocator is
  72    implemented on top of the raw memory allocator.
  73
  74    The PyCore_* macros can be defined to make the interpreter use a
  75    custom object memory allocator. They are reserved for internal
  76    memory management purposes exclusively. Both the core and extension
  77    modules should use the PyObject_* API. */
  78
  79 #ifndef PyCore_OBJECT_MALLOC_FUNC
  80 #undef PyCore_OBJECT_REALLOC_FUNC
  81 #undef PyCore_OBJECT_FREE_FUNC
  82 #define PyCore_OBJECT_MALLOC_FUNC    PyCore_MALLOC_FUNC
  83 #define PyCore_OBJECT_REALLOC_FUNC   PyCore_REALLOC_FUNC
  84 #define PyCore_OBJECT_FREE_FUNC      PyCore_FREE_FUNC
  85 #endif
  86
  87 #ifndef PyCore_OBJECT_MALLOC_PROTO
  88 #undef PyCore_OBJECT_REALLOC_PROTO
  89 #undef PyCore_OBJECT_FREE_PROTO
  90 #define PyCore_OBJECT_MALLOC_PROTO   PyCore_MALLOC_PROTO
  91 #define PyCore_OBJECT_REALLOC_PROTO  PyCore_REALLOC_PROTO
  92 #define PyCore_OBJECT_FREE_PROTO     PyCore_FREE_PROTO
  93 #endif
  94
  95 #ifdef NEED_TO_DECLARE_OBJECT_MALLOC_AND_FRIEND
  96 extern void *PyCore_OBJECT_MALLOC_FUNC PyCore_OBJECT_MALLOC_PROTO;
  97 extern void *PyCore_OBJECT_REALLOC_FUNC PyCore_OBJECT_REALLOC_PROTO;
  98 extern void PyCore_OBJECT_FREE_FUNC PyCore_OBJECT_FREE_PROTO;
  99 #endif
 100
 101 #ifndef PyCore_OBJECT_MALLOC
 102 #undef PyCore_OBJECT_REALLOC
 103 #undef PyCore_OBJECT_FREE
 104 #define PyCore_OBJECT_MALLOC(n)      PyCore_OBJECT_MALLOC_FUNC(n)
 105 #define PyCore_OBJECT_REALLOC(p, n)  PyCore_OBJECT_REALLOC_FUNC((p), (n))
 106 #define PyCore_OBJECT_FREE(p)        PyCore_OBJECT_FREE_FUNC(p)
 107 #endif
 108
 109 /*
 110  * Raw object memory interface
 111  * ===========================
 112  */
 113
 114 /* The use of this API should be avoided, unless a builtin object
 115    constructor inlines PyObject_{New, NewVar}, either because the
 116    latter functions cannot allocate the exact amount of needed memory,
 117    either for speed. This situation is exceptional, but occurs for
 118    some object constructors (PyBuffer_New, PyList_New...).  Inlining
 119    PyObject_{New, NewVar} for objects that are supposed to belong to
 120    the Python heap is discouraged. If you really have to, make sure
 121    the object is initialized with PyObject_{Init, InitVar}. Do *not*
 122    inline PyObject_{Init, InitVar} for user-extension types or you
 123    might seriously interfere with Python's memory management. */
 124
 125 /* Functions */
 126
 127 /* Wrappers around PyCore_OBJECT_MALLOC and friends; useful if you
 128    need to be sure that you are using the same object memory allocator
 129    as Python. These wrappers *do not* make sure that allocating 0
 130    bytes returns a non-NULL pointer. Returned pointers must be checked
 131    for NULL explicitly; no action is performed on failure. */
 132 extern DL_IMPORT(void *) PyObject_Malloc(size_t);
 133 extern DL_IMPORT(void *) PyObject_Realloc(void *, size_t);
 134 extern DL_IMPORT(void) PyObject_Free(void *);
 135
 136 /* Macros */
 137 #define PyObject_MALLOC(n)           PyCore_OBJECT_MALLOC(n)
 138 #define PyObject_REALLOC(op, n)      PyCore_OBJECT_REALLOC((void *)(op), (n))
 139 #define PyObject_FREE(op)            PyCore_OBJECT_FREE((void *)(op))
 140
 141 /*
 142  * Generic object allocator interface
 143  * ==================================
 144  */
 145
 146 /* Functions */
 147 extern DL_IMPORT(PyObject *) PyObject_Init(PyObject *, PyTypeObject *);
 148 extern DL_IMPORT(PyVarObject *) PyObject_InitVar(PyVarObject *,
 149                                                  PyTypeObject *, int);
 150 extern DL_IMPORT(PyObject *) _PyObject_New(PyTypeObject *);
 151 extern DL_IMPORT(PyVarObject *) _PyObject_NewVar(PyTypeObject *, int);
 152 extern DL_IMPORT(void) _PyObject_Del(PyObject *);
 153
 154 #define PyObject_New(type, typeobj) \
 155                 ( (type *) _PyObject_New(typeobj) )
 156 #define PyObject_NewVar(type, typeobj, n) \
 157                 ( (type *) _PyObject_NewVar((typeobj), (n)) )
 158 #define PyObject_Del(op) _PyObject_Del((PyObject *)(op))
 159
 160 /* Macros trading binary compatibility for speed. See also pymem.h.
 161    Note that these macros expect non-NULL object pointers.*/
 162 #define PyObject_INIT(op, typeobj) \
 163         ( (op)->ob_type = (typeobj), _Py_NewReference((PyObject *)(op)), (op) )
 164 #define PyObject_INIT_VAR(op, typeobj, size) \
 165         ( (op)->ob_size = (size), PyObject_INIT((op), (typeobj)) )
 166
 167 #define _PyObject_SIZE(typeobj) ( (typeobj)->tp_basicsize )
 168 #define _PyObject_VAR_SIZE(typeobj, n) \
 169         ( (typeobj)->tp_basicsize + (n) * (typeobj)->tp_itemsize )
 170
 171 #define PyObject_NEW(type, typeobj) \
 172 ( (type *) PyObject_Init( \
 173         (PyObject *) PyObject_MALLOC( _PyObject_SIZE(typeobj) ), (typeobj)) )
 174 #define PyObject_NEW_VAR(type, typeobj, n) \
 175 ( (type *) PyObject_InitVar( \
 176         (PyVarObject *) PyObject_MALLOC( _PyObject_VAR_SIZE((typeobj),(n)) ),\
 177         (typeobj), (n)) )
 178
 179 #define PyObject_DEL(op) PyObject_FREE(op)
 180
 181 /* This example code implements an object constructor with a custom
 182    allocator, where PyObject_New is inlined, and shows the important
 183    distinction between two steps (at least):
 184        1) the actual allocation of the object storage;
 185        2) the initialization of the Python specific fields
 186           in this storage with PyObject_{Init, InitVar}.
 187
 188    PyObject *
 189    YourObject_New(...)
 190    {
 191        PyObject *op;
 192
 193        op = (PyObject *) Your_Allocator(_PyObject_SIZE(YourTypeStruct));
 194        if (op == NULL)
 195            return PyErr_NoMemory();
 196
 197        op = PyObject_Init(op, &YourTypeStruct);
 198        if (op == NULL)
 199            return NULL;
 200
 201        op->ob_field = value;
 202        ...
 203        return op;
 204    }
 205
 206    Note that in C++, the use of the new operator usually implies that
 207    the 1st step is performed automatically for you, so in a C++ class
 208    constructor you would start directly with PyObject_Init/InitVar. */
 209
 210 /*
 211  * Garbage Collection Support
 212  * ==========================
 213  */
 214
 215 /* To make a new object participate in garbage collection use
 216    PyObject_{New, VarNew, Del} to manage the memory.  Set the type flag
 217    Py_TPFLAGS_GC and define the type method tp_recurse.  You should also
 218    add the method tp_clear if your object is mutable.  Include
 219    PyGC_HEAD_SIZE in the calculation of tp_basicsize.  Call
 220    PyObject_GC_Init after the pointers followed by tp_recurse become
 221    valid (usually just before returning the object from the allocation
 222    method.  Call PyObject_GC_Fini before those pointers become invalid
 223    (usually at the top of the deallocation method).  */
 224
 225 #ifndef WITH_CYCLE_GC
 226
 227 #define PyGC_HEAD_SIZE 0
 228 #define PyObject_GC_Init(op)
 229 #define PyObject_GC_Fini(op)
 230 #define PyObject_AS_GC(op) (op)
 231 #define PyObject_FROM_GC(op) (op)
 232
 233 #else
 234
 235 /* Add the object into the container set */
 236 extern DL_IMPORT(void) _PyGC_Insert(PyObject *);
 237
 238 /* Remove the object from the container set */
 239 extern DL_IMPORT(void) _PyGC_Remove(PyObject *);
 240
 241 #define PyObject_GC_Init(op) _PyGC_Insert((PyObject *)op)
 242 #define PyObject_GC_Fini(op) _PyGC_Remove((PyObject *)op)
 243
 244 /* Structure *prefixed* to container objects participating in GC */
 245 typedef struct _gc_head {
 246         struct _gc_head *gc_next;
 247         struct _gc_head *gc_prev;
 248         int gc_refs;
 249 } PyGC_Head;
 250
 251 #define PyGC_HEAD_SIZE sizeof(PyGC_Head)
 252
 253 /* Test if a type has a GC head */
 254 #define PyType_IS_GC(t) PyType_HasFeature((t), Py_TPFLAGS_GC)
 255
 256 /* Test if an object has a GC head */
 257 #define PyObject_IS_GC(o) PyType_IS_GC((o)->ob_type)
 258
 259 /* Get an object's GC head */
 260 #define PyObject_AS_GC(o) ((PyGC_Head *)(o)-1)
 261
 262 /* Get the object given the PyGC_Head */
 263 #define PyObject_FROM_GC(g) ((PyObject *)(((PyGC_Head *)g)+1))
 264
 265 #endif /* WITH_CYCLE_GC */
 266
 267 #ifdef __cplusplus
 268 }
 269 #endif
 270 #endif /* !Py_OBJIMPL_H */