3 ;;; Method combination protocol
5 ;;; (c) 2009 Straylight/Edgeware
8 ;;;----- Licensing notice ---------------------------------------------------
10 ;;; This file is part of the Sensible Object Design, an object system for C.
12 ;;; SOD is free software; you can redistribute it and/or modify
13 ;;; it under the terms of the GNU General Public License as published by
14 ;;; the Free Software Foundation; either version 2 of the License, or
15 ;;; (at your option) any later version.
17 ;;; SOD is distributed in the hope that it will be useful,
18 ;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
19 ;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 ;;; GNU General Public License for more details.
22 ;;; You should have received a copy of the GNU General Public License
23 ;;; along with SOD; if not, write to the Free Software Foundation,
24 ;;; Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
28 ;;;--------------------------------------------------------------------------
29 ;;; Effective methods and entries.
31 (export '(effective-method
32 effective-method-message effective-method-class
33 effective-method-keywords))
34 (defclass effective-method ()
35 ((message :initarg :message :type sod-message
36 :reader effective-method-message)
37 (%class :initarg :class :type sod-class :reader effective-method-class)
38 (keywords :type list :reader effective-method-keywords))
40 "The behaviour invoked by sending a message to an instance of a class.
42 This class describes the behaviour when an instance of CLASS is sent
45 This is not a useful class by itself. Message classes are expected to
46 define their own effective-method classes.
48 An effective method class may accept a `:direct-methods' initarg, which
49 will be a list of applicable methods sorted in most-to-least specific
52 (export 'sod-message-effective-method-class)
53 (defgeneric sod-message-effective-method-class (message)
55 "Return the effective method class for the given MESSAGE.
57 This function is invoked by `compute-sod-effective-method'."))
59 (export 'primary-method-class)
60 (defgeneric primary-method-class (message)
62 "Return the name of the primary direct method class for MESSAGE.
64 This protocol is used by `simple-message' subclasses."))
66 (export 'method-keyword-argument-lists)
67 (defgeneric method-keyword-argument-lists (method direct-methods)
69 "Returns a list of keyword argument lists to be merged.
71 This should return a list suitable for passing to `merge-keyword-lists',
72 i.e., each element should be a pair consisting of a list of `argument'
73 objects and a string describing the source of the argument list."))
75 (export 'compute-sod-effective-method)
76 (defgeneric compute-sod-effective-method (message class)
78 "Return the effective method when a CLASS instance receives MESSAGE.
80 The default method constructs an instance of the message's chosen
81 `sod-message-effective-method-class', passing the MESSAGE, the CLASS and
82 the list of applicable methods as initargs to `make-instance'."))
84 (export 'compute-effective-methods)
85 (defgeneric compute-effective-methods (class)
87 "Return a list of all of the effective methods needed for CLASS.
89 The list needn't be in any particular order."))
91 (export '(method-entry method-entry-effective-method
92 method-entry-chain-head method-entry-chain-tail))
93 (defclass method-entry ()
94 ((%method :initarg :method :type effective-method
95 :reader method-entry-effective-method)
96 (chain-head :initarg :chain-head :type sod-class
97 :reader method-entry-chain-head)
98 (chain-tail :initarg :chain-tail :type sod-class
99 :reader method-entry-chain-tail)
100 (role :initarg :role :type (or keyword null) :reader method-entry-role))
102 "An entry point into an effective method.
104 Specifically, this is the entry point to the effective METHOD invoked via
105 the vtable for the chain headed by CHAIN-HEAD, and serving the given ROLE.
106 The CHAIN-TAIL is the most specific class on this chain; this is useful
107 because we can reuse the types of method entries from superclasses on
110 Each effective method may have several different method entries, because
111 an effective method can be called via vtables attached to different
112 chains, and such calls will pass instance pointers which point to
113 different `ichain' structures within the overall instance layout; it's the
114 job of the method entry to adjust the instance pointers correctly for the
115 rest of the effective method.
117 A vtable can contain more than one entry for the same message. Such
118 entries are distinguished by their roles. A message always has an entry
119 with the `nil role; in addition, a varargs message also has a `:valist'
120 role, which accepts a `va_list' argument in place of the variable argument
121 listNo other roles are currently defined, though they may be introduced by
124 The boundaries between a method entry and the effective method
125 is (intentionally) somewhat fuzzy. In extreme cases, the effective method
126 may not exist at all as a distinct entity in the output because its
127 content is duplicated in all of the method entry functions. This is left
128 up to the effective method protocol."))
130 (export 'make-method-entries)
131 (defgeneric make-method-entries (effective-method chain-head chain-tail)
133 "Return a list of `method-entry' objects for an EFFECTIVE-METHOD called
136 There is no default method for this function. (Maybe when the
137 effective-method/method-entry output protocol has settled down I'll know
138 what a sensible default action would be.)"))
140 ;;;--------------------------------------------------------------------------
141 ;;; Protocol for messages and direct-methods.
143 (export 'sod-message-argument-tail)
144 (defgeneric sod-message-argument-tail (message)
146 "Return the argument tail for the message, with invented argument names.
148 No `me' argument is prepended; any `:ellipsis' is left as it is."))
150 (export 'sod-method-description)
151 (defgeneric sod-method-description (method)
153 "Return an adjectival phrase describing METHOD.
155 The result will be placed into an error message reading something like
156 ``Conflicting definition of DESCRIPTION direct method `bogus'''. Two
157 direct methods which can coexist in the same class, defined on the same
158 message, should have differing descriptions."))
160 (export 'sod-method-function-type)
161 (defgeneric sod-method-function-type (method)
163 "Return the C function type for the direct method.
165 This is called during initialization of a direct method object, and the
168 A default method is provided (by `basic-direct-method') which simply
169 prepends an appropriate `me' argument to the user-provided argument list.
170 Fancy method classes may need to override this behaviour."))
172 (export 'sod-method-next-method-type)
173 (defgeneric sod-method-next-method-type (method)
175 "Return the C function type for the next-method trampoline.
177 This is called during initialization of a direct method object, and the
178 result is cached. It should return a function type, not a pointer type.
180 A default method is provided (by `delegating-direct-method') which should
181 do the right job. Very fancy subclasses might need to do something
184 (export 'sod-method-function-name)
185 (defgeneric sod-method-function-name (method)
187 "Return the C function name for the direct method."))
189 (export 'keyword-message-p)
190 (defun keyword-message-p (message)
191 "Answer whether the MESSAGE accepts a keyword arguments.
193 Dealing with keyword messages is rather fiddly, so this is useful to
195 (typep (sod-message-type message) 'c-keyword-function-type))
197 (export 'varargs-message-p)
198 (defun varargs-message-p (message)
199 "Answer whether the MESSAGE accepts a variable-length argument list.
201 We need to jump through some extra hoops in order to cope with varargs
202 messages, so this is useful to know."
203 (member :ellipsis (sod-message-argument-tail message)))
205 ;;;--------------------------------------------------------------------------
206 ;;; Protocol for effective methods and method entries.
208 (export 'method-entry-function-type)
209 (defgeneric method-entry-function-type (entry)
211 "Return the C function type for a method entry."))
213 (export 'method-entry-slot-name)
214 (defgeneric method-entry-slot-name (entry)
216 "Return the `vtmsgs' slot name for a method entry.
218 The default method indirects through `method-entry-slot-name-by-role'."))
220 (defgeneric method-entry-slot-name-by-role (entry role name)
221 (:documentation "Easier implementation for `method-entry-slot-name'.")
222 (:method ((entry method-entry) (role (eql nil)) name) name)
223 (:method ((entry method-entry) (role (eql :valist)) name)
224 (format nil "~A__v" name)))
226 (export 'effective-method-basic-argument-names)
227 (defgeneric effective-method-basic-argument-names (method)
229 "Return a list of argument names to be passed to direct methods.
231 The argument names are constructed from the message's arguments returned
232 by `sod-message-argument-tail', with any ellipsis replaced by an explicit
233 `va_list' argument. The basic arguments are the ones immediately derived
234 from the programmer's explicitly stated arguments; the `me' argument is
235 not included, and neither are more exotic arguments added as part of the
236 method delegation protocol."))
238 (export 'effective-method-live-p)
239 (defgeneric effective-method-live-p (method)
241 "Returns true if the effective METHOD is live.
243 An effective method is `live' if it should actually have proper method entry
244 functions associated with it and stored in the class vtable. The other
245 possibility is that the method is `dead', in which case the function
246 pointers in the vtable are left null."))
248 ;;;--------------------------------------------------------------------------
251 ;;; Enhanced code-generator class.
253 (export '(method-codegen codegen-message codegen-class
254 codegen-method codegen-target))
255 (defclass method-codegen (codegen)
256 ((message :initarg :message :type sod-message :reader codegen-message)
257 (%class :initarg :class :type sod-class :reader codegen-class)
258 (%method :initarg :method :type effective-method :reader codegen-method)
259 (target :initarg :target :reader codegen-target))
261 "Augments CODEGEN with additional state regarding an effective method.
263 We store the effective method, and also its target class and owning
264 message, so that these values are readily available to the code-generating
269 (export 'compute-effective-method-body)
270 (defgeneric compute-effective-method-body (method codegen target)
272 "Generates the body of an effective method.
274 Writes the function body to the code generator. It can (obviously)
275 generate auxiliary functions if it needs to.
277 The arguments are as determined by agreement with the generic function
278 `compute-method-entry-functions'; usually this will be as specified by the
279 `sod-message-argument-tail', with any variable-argument tail reified to a
280 `va_list', and an additional argument `sod__obj' of type pointer-to-
281 ilayout. The code should deliver the result (if any) to the TARGET."))
283 (export 'simple-method-body)
284 (defgeneric simple-method-body (method codegen target)
286 "Generate the body of a simple effective method.
288 The function is invoked on an effective METHOD, with a CODEGEN to which it
289 should emit code delivering the method's value to TARGET."))
291 ;;; Additional instructions.
293 ;; HACK: use gensyms for the `class' and `expr' slots to avoid leaking the
294 ;; slot names, because `expr' is exported by our package, and `class' is
295 ;; actually from the `common-lisp' package.
296 (definst convert-to-ilayout (stream :export t)
297 (#1=#:class chain-head #2=#:expr)
298 (format stream "SOD_ILAYOUT(~@<~A, ~_~A, ~_~A~:>)"
299 #1# (sod-class-nickname chain-head) #2#))
303 (defvar-unbound *keyword-struct-disposition*
304 "The current state of the keyword structure.
306 This can be one of three values.
308 * `:local' -- the structure itself is in a local variable `sod__kw'.
309 This is used in the top-level effective method.
311 * `:pointer' -- the structure is pointed to by the local variable
312 `sod__kw'. This is used by delegation-chain trampolines.
314 * `:null' -- there is in fact no structure because none of the
315 applicable methods actually define any keywords.")
317 (defun keyword-access (name &optional suffix)
318 "Return an lvalue designating a named member of the keyword struct.
320 If a non-nil SUFFIX is provided, then the member is named NAMESUFFIX."
322 (format nil "~A~A~A~@[~A~]" *sod-keywords* op name suffix)))
323 (ecase *keyword-struct-disposition*
325 (:pointer (mem "->")))))
327 (let ((kw-addr (format nil "&~A" *sod-keywords*)))
328 (defun keyword-struct-pointer ()
329 "Return a pointer to the keyword structure."
330 (ecase *keyword-struct-disposition*
332 (:pointer *sod-keywords*)
333 (:null *null-pointer*))))
335 (export 'invoke-method)
336 (defun invoke-method (codegen target arguments-tail direct-method)
337 "Emit code to invoke DIRECT-METHOD, passing it ARGUMENTS-TAIL.
339 The code is generated in the context of CODEGEN, which can be any instance
340 of the `codegen' class -- it needn't be an instance of `method-codegen'.
341 The DIRECT-METHOD is called with the given ARGUMENTS-TAIL (a list of
342 argument expressions), preceded by a `me' argument of type pointer-to-
343 CLASS where CLASS is the class on which the method was defined.
345 If the message accepts a variable-length argument list then a copy of the
346 prevailing argument pointer is provided in place of the `:ellipsis'."
348 (let* ((message (sod-method-message direct-method))
349 (class (sod-method-class direct-method))
350 (function (sod-method-function-name direct-method))
351 (type (sod-method-type direct-method))
352 (keywordsp (keyword-message-p message))
353 (keywords (and keywordsp (c-function-keywords type)))
354 (arguments (append (list (format nil "&sod__obj->~A.~A"
356 (sod-class-chain-head class))
357 (sod-class-nickname class)))
359 (mapcar (lambda (arg)
360 (let ((name (argument-name arg))
361 (default (argument-default arg)))
366 (keyword-access name)
368 (keyword-access name))))
370 (cond ((varargs-message-p message)
371 (convert-stmts codegen target (c-type-subtype type)
373 (ensure-var codegen *sod-tmp-ap* c-type-va-list)
374 (deliver-call codegen :void "va_copy"
375 *sod-tmp-ap* *sod-ap*)
376 (apply #'deliver-call codegen var
378 (deliver-call codegen :void "va_end"
381 (let ((tag (direct-method-suppliedp-struct-tag direct-method)))
382 (with-temporary-var (codegen spvar (c-type (struct tag)))
383 (dolist (arg keywords)
384 (let ((name (argument-name arg)))
385 (deliver-expr codegen (format nil "~A.~A" spvar name)
386 (keyword-access name "__suppliedp"))))
387 (setf arguments (list* (car arguments) spvar
389 (apply #'deliver-call codegen target function arguments))))
391 (apply #'deliver-call codegen target function arguments)))))
393 (export 'ensure-ilayout-var)
394 (defun ensure-ilayout-var (codegen super)
395 "Define a variable `sod__obj' pointing to the class's ilayout structure.
397 CODEGEN is a `method-codegen'. The class in question is CODEGEN's class,
398 i.e., the target class for the effective method. SUPER is one of the
399 class's superclasses; it is assumed that `me' is a pointer to a SUPER
400 (i.e., to SUPER's ichain within the ilayout)."
402 (let* ((class (codegen-class codegen))
403 (super-head (sod-class-chain-head super)))
404 (ensure-var codegen "sod__obj"
405 (c-type (* (struct (ilayout-struct-tag class))))
406 (make-convert-to-ilayout-inst class super-head "me"))))
408 (export 'make-trampoline)
409 (defun make-trampoline (codegen super body)
410 "Construct a trampoline function and return its name.
412 CODEGEN is a `method-codegen'. SUPER is a superclass of the CODEGEN
413 class. We construct a new trampoline function (with an unimaginative
414 name) suitable for being passed to a direct method defined on SUPER as its
415 `next_method'. In particular, it will have a `me' argument whose type is
418 The code of the function is generated by BODY, which will be invoked with
419 a single argument which is the TARGET to which it should deliver its
422 The return value is the name of the generated function."
424 (let* ((message (codegen-message codegen))
425 (message-type (sod-message-type message))
426 (message-class (sod-message-class message))
427 (method (codegen-method codegen))
428 (return-type (c-type-subtype message-type))
429 (raw-args (sod-message-argument-tail message))
430 (arguments (cond ((varargs-message-p message)
431 (cons (make-argument *sod-ap* c-type-va-list)
433 ((keyword-message-p message)
434 (cons (make-argument *sod-key-pointer*
435 (c-type (* (void :const))))
437 (*keyword-struct-disposition* (if (effective-method-keywords method)
439 (codegen-push codegen)
440 (ensure-ilayout-var codegen super)
441 (when (keyword-message-p message)
442 (if (eq *keyword-struct-disposition* :null)
443 (deliver-call codegen :void "SOD__IGNORE" *sod-key-pointer*)
444 (let ((tag (effective-method-keyword-struct-tag method)))
445 (ensure-var codegen *sod-keywords*
446 (c-type (* (struct tag :const)))
447 *sod-key-pointer*))))
448 (funcall body (codegen-target codegen))
449 (codegen-pop-function codegen (temporary-function)
450 (c-type (fun (lisp return-type)
451 ("me" (* (class super)))
453 "Delegation-chain trampoline ~:_~
454 for `~A.~A' ~:_on `~A'."
455 (sod-class-nickname message-class)
456 (sod-message-name message)
457 (effective-method-class method))))
459 ;;;--------------------------------------------------------------------------
460 ;;; Method entry protocol.
462 (export 'effective-method-function-name)
463 (defgeneric effective-method-function-name (method)
465 "Returns the function name of an effective method."))
467 (export 'method-entry-function-name)
468 (defgeneric method-entry-function-name (method chain-head role)
470 "Returns the function name of a method entry.
472 The method entry is given as an effective method/chain-head/role triple,
473 rather than as a method entry object because we want the function name
474 before we've made the entry object."))
476 (export 'compute-method-entry-functions)
477 (defgeneric compute-method-entry-functions (method)
479 "Construct method entry functions.
481 Builds the effective method function (if there is one) and the necessary
482 method entries. Returns a list of functions (i.e., `function-inst'
483 objects) which need to be defined in the generated source code."))
485 ;;;--------------------------------------------------------------------------
486 ;;; Invoking direct methods.
488 (export 'invoke-delegation-chain)
489 (defun invoke-delegation-chain (codegen target basic-tail chain kernel)
490 "Invoke a chain of delegating methods.
492 CODEGEN is a `method-codegen'. BASIC-TAIL is a list of argument
493 expressions to provide to the methods. The result of the delegation chain
494 will be delivered to TARGET.
496 The CHAIN is a list of method objects (it's intended to be used with
497 `delegating-direct-method' objects). The behaviour is as follows. The
498 first method in the chain is invoked with the necessary arguments (see
499 below) including a `next_method' pointer. If KERNEL is nil and there are
500 no more methods in the chain then the `next_method' pointer will be null;
501 otherwise it will point to a `trampoline' function, whose behaviour is to
502 call the remaining methods on the chain as a delegation chain. The method
503 may choose to call this function with its arguments. It will finally
504 return a value, which will be delivered to the TARGET.
506 If the chain is empty, then the code generated by KERNEL (given a TARGET
507 argument) will be invoked. It is an error if both CHAIN and KERNEL are
510 (let* ((message (codegen-message codegen))
511 (argument-tail (if (varargs-message-p message)
512 (cons *sod-tmp-ap* basic-tail)
514 (labels ((next-trampoline (method chain)
515 (if (or kernel chain)
516 (make-trampoline codegen (sod-method-class method)
518 (invoke chain target)))
520 (invoke (chain target)
522 (funcall kernel target)
523 (let ((trampoline (next-trampoline (car chain)
525 (tail (if (keyword-message-p message)
526 (cons (keyword-struct-pointer)
529 (invoke-method codegen target
530 (cons trampoline tail)
532 (invoke chain target))))
534 ;;;----- That's all, folks --------------------------------------------------