xref: /third_party/python/Include/internal/pycore_pyarena.h

/* An arena-like memory interface for the compiler.
 */

#ifndef Py_INTERNAL_PYARENA_H
#define Py_INTERNAL_PYARENA_H
#ifdef __cplusplus
extern "C" {
#endif

#ifndef Py_BUILD_CORE
#  error "this header requires Py_BUILD_CORE define"
#endif

typedef struct _arena PyArena;

/* _PyArena_New() and _PyArena_Free() create a new arena and free it,
   respectively.  Once an arena has been created, it can be used
   to allocate memory via _PyArena_Malloc().  Pointers to PyObject can
   also be registered with the arena via _PyArena_AddPyObject(), and the
   arena will ensure that the PyObjects stay alive at least until
   _PyArena_Free() is called.  When an arena is freed, all the memory it
   allocated is freed, the arena releases internal references to registered
   PyObject*, and none of its pointers are valid.
   XXX (tim) What does "none of its pointers are valid" mean?  Does it
   XXX mean that pointers previously obtained via _PyArena_Malloc() are
   XXX no longer valid?  (That's clearly true, but not sure that's what
   XXX the text is trying to say.)

   _PyArena_New() returns an arena pointer.  On error, it
   returns a negative number and sets an exception.
   XXX (tim):  Not true.  On error, _PyArena_New() actually returns NULL,
   XXX and looks like it may or may not set an exception (e.g., if the
   XXX internal PyList_New(0) returns NULL, _PyArena_New() passes that on
   XXX and an exception is set; OTOH, if the internal
   XXX block_new(DEFAULT_BLOCK_SIZE) returns NULL, that's passed on but
   XXX an exception is not set in that case).
*/
PyAPI_FUNC(PyArena*) _PyArena_New(void);
PyAPI_FUNC(void) _PyArena_Free(PyArena *);

/* Mostly like malloc(), return the address of a block of memory spanning
 * `size` bytes, or return NULL (without setting an exception) if enough
 * new memory can't be obtained.  Unlike malloc(0), _PyArena_Malloc() with
 * size=0 does not guarantee to return a unique pointer (the pointer
 * returned may equal one or more other pointers obtained from
 * _PyArena_Malloc()).
 * Note that pointers obtained via _PyArena_Malloc() must never be passed to
 * the system free() or realloc(), or to any of Python's similar memory-
 * management functions.  _PyArena_Malloc()-obtained pointers remain valid
 * until _PyArena_Free(ar) is called, at which point all pointers obtained
 * from the arena `ar` become invalid simultaneously.
 */
PyAPI_FUNC(void*) _PyArena_Malloc(PyArena *, size_t size);

/* This routine isn't a proper arena allocation routine.  It takes
 * a PyObject* and records it so that it can be DECREFed when the
 * arena is freed.
 */
PyAPI_FUNC(int) _PyArena_AddPyObject(PyArena *, PyObject *);

#ifdef __cplusplus
}
#endif
#endif /* !Py_INTERNAL_PYARENA_H */