/*********************************************************** Copyright 1991 by Stichting Mathematisch Centrum, Amsterdam, The Netherlands. All Rights Reserved Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation, and that the names of Stichting Mathematisch Centrum or CWI not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission. STICHTING MATHEMATISCH CENTRUM DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH CENTRUM BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. ******************************************************************/ #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 */ #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 */