334 lines
12 KiB
C
334 lines
12 KiB
C
/***********************************************************
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Copyright 1991 by Stichting Mathematisch Centrum, Amsterdam, The
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Netherlands.
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All Rights Reserved
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Permission to use, copy, modify, and distribute this software and its
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documentation for any purpose and without fee is hereby granted,
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provided that the above copyright notice appear in all copies and that
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both that copyright notice and this permission notice appear in
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supporting documentation, and that the names of Stichting Mathematisch
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Centrum or CWI not be used in advertising or publicity pertaining to
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distribution of the software without specific, written prior permission.
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STICHTING MATHEMATISCH CENTRUM DISCLAIMS ALL WARRANTIES WITH REGARD TO
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THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
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FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH CENTRUM BE LIABLE
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FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
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OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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******************************************************************/
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#define NDEBUG
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/* Object and type object interface */
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/*
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123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
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Objects are structures allocated on the heap. Special rules apply to
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the use of objects to ensure they are properly garbage-collected.
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Objects are never allocated statically or on the stack; they must be
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accessed through special macros and functions only. (Type objects are
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exceptions to the first rule; the standard types are represented by
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statically initialized type objects.)
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An object has a 'reference count' that is increased or decreased when a
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pointer to the object is copied or deleted; when the reference count
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reaches zero there are no references to the object left and it can be
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removed from the heap.
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An object has a 'type' that determines what it represents and what kind
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of data it contains. An object's type is fixed when it is created.
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Types themselves are represented as objects; an object contains a
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pointer to the corresponding type object. The type itself has a type
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pointer pointing to the object representing the type 'type', which
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contains a pointer to itself!).
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Objects do not float around in memory; once allocated an object keeps
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the same size and address. Objects that must hold variable-size data
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can contain pointers to variable-size parts of the object. Not all
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objects of the same type have the same size; but the size cannot change
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after allocation. (These restrictions are made so a reference to an
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object can be simply a pointer -- moving an object would require
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updating all the pointers, and changing an object's size would require
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moving it if there was another object right next to it.)
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Objects are always accessed through pointers of the type 'object *'.
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The type 'object' is a structure that only contains the reference count
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and the type pointer. The actual memory allocated for an object
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contains other data that can only be accessed after casting the pointer
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to a pointer to a longer structure type. This longer type must start
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with the reference count and type fields; the macro OB_HEAD should be
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used for this (to accomodate for future changes). The implementation
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of a particular object type can cast the object pointer to the proper
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type and back.
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A standard interface exists for objects that contain an array of items
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whose size is determined when the object is allocated.
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*/
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#ifndef NDEBUG
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/* Turn on heavy reference debugging */
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#define TRACE_REFS
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/* Turn on reference counting */
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#define REF_DEBUG
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#endif /* NDEBUG */
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#ifdef TRACE_REFS
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#define OB_HEAD \
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struct _object *_ob_next, *_ob_prev; \
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int ob_refcnt; \
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struct _typeobject *ob_type;
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#define OB_HEAD_INIT(type) 0, 0, 1, type,
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#else
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#define OB_HEAD \
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unsigned int ob_refcnt; \
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struct _typeobject *ob_type;
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#define OB_HEAD_INIT(type) 1, type,
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#endif
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#define OB_VARHEAD \
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OB_HEAD \
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unsigned int ob_size; /* Number of items in variable part */
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typedef struct _object {
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OB_HEAD
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} object;
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typedef struct {
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OB_VARHEAD
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} varobject;
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/*
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Type objects contain a string containing the type name (to help somewhat
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in debugging), the allocation parameters (see newobj() and newvarobj()),
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and methods for accessing objects of the type. Methods are optional,a
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nil pointer meaning that particular kind of access is not available for
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this type. The DECREF() macro uses the tp_dealloc method without
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checking for a nil pointer; it should always be implemented except if
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the implementation can guarantee that the reference count will never
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reach zero (e.g., for type objects).
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NB: the methods for certain type groups are now contained in separate
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method blocks.
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*/
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typedef struct {
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object *(*nb_add) FPROTO((object *, object *));
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object *(*nb_subtract) FPROTO((object *, object *));
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object *(*nb_multiply) FPROTO((object *, object *));
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object *(*nb_divide) FPROTO((object *, object *));
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object *(*nb_remainder) FPROTO((object *, object *));
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object *(*nb_divmod) FPROTO((object *, object *));
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object *(*nb_power) FPROTO((object *, object *));
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object *(*nb_negative) FPROTO((object *));
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object *(*nb_positive) FPROTO((object *));
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object *(*nb_absolute) FPROTO((object *));
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int (*nb_nonzero) FPROTO((object *));
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object *(*nb_invert) FPROTO((object *));
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object *(*nb_lshift) FPROTO((object *, object *));
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object *(*nb_rshift) FPROTO((object *, object *));
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object *(*nb_and) FPROTO((object *, object *));
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object *(*nb_xor) FPROTO((object *, object *));
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object *(*nb_or) FPROTO((object *, object *));
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} number_methods;
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typedef struct {
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int (*sq_length) FPROTO((object *));
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object *(*sq_concat) FPROTO((object *, object *));
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object *(*sq_repeat) FPROTO((object *, int));
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object *(*sq_item) FPROTO((object *, int));
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object *(*sq_slice) FPROTO((object *, int, int));
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int (*sq_ass_item) FPROTO((object *, int, object *));
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int (*sq_ass_slice) FPROTO((object *, int, int, object *));
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} sequence_methods;
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typedef struct {
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int (*mp_length) FPROTO((object *));
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object *(*mp_subscript) FPROTO((object *, object *));
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int (*mp_ass_subscript) FPROTO((object *, object *, object *));
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} mapping_methods;
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typedef struct _typeobject {
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OB_VARHEAD
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char *tp_name; /* For printing */
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unsigned int tp_basicsize, tp_itemsize; /* For allocation */
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/* Methods to implement standard operations */
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void (*tp_dealloc) FPROTO((object *));
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int (*tp_print) FPROTO((object *, FILE *, int));
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object *(*tp_getattr) FPROTO((object *, char *));
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int (*tp_setattr) FPROTO((object *, char *, object *));
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int (*tp_compare) FPROTO((object *, object *));
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object *(*tp_repr) FPROTO((object *));
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/* Method suites for standard classes */
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number_methods *tp_as_number;
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sequence_methods *tp_as_sequence;
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mapping_methods *tp_as_mapping;
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} typeobject;
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extern typeobject Typetype; /* The type of type objects */
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#define is_typeobject(op) ((op)->ob_type == &Typetype)
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/* Generic operations on objects */
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extern int printobject PROTO((object *, FILE *, int));
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extern object * reprobject PROTO((object *));
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extern int cmpobject PROTO((object *, object *));
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extern object *getattr PROTO((object *, char *));
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extern int setattr PROTO((object *, char *, object *));
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/* Flag bits for printing: */
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#define PRINT_RAW 1 /* No string quotes etc. */
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/*
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The macros INCREF(op) and DECREF(op) are used to increment or decrement
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reference counts. DECREF calls the object's deallocator function; for
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objects that don't contain references to other objects or heap memory
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this can be the standard function free(). Both macros can be used
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whereever a void expression is allowed. The argument shouldn't be a
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NIL pointer. The macro NEWREF(op) is used only to initialize reference
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counts to 1; it is defined here for convenience.
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We assume that the reference count field can never overflow; this can
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be proven when the size of the field is the same as the pointer size
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but even with a 16-bit reference count field it is pretty unlikely so
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we ignore the possibility. (If you are paranoid, make it a long.)
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Type objects should never be deallocated; the type pointer in an object
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is not considered to be a reference to the type object, to save
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complications in the deallocation function. (This is actually a
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decision that's up to the implementer of each new type so if you want,
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you can count such references to the type object.)
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*** WARNING*** The DECREF macro must have a side-effect-free argument
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since it may evaluate its argument multiple times. (The alternative
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would be to mace it a proper function or assign it to a global temporary
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variable first, both of which are slower; and in a multi-threaded
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environment the global variable trick is not safe.)
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*/
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#ifdef TRACE_REFS
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#ifndef REF_DEBUG
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#define REF_DEBUG
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#endif
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#endif
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#ifndef TRACE_REFS
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#define DELREF(op) (*(op)->ob_type->tp_dealloc)((object *)(op))
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#define UNREF(op) /*empty*/
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#endif
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#ifdef REF_DEBUG
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extern long ref_total;
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#ifndef TRACE_REFS
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#define NEWREF(op) (ref_total++, (op)->ob_refcnt = 1)
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#endif
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#define INCREF(op) (ref_total++, (op)->ob_refcnt++)
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#define DECREF(op) \
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if (--ref_total, --(op)->ob_refcnt > 0) \
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; \
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else \
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DELREF(op)
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#else
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#define NEWREF(op) ((op)->ob_refcnt = 1)
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#define INCREF(op) ((op)->ob_refcnt++)
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#define DECREF(op) \
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if (--(op)->ob_refcnt > 0) \
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; \
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else \
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DELREF(op)
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#endif
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/* Macros to use in case the object pointer may be NULL: */
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#define XINCREF(op) if ((op) == NULL) ; else INCREF(op)
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#define XDECREF(op) if ((op) == NULL) ; else DECREF(op)
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/* Definition of NULL, so you don't have to include <stdio.h> */
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#ifndef NULL
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#define NULL 0
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#endif
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/*
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NoObject is an object of undefined type which can be used in contexts
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where NULL (nil) is not suitable (since NULL often means 'error').
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Don't forget to apply INCREF() when returning this value!!!
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*/
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extern object NoObject; /* Don't use this directly */
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#define None (&NoObject)
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/*
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123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
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More conventions
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================
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Argument Checking
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-----------------
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Functions that take objects as arguments normally don't check for nil
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arguments, but they do check the type of the argument, and return an
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error if the function doesn't apply to the type.
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Failure Modes
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-------------
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Functions may fail for a variety of reasons, including running out of
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memory. This is communicated to the caller in two ways: an error string
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is set (see errors.h), and the function result differs: functions that
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normally return a pointer return NULL for failure, functions returning
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an integer return -1 (which could be a legal return value too!), and
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other functions return 0 for success and -1 for failure.
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Callers should always check for errors before using the result.
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Reference Counts
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----------------
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It takes a while to get used to the proper usage of reference counts.
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Functions that create an object set the reference count to 1; such new
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objects must be stored somewhere or destroyed again with DECREF().
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Functions that 'store' objects such as settupleitem() and dictinsert()
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don't increment the reference count of the object, since the most
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frequent use is to store a fresh object. Functions that 'retrieve'
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objects such as gettupleitem() and dictlookup() also don't increment
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the reference count, since most frequently the object is only looked at
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quickly. Thus, to retrieve an object and store it again, the caller
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must call INCREF() explicitly.
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NOTE: functions that 'consume' a reference count like dictinsert() even
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consume the reference if the object wasn't stored, to simplify error
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handling.
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It seems attractive to make other functions that take an object as
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argument consume a reference count; however this may quickly get
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confusing (even the current practice is already confusing). Consider
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it carefully, it may safe lots of calls to INCREF() and DECREF() at
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times.
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123456789-123456789-123456789-123456789-123456789-123456789-123456789-12
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*/
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