mirror of https://github.com/python/cpython
301 lines
10 KiB
C
301 lines
10 KiB
C
#define NDEBUG
|
|
/* Object and type object interface */
|
|
|
|
/*
|
|
123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
|
|
|
|
Objects are structures allocated on the heap. Special rules apply to
|
|
the use of objects to ensure they are properly garbage-collected.
|
|
Objects are never allocated statically or on the stack; they must be
|
|
accessed through special macros and functions only. (Type objects are
|
|
exceptions to the first rule; the standard types are represented by
|
|
statically initialized type objects.)
|
|
|
|
An object has a 'reference count' that is increased or decreased when a
|
|
pointer to the object is copied or deleted; when the reference count
|
|
reaches zero there are no references to the object left and it can be
|
|
removed from the heap.
|
|
|
|
An object has a 'type' that determines what it represents and what kind
|
|
of data it contains. An object's type is fixed when it is created.
|
|
Types themselves are represented as objects; an object contains a
|
|
pointer to the corresponding type object. The type itself has a type
|
|
pointer pointing to the object representing the type 'type', which
|
|
contains a pointer to itself!).
|
|
|
|
Objects do not float around in memory; once allocated an object keeps
|
|
the same size and address. Objects that must hold variable-size data
|
|
can contain pointers to variable-size parts of the object. Not all
|
|
objects of the same type have the same size; but the size cannot change
|
|
after allocation. (These restrictions are made so a reference to an
|
|
object can be simply a pointer -- moving an object would require
|
|
updating all the pointers, and changing an object's size would require
|
|
moving it if there was another object right next to it.)
|
|
|
|
Objects are always accessed through pointers of the type 'object *'.
|
|
The type 'object' is a structure that only contains the reference count
|
|
and the type pointer. The actual memory allocated for an object
|
|
contains other data that can only be accessed after casting the pointer
|
|
to a pointer to a longer structure type. This longer type must start
|
|
with the reference count and type fields; the macro OB_HEAD should be
|
|
used for this (to accomodate for future changes). The implementation
|
|
of a particular object type can cast the object pointer to the proper
|
|
type and back.
|
|
|
|
A standard interface exists for objects that contain an array of items
|
|
whose size is determined when the object is allocated.
|
|
|
|
123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
|
|
*/
|
|
|
|
#ifndef NDEBUG
|
|
|
|
/* Turn on heavy reference debugging */
|
|
#define TRACE_REFS
|
|
|
|
/* Turn on reference counting */
|
|
#define REF_DEBUG
|
|
|
|
#endif /* NDEBUG */
|
|
|
|
#ifdef TRACE_REFS
|
|
#define OB_HEAD \
|
|
struct _object *_ob_next, *_ob_prev; \
|
|
int ob_refcnt; \
|
|
struct _typeobject *ob_type;
|
|
#define OB_HEAD_INIT(type) 0, 0, 1, type,
|
|
#else
|
|
#define OB_HEAD \
|
|
unsigned int ob_refcnt; \
|
|
struct _typeobject *ob_type;
|
|
#define OB_HEAD_INIT(type) 1, type,
|
|
#endif
|
|
|
|
#define OB_VARHEAD \
|
|
OB_HEAD \
|
|
unsigned int ob_size; /* Number of items in variable part */
|
|
|
|
typedef struct _object {
|
|
OB_HEAD
|
|
} object;
|
|
|
|
typedef struct {
|
|
OB_VARHEAD
|
|
} varobject;
|
|
|
|
|
|
/*
|
|
123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
|
|
|
|
Type objects contain a string containing the type name (to help somewhat
|
|
in debugging), the allocation parameters (see newobj() and newvarobj()),
|
|
and methods for accessing objects of the type. Methods are optional,a
|
|
nil pointer meaning that particular kind of access is not available for
|
|
this type. The DECREF() macro uses the tp_dealloc method without
|
|
checking for a nil pointer; it should always be implemented except if
|
|
the implementation can guarantee that the reference count will never
|
|
reach zero (e.g., for type objects).
|
|
|
|
NB: the methods for certain type groups are now contained in separate
|
|
method blocks.
|
|
*/
|
|
|
|
typedef struct {
|
|
object *(*nb_add) FPROTO((object *, object *));
|
|
object *(*nb_subtract) FPROTO((object *, object *));
|
|
object *(*nb_multiply) FPROTO((object *, object *));
|
|
object *(*nb_divide) FPROTO((object *, object *));
|
|
object *(*nb_remainder) FPROTO((object *, object *));
|
|
object *(*nb_power) FPROTO((object *, object *));
|
|
object *(*nb_negative) FPROTO((object *));
|
|
object *(*nb_positive) FPROTO((object *));
|
|
} number_methods;
|
|
|
|
typedef struct {
|
|
int (*sq_length) FPROTO((object *));
|
|
object *(*sq_concat) FPROTO((object *, object *));
|
|
object *(*sq_repeat) FPROTO((object *, int));
|
|
object *(*sq_item) FPROTO((object *, int));
|
|
object *(*sq_slice) FPROTO((object *, int, int));
|
|
int (*sq_ass_item) FPROTO((object *, int, object *));
|
|
int (*sq_ass_slice) FPROTO((object *, int, int, object *));
|
|
} sequence_methods;
|
|
|
|
typedef struct {
|
|
int (*mp_length) FPROTO((object *));
|
|
object *(*mp_subscript) FPROTO((object *, object *));
|
|
int (*mp_ass_subscript) FPROTO((object *, object *, object *));
|
|
} mapping_methods;
|
|
|
|
typedef struct _typeobject {
|
|
OB_VARHEAD
|
|
char *tp_name; /* For printing */
|
|
unsigned int tp_basicsize, tp_itemsize; /* For allocation */
|
|
|
|
/* Methods to implement standard operations */
|
|
|
|
void (*tp_dealloc) FPROTO((object *));
|
|
void (*tp_print) FPROTO((object *, FILE *, int));
|
|
object *(*tp_getattr) FPROTO((object *, char *));
|
|
int (*tp_setattr) FPROTO((object *, char *, object *));
|
|
int (*tp_compare) FPROTO((object *, object *));
|
|
object *(*tp_repr) FPROTO((object *));
|
|
|
|
/* Method suites for standard classes */
|
|
|
|
number_methods *tp_as_number;
|
|
sequence_methods *tp_as_sequence;
|
|
mapping_methods *tp_as_mapping;
|
|
} typeobject;
|
|
|
|
extern typeobject Typetype; /* The type of type objects */
|
|
|
|
#define is_typeobject(op) ((op)->ob_type == &Typetype)
|
|
|
|
/* Generic operations on objects */
|
|
extern void printobject PROTO((object *, FILE *, int));
|
|
extern object * reprobject PROTO((object *));
|
|
extern int cmpobject PROTO((object *, object *));
|
|
extern object *getattr PROTO((object *, char *));
|
|
extern int setattr PROTO((object *, char *, object *));
|
|
|
|
/* Flag bits for printing: */
|
|
#define PRINT_RAW 1 /* No string quotes etc. */
|
|
|
|
/*
|
|
123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
|
|
|
|
The macros INCREF(op) and DECREF(op) are used to increment or decrement
|
|
reference counts. DECREF calls the object's deallocator function; for
|
|
objects that don't contain references to other objects or heap memory
|
|
this can be the standard function free(). Both macros can be used
|
|
whereever a void expression is allowed. The argument shouldn't be a
|
|
NIL pointer. The macro NEWREF(op) is used only to initialize reference
|
|
counts to 1; it is defined here for convenience.
|
|
|
|
We assume that the reference count field can never overflow; this can
|
|
be proven when the size of the field is the same as the pointer size
|
|
but even with a 16-bit reference count field it is pretty unlikely so
|
|
we ignore the possibility. (If you are paranoid, make it a long.)
|
|
|
|
Type objects should never be deallocated; the type pointer in an object
|
|
is not considered to be a reference to the type object, to save
|
|
complications in the deallocation function. (This is actually a
|
|
decision that's up to the implementer of each new type so if you want,
|
|
you can count such references to the type object.)
|
|
|
|
*** WARNING*** The DECREF macro must have a side-effect-free argument
|
|
since it may evaluate its argument multiple times. (The alternative
|
|
would be to mace it a proper function or assign it to a global temporary
|
|
variable first, both of which are slower; and in a multi-threaded
|
|
environment the global variable trick is not safe.)
|
|
*/
|
|
|
|
#ifdef TRACE_REFS
|
|
#ifndef REF_DEBUG
|
|
#define REF_DEBUG
|
|
#endif
|
|
#endif
|
|
|
|
#ifndef TRACE_REFS
|
|
#define DELREF(op) (*(op)->ob_type->tp_dealloc)((object *)(op))
|
|
#define UNREF(op) /*empty*/
|
|
#endif
|
|
|
|
#ifdef REF_DEBUG
|
|
extern long ref_total;
|
|
#ifndef TRACE_REFS
|
|
#define NEWREF(op) (ref_total++, (op)->ob_refcnt = 1)
|
|
#endif
|
|
#define INCREF(op) (ref_total++, (op)->ob_refcnt++)
|
|
#define DECREF(op) \
|
|
if (--ref_total, --(op)->ob_refcnt > 0) \
|
|
; \
|
|
else \
|
|
DELREF(op)
|
|
#else
|
|
#define NEWREF(op) ((op)->ob_refcnt = 1)
|
|
#define INCREF(op) ((op)->ob_refcnt++)
|
|
#define DECREF(op) \
|
|
if (--(op)->ob_refcnt > 0) \
|
|
; \
|
|
else \
|
|
DELREF(op)
|
|
#endif
|
|
|
|
/* Macros to use in case the object pointer may be NULL: */
|
|
|
|
#define XINCREF(op) if ((op) == NULL) ; else INCREF(op)
|
|
#define XDECREF(op) if ((op) == NULL) ; else DECREF(op)
|
|
|
|
/* Definition of NULL, so you don't have to include <stdio.h> */
|
|
|
|
#ifndef NULL
|
|
#define NULL 0
|
|
#endif
|
|
|
|
|
|
/*
|
|
NoObject is an object of undefined type which can be used in contexts
|
|
where NULL (nil) is not suitable (since NULL often means 'error').
|
|
|
|
Don't forget to apply INCREF() when returning this value!!!
|
|
*/
|
|
|
|
extern object NoObject; /* Don't use this directly */
|
|
|
|
#define None (&NoObject)
|
|
|
|
|
|
/*
|
|
123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
|
|
|
|
More conventions
|
|
================
|
|
|
|
Argument Checking
|
|
-----------------
|
|
|
|
Functions that take objects as arguments normally don't check for nil
|
|
arguments, but they do check the type of the argument, and return an
|
|
error if the function doesn't apply to the type.
|
|
|
|
Failure Modes
|
|
-------------
|
|
|
|
Functions may fail for a variety of reasons, including running out of
|
|
memory. This is communicated to the caller in two ways: an error string
|
|
is set (see errors.h), and the function result differs: functions that
|
|
normally return a pointer return NULL for failure, functions returning
|
|
an integer return -1 (which could be a legal return value too!), and
|
|
other functions return 0 for success and -1 for failure.
|
|
Callers should always check for errors before using the result.
|
|
|
|
Reference Counts
|
|
----------------
|
|
|
|
It takes a while to get used to the proper usage of reference counts.
|
|
|
|
Functions that create an object set the reference count to 1; such new
|
|
objects must be stored somewhere or destroyed again with DECREF().
|
|
Functions that 'store' objects such as settupleitem() and dictinsert()
|
|
don't increment the reference count of the object, since the most
|
|
frequent use is to store a fresh object. Functions that 'retrieve'
|
|
objects such as gettupleitem() and dictlookup() also don't increment
|
|
the reference count, since most frequently the object is only looked at
|
|
quickly. Thus, to retrieve an object and store it again, the caller
|
|
must call INCREF() explicitly.
|
|
|
|
NOTE: functions that 'consume' a reference count like dictinsert() even
|
|
consume the reference if the object wasn't stored, to simplify error
|
|
handling.
|
|
|
|
It seems attractive to make other functions that take an object as
|
|
argument consume a reference count; however this may quickly get
|
|
confusing (even the current practice is already confusing). Consider
|
|
it carefully, it may safe lots of calls to INCREF() and DECREF() at
|
|
times.
|
|
|
|
123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
|
|
*/
|