And so, we are saved.
+Except see also BREAK-VICIOUS-METACIRCLE. -- CSR, 2003-05-28
+
|#
\f
;;; an alist in which each entry is of the form
collect))))
(nreverse collect)))))
\f
+;;; Standardized class slot access: when trying to break vicious
+;;; metacircles, we need a way to get at the values of slots of some
+;;; standard classes without going through the whole meta machinery,
+;;; because that would likely enter the vicious circle again. The
+;;; following are helper functions that short-circuit the generic
+;;; lookup machinery.
+
+(defvar *standard-classes*
+ '(standard-method standard-generic-function standard-class
+ standard-effective-slot-definition))
+
+(defvar *standard-slot-locations* (make-hash-table :test 'equal))
+
+(defun compute-standard-slot-locations ()
+ (clrhash *standard-slot-locations*)
+ (dolist (class-name *standard-classes*)
+ (let ((class (find-class class-name)))
+ (dolist (slot (class-slots class))
+ (setf (gethash (cons class (slot-definition-name slot))
+ *standard-slot-locations*)
+ (slot-definition-location slot))))))
+
+;;; FIXME: harmonize the names between COMPUTE-STANDARD-SLOT-LOCATIONS
+;;; and MAYBE-UPDATE-STANDARD-CLASS-LOCATIONS.
+(defun maybe-update-standard-class-locations (class)
+ (when (and (eq *boot-state* 'complete)
+ (memq (class-name class) *standard-classes*))
+ (compute-standard-slot-locations)))
+
+(defun standard-slot-value (object slot-name class)
+ (let ((location (gethash (cons class slot-name) *standard-slot-locations*)))
+ (if location
+ (let ((value (if (funcallable-instance-p object)
+ (funcallable-standard-instance-access object location)
+ (standard-instance-access object location))))
+ (when (eq +slot-unbound+ value)
+ (error "~@<slot ~s of class ~s is unbound in object ~s~@:>"
+ slot-name class object))
+ value)
+ (error "~@<cannot get standard value of slot ~s of class ~s ~
+ in object ~s~@:>"
+ slot-name class object))))
+
+(defun standard-slot-value/gf (gf slot-name)
+ (standard-slot-value gf slot-name *the-class-standard-generic-function*))
+
+(defun standard-slot-value/method (method slot-name)
+ (standard-slot-value method slot-name *the-class-standard-method*))
+
+(defun standard-slot-value/eslotd (slotd slot-name)
+ (standard-slot-value slotd slot-name
+ *the-class-standard-effective-slot-definition*))
+
+(defun standard-slot-value/class (class slot-name)
+ (standard-slot-value class slot-name *the-class-standard-class*))
+\f
;;; When all the methods of a generic function are automatically
;;; generated reader or writer methods a number of special
;;; optimizations are possible. These are important because of the
;;; <index> If <type> is READER or WRITER, and the slot accessed is
;;; an :instance slot, this is the index number of that slot
;;; in the object argument.
+(defvar *cache-miss-values-stack* ())
+
(defun cache-miss-values (gf args state)
(multiple-value-bind (nreq applyp metatypes nkeys arg-info)
(get-generic-fun-info gf)
accessor-type index)))))
(defun cache-miss-values-internal (gf arg-info wrappers classes types state)
+ (if (and classes (equal classes (cdr (assq gf *cache-miss-values-stack*))))
+ (break-vicious-metacircle gf classes arg-info)
+ (let ((*cache-miss-values-stack*
+ (acons gf classes *cache-miss-values-stack*))
+ (cam-std-p (or (null arg-info)
+ (gf-info-c-a-m-emf-std-p arg-info))))
+ (multiple-value-bind (methods all-applicable-and-sorted-p)
+ (if cam-std-p
+ (compute-applicable-methods-using-types gf types)
+ (compute-applicable-methods-using-classes gf classes))
+
(let* ((for-accessor-p (eq state 'accessor))
(for-cache-p (or (eq state 'caching) (eq state 'accessor)))
- (cam-std-p (or (null arg-info)
- (gf-info-c-a-m-emf-std-p arg-info))))
- (multiple-value-bind (methods all-applicable-and-sorted-p)
- (if cam-std-p
- (compute-applicable-methods-using-types gf types)
- (compute-applicable-methods-using-classes gf classes))
- (let ((emf (if (or cam-std-p all-applicable-and-sorted-p)
- (function-funcall (get-secondary-dispatch-function1
- gf methods types nil (and for-cache-p
- wrappers)
- all-applicable-and-sorted-p)
- nil (and for-cache-p wrappers))
- (default-secondary-dispatch-function gf))))
- (multiple-value-bind (index accessor-type)
- (and for-accessor-p all-applicable-and-sorted-p methods
- (accessor-values gf arg-info classes methods))
- (values (if (integerp index) index emf)
- methods accessor-type index))))))
+ (emf (if (or cam-std-p all-applicable-and-sorted-p)
+ (function-funcall (get-secondary-dispatch-function1
+ gf methods types nil (and for-cache-p
+ wrappers)
+ all-applicable-and-sorted-p)
+ nil (and for-cache-p wrappers))
+ (default-secondary-dispatch-function gf))))
+ (multiple-value-bind (index accessor-type)
+ (and for-accessor-p all-applicable-and-sorted-p methods
+ (accessor-values gf arg-info classes methods))
+ (values (if (integerp index) index emf)
+ methods accessor-type index)))))))
+
+;;; Try to break a vicious circle while computing a cache miss.
+;;; GF is the generic function, CLASSES are the classes of actual
+;;; arguments, and ARG-INFO is the generic functions' arg-info.
+;;;
+;;; A vicious circle can be entered when the computation of the cache
+;;; miss values itself depends on the values being computed. For
+;;; instance, adding a method which is an instance of a subclass of
+;;; STANDARD-METHOD leads to cache misses for slot accessors of
+;;; STANDARD-METHOD like METHOD-SPECIALIZERS, and METHOD-SPECIALIZERS
+;;; is itself used while we compute cache miss values.
+(defun break-vicious-metacircle (gf classes arg-info)
+ (when (typep gf 'standard-generic-function)
+ (multiple-value-bind (class slotd accessor-type)
+ (accesses-standard-class-slot-p gf)
+ (when class
+ (let ((method (find-standard-class-accessor-method
+ gf class accessor-type))
+ (index (standard-slot-value/eslotd slotd 'location))
+ (type (gf-info-simple-accessor-type arg-info)))
+ (when (and method
+ (subtypep (ecase accessor-type
+ ((reader) (car classes))
+ ((writer) (cadr classes)))
+ class))
+ (return-from break-vicious-metacircle
+ (values index (list method) type index)))))))
+ (error "~@<vicious metacircle: The computation of an ~
+ effective method of ~s for arguments of types ~s uses ~
+ the effective method being computed.~@:>"
+ gf classes))
+
+;;; Return (CLASS SLOTD ACCESSOR-TYPE) if some method of generic
+;;; function GF accesses a slot of some class in *STANDARD-CLASSES*.
+;;; CLASS is the class accessed, SLOTD is the effective slot definition
+;;; object of the slot accessed, and ACCESSOR-TYPE is one of the symbols
+;;; READER or WRITER describing the slot access.
+(defun accesses-standard-class-slot-p (gf)
+ (flet ((standard-class-slot-access (gf class)
+ (loop with gf-name = (standard-slot-value/gf gf 'name)
+ for slotd in (standard-slot-value/class class 'slots)
+ ;; FIXME: where does BOUNDP fit in here? Is it
+ ;; relevant?
+ as readers = (standard-slot-value/eslotd slotd 'readers)
+ as writers = (standard-slot-value/eslotd slotd 'writers)
+ if (member gf-name readers :test #'equal)
+ return (values slotd 'reader)
+ else if (member gf-name writers :test #'equal)
+ return (values slotd 'writer))))
+ (dolist (class-name *standard-classes*)
+ (let ((class (find-class class-name)))
+ (multiple-value-bind (slotd accessor-type)
+ (standard-class-slot-access gf class)
+ (when slotd
+ (return (values class slotd accessor-type))))))))
+
+;;; Find a slot reader/writer method among the methods of generic
+;;; function GF which reads/writes instances of class CLASS.
+;;; TYPE is one of the symbols READER or WRITER.
+(defun find-standard-class-accessor-method (gf class type)
+ (dolist (method (standard-slot-value/gf gf 'methods))
+ (let ((specializers (standard-slot-value/method method 'specializers))
+ (qualifiers (plist-value method 'qualifiers)))
+ (when (and (null qualifiers)
+ (eq (ecase type
+ (reader (car specializers))
+ (writer (cadr specializers)))
+ class))
+ (return method)))))
(defun accessor-values (gf arg-info classes methods)
(declare (ignore gf))
projects / sbcl.git / commitdiff