objimpl.h revision 91a681debf9ffec155d0aff8a0bb5f965f592e16
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 11extern "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/* 27Functions 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 49Note that objects created with PyObject_{New, NewVar} are allocated using the 50specialized Python allocator (implemented in obmalloc.c), if WITH_PYMALLOC is 51enabled. In addition, a special debugging allocator is used if PYMALLOC_DEBUG 52is also #defined. 53 54In case a specific form of memory management is needed (for example, if you 55must use the platform malloc heap(s), or shared memory, or C++ local storage or 56operator new), you must first allocate the object with your custom allocator, 57then pass its pointer to PyObject_{Init, InitVar} for filling in its Python- 58specific fields: reference count, type pointer, possibly others. You should 59be aware that Python no control over these objects because they don't 60cooperate with the Python memory manager. Such objects may not be eligible 61for automatic garbage collection and you have to make sure that they are 62released accordingly whenever their destructor gets called (cf. the specific 63form of memory management you're using). 64 65Unless you have specific memory management requirements, use 66PyObject_{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*/ 97PyAPI_FUNC(void *) PyObject_Malloc(size_t); 98PyAPI_FUNC(void *) PyObject_Realloc(void *, size_t); 99PyAPI_FUNC(void) PyObject_Free(void *); 100 101 102/* Macros */ 103#ifdef WITH_PYMALLOC 104#ifdef PYMALLOC_DEBUG 105PyAPI_FUNC(void *) _PyObject_DebugMalloc(size_t nbytes); 106PyAPI_FUNC(void *) _PyObject_DebugRealloc(void *p, size_t nbytes); 107PyAPI_FUNC(void) _PyObject_DebugFree(void *p); 108PyAPI_FUNC(void) _PyObject_DebugDumpAddress(const void *p); 109PyAPI_FUNC(void) _PyObject_DebugCheckAddress(const void *p); 110PyAPI_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 compatability 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 */ 147PyAPI_FUNC(PyObject *) PyObject_Init(PyObject *, PyTypeObject *); 148PyAPI_FUNC(PyVarObject *) PyObject_InitVar(PyVarObject *, 149 PyTypeObject *, int); 150PyAPI_FUNC(PyObject *) _PyObject_New(PyTypeObject *); 151PyAPI_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/* Test if a type has a GC head */ 232#define PyType_IS_GC(t) PyType_HasFeature((t), Py_TPFLAGS_HAVE_GC) 233 234/* Test if an object has a GC head */ 235#define PyObject_IS_GC(o) (PyType_IS_GC((o)->ob_type) && \ 236 ((o)->ob_type->tp_is_gc == NULL || (o)->ob_type->tp_is_gc(o))) 237 238PyAPI_FUNC(PyVarObject *) _PyObject_GC_Resize(PyVarObject *, int); 239#define PyObject_GC_Resize(type, op, n) \ 240 ( (type *) _PyObject_GC_Resize((PyVarObject *)(op), (n)) ) 241 242/* for source compatibility with 2.2 */ 243#define _PyObject_GC_Del PyObject_GC_Del 244 245/* GC information is stored BEFORE the object structure. */ 246typedef union _gc_head { 247 struct { 248 union _gc_head *gc_next; 249 union _gc_head *gc_prev; 250 int gc_refs; 251 } gc; 252 long double dummy; /* force worst-case alignment */ 253} PyGC_Head; 254 255extern PyGC_Head *_PyGC_generation0; 256 257#define _Py_AS_GC(o) ((PyGC_Head *)(o)-1) 258 259#define _PyGC_REFS_UNTRACKED (-2) 260#define _PyGC_REFS_REACHABLE (-3) 261#define _PyGC_REFS_TENTATIVELY_UNREACHABLE (-4) 262 263/* Tell the GC to track this object. NB: While the object is tracked the 264 * collector it must be safe to call the ob_traverse method. */ 265#define _PyObject_GC_TRACK(o) do { \ 266 PyGC_Head *g = _Py_AS_GC(o); \ 267 if (g->gc.gc_refs != _PyGC_REFS_UNTRACKED) \ 268 Py_FatalError("GC object already tracked"); \ 269 g->gc.gc_refs = _PyGC_REFS_REACHABLE; \ 270 g->gc.gc_next = _PyGC_generation0; \ 271 g->gc.gc_prev = _PyGC_generation0->gc.gc_prev; \ 272 g->gc.gc_prev->gc.gc_next = g; \ 273 _PyGC_generation0->gc.gc_prev = g; \ 274 } while (0); 275 276/* Tell the GC to stop tracking this object. 277 * gc_next doesn't need to be set to NULL, but doing so is a good 278 * way to provoke memory errors if calling code is confused. 279 */ 280#define _PyObject_GC_UNTRACK(o) do { \ 281 PyGC_Head *g = _Py_AS_GC(o); \ 282 assert(g->gc.gc_refs != _PyGC_REFS_UNTRACKED); \ 283 g->gc.gc_refs = _PyGC_REFS_UNTRACKED; \ 284 g->gc.gc_prev->gc.gc_next = g->gc.gc_next; \ 285 g->gc.gc_next->gc.gc_prev = g->gc.gc_prev; \ 286 g->gc.gc_next = NULL; \ 287 } while (0); 288 289PyAPI_FUNC(PyObject *) _PyObject_GC_Malloc(size_t); 290PyAPI_FUNC(PyObject *) _PyObject_GC_New(PyTypeObject *); 291PyAPI_FUNC(PyVarObject *) _PyObject_GC_NewVar(PyTypeObject *, int); 292PyAPI_FUNC(void) PyObject_GC_Track(void *); 293PyAPI_FUNC(void) PyObject_GC_UnTrack(void *); 294PyAPI_FUNC(void) PyObject_GC_Del(void *); 295 296#define PyObject_GC_New(type, typeobj) \ 297 ( (type *) _PyObject_GC_New(typeobj) ) 298#define PyObject_GC_NewVar(type, typeobj, n) \ 299 ( (type *) _PyObject_GC_NewVar((typeobj), (n)) ) 300 301 302/* This is here for the sake of backwards compatibility. Extensions that 303 * use the old GC API will still compile but the objects will not be 304 * tracked by the GC. */ 305#define PyGC_HEAD_SIZE 0 306#define PyObject_GC_Init(op) 307#define PyObject_GC_Fini(op) 308#define PyObject_AS_GC(op) (op) 309#define PyObject_FROM_GC(op) (op) 310 311 312/* Test if a type supports weak references */ 313#define PyType_SUPPORTS_WEAKREFS(t) \ 314 (PyType_HasFeature((t), Py_TPFLAGS_HAVE_WEAKREFS) \ 315 && ((t)->tp_weaklistoffset > 0)) 316 317#define PyObject_GET_WEAKREFS_LISTPTR(o) \ 318 ((PyObject **) (((char *) (o)) + (o)->ob_type->tp_weaklistoffset)) 319 320#ifdef __cplusplus 321} 322#endif 323#endif /* !Py_OBJIMPL_H */ 324