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 'compute-sod-effective-method)
67 (defgeneric compute-sod-effective-method (message class)
69 "Return the effective method when a CLASS instance receives MESSAGE.
71 The default method constructs an instance of the message's chosen
72 `sod-message-effective-method-class', passing the MESSAGE, the CLASS and
73 the list of applicable methods as initargs to `make-instance'."))
75 (export 'compute-effective-methods)
76 (defgeneric compute-effective-methods (class)
78 "Return a list of all of the effective methods needed for CLASS.
80 The list needn't be in any particular order."))
82 (export '(method-entry method-entry-effective-method
83 method-entry-chain-head method-entry-chain-tail))
84 (defclass method-entry ()
85 ((%method :initarg :method :type effective-method
86 :reader method-entry-effective-method)
87 (chain-head :initarg :chain-head :type sod-class
88 :reader method-entry-chain-head)
89 (chain-tail :initarg :chain-tail :type sod-class
90 :reader method-entry-chain-tail)
91 (role :initarg :role :type (or keyword null) :reader method-entry-role))
93 "An entry point into an effective method.
95 Specifically, this is the entry point to the effective METHOD invoked via
96 the vtable for the chain headed by CHAIN-HEAD, and serving the given ROLE.
97 The CHAIN-TAIL is the most specific class on this chain; this is useful
98 because we can reuse the types of method entries from superclasses on
101 Each effective method may have several different method entries, because
102 an effective method can be called via vtables attached to different
103 chains, and such calls will pass instance pointers which point to
104 different `ichain' structures within the overall instance layout; it's the
105 job of the method entry to adjust the instance pointers correctly for the
106 rest of the effective method.
108 A vtable can contain more than one entry for the same message. Such
109 entries are distinguished by their roles. A message always has an entry
110 with the `nil role; in addition, a varargs message also has a `:valist'
111 role, which accepts a `va_list' argument in place of the variable argument
112 listNo other roles are currently defined, though they may be introduced by
115 The boundaries between a method entry and the effective method
116 is (intentionally) somewhat fuzzy. In extreme cases, the effective method
117 may not exist at all as a distinct entity in the output because its
118 content is duplicated in all of the method entry functions. This is left
119 up to the effective method protocol."))
121 (export 'make-method-entries)
122 (defgeneric make-method-entries (effective-method chain-head chain-tail)
124 "Return a list of `method-entry' objects for an EFFECTIVE-METHOD called
127 There is no default method for this function. (Maybe when the
128 effective-method/method-entry output protocol has settled down I'll know
129 what a sensible default action would be.)"))
131 ;;;--------------------------------------------------------------------------
132 ;;; Protocol for messages and direct-methods.
134 (export 'sod-message-argument-tail)
135 (defgeneric sod-message-argument-tail (message)
137 "Return the argument tail for the message, with invented argument names.
139 No `me' argument is prepended; any `:ellipsis' is left as it is."))
141 (export 'sod-method-function-type)
142 (defgeneric sod-method-function-type (method)
144 "Return the C function type for the direct method.
146 This is called during initialization of a direct method object, and the
149 A default method is provided (by `basic-direct-method') which simply
150 prepends an appropriate `me' argument to the user-provided argument list.
151 Fancy method classes may need to override this behaviour."))
153 (export 'sod-method-next-method-type)
154 (defgeneric sod-method-next-method-type (method)
156 "Return the C function type for the next-method trampoline.
158 This is called during initialization of a direct method object, and the
159 result is cached. It should return a function type, not a pointer type.
161 A default method is provided (by `delegating-direct-method') which should
162 do the right job. Very fancy subclasses might need to do something
165 (export 'sod-method-function-name)
166 (defgeneric sod-method-function-name (method)
168 "Return the C function name for the direct method."))
170 (export 'keyword-message-p)
171 (defun keyword-message-p (message)
172 "Answer whether the MESSAGE accepts a keyword arguments.
174 Dealing with keyword messages is rather fiddly, so this is useful to
176 (typep (sod-message-type message) 'c-keyword-function-type))
178 (export 'varargs-message-p)
179 (defun varargs-message-p (message)
180 "Answer whether the MESSAGE accepts a variable-length argument list.
182 We need to jump through some extra hoops in order to cope with varargs
183 messages, so this is useful to know."
184 (member :ellipsis (sod-message-argument-tail message)))
186 ;;;--------------------------------------------------------------------------
187 ;;; Protocol for effective methods and method entries.
189 (export 'method-entry-function-type)
190 (defgeneric method-entry-function-type (entry)
192 "Return the C function type for a method entry."))
194 (export 'method-entry-slot-name)
195 (defgeneric method-entry-slot-name (entry)
197 "Return the `vtmsgs' slot name for a method entry.
199 The default method indirects through `method-entry-slot-name-by-role'."))
201 (defgeneric method-entry-slot-name-by-role (entry role name)
202 (:documentation "Easier implementation for `method-entry-slot-name'.")
203 (:method ((entry method-entry) (role (eql nil)) name) name)
204 (:method ((entry method-entry) (role (eql :valist)) name)
205 (format nil "~A__v" name)))
207 (export 'effective-method-basic-argument-names)
208 (defgeneric effective-method-basic-argument-names (method)
210 "Return a list of argument names to be passed to direct methods.
212 The argument names are constructed from the message's arguments returned
213 by `sod-message-argument-tail', with any ellipsis replaced by an explicit
214 `va_list' argument. The basic arguments are the ones immediately derived
215 from the programmer's explicitly stated arguments; the `me' argument is
216 not included, and neither are more exotic arguments added as part of the
217 method delegation protocol."))
219 (export 'effective-method-live-p)
220 (defgeneric effective-method-live-p (method)
222 "Returns true if the effective METHOD is live.
224 An effective method is `live' if it should actually have proper method entry
225 functions associated with it and stored in the class vtable. The other
226 possibility is that the method is `dead', in which case the function
227 pointers in the vtable are left null."))
229 ;;;--------------------------------------------------------------------------
232 ;;; Enhanced code-generator class.
234 (export '(method-codegen codegen-message codegen-class
235 codegen-method codegen-target))
236 (defclass method-codegen (codegen)
237 ((message :initarg :message :type sod-message :reader codegen-message)
238 (%class :initarg :class :type sod-class :reader codegen-class)
239 (%method :initarg :method :type effective-method :reader codegen-method)
240 (target :initarg :target :reader codegen-target))
242 "Augments CODEGEN with additional state regarding an effective method.
244 We store the effective method, and also its target class and owning
245 message, so that these values are readily available to the code-generating
250 (export 'compute-effective-method-body)
251 (defgeneric compute-effective-method-body (method codegen target)
253 "Generates the body of an effective method.
255 Writes the function body to the code generator. It can (obviously)
256 generate auxiliary functions if it needs to.
258 The arguments are as determined by agreement with the generic function
259 `compute-method-entry-functions'; usually this will be as specified by the
260 `sod-message-argument-tail', with any variable-argument tail reified to a
261 `va_list', and an additional argument `sod__obj' of type pointer-to-
262 ilayout. The code should deliver the result (if any) to the TARGET."))
264 (export 'simple-method-body)
265 (defgeneric simple-method-body (method codegen target)
267 "Generate the body of a simple effective method.
269 The function is invoked on an effective METHOD, with a CODEGEN to which it
270 should emit code delivering the method's value to TARGET."))
272 ;;; Additional instructions.
274 ;; HACK: use gensyms for the `class' and `expr' slots to avoid leaking the
275 ;; slot names, because `expr' is exported by our package, and `class' is
276 ;; actually from the `common-lisp' package.
277 (definst convert-to-ilayout (stream :export t)
278 (#1=#:class chain-head #2=#:expr)
279 (format stream "SOD_ILAYOUT(~@<~A, ~_~A, ~_~A~:>)"
280 #1# (sod-class-nickname chain-head) #2#))
284 (defvar *keyword-struct-disposition* :unset
285 "The current state of the keyword structure.
287 This can be one of four values.
289 * `:unset' -- the top-level default, mostly because I can't leave it
290 unbound and write this documentation. Nothing that matters should see
293 * `:local' -- the structure itself is in a local variable `sod__kw'.
294 This is used in the top-level effective method.
296 * `:pointer' -- the structure is pointed to by the local variable
297 `sod__kw'. This is used by delegation-chain trampolines.
299 * `:null' -- there is in fact no structure because none of the
300 applicable methods actually define any keywords.")
302 (defun keyword-access (name &optional suffix)
303 "Return an lvalue designating a named member of the keyword struct.
305 If a non-nil SUFFIX is provided, then the member is named NAMESUFFIX."
307 (format nil "~A~A~A~@[~A~]" *sod-keywords* op name suffix)))
308 (ecase *keyword-struct-disposition*
310 (:pointer (mem "->")))))
312 (let ((kw-addr (format nil "&~A" *sod-keywords*)))
313 (defun keyword-struct-pointer ()
314 "Return a pointer to the keyword structure."
315 (ecase *keyword-struct-disposition*
317 (:pointer *sod-keywords*)
318 (:null *null-pointer*))))
320 (export 'invoke-method)
321 (defun invoke-method (codegen target arguments-tail direct-method)
322 "Emit code to invoke DIRECT-METHOD, passing it ARGUMENTS-TAIL.
324 The code is generated in the context of CODEGEN, which can be any instance
325 of the `codegen' class -- it needn't be an instance of `method-codegen'.
326 The DIRECT-METHOD is called with the given ARGUMENTS-TAIL (a list of
327 argument expressions), preceded by a `me' argument of type pointer-to-
328 CLASS where CLASS is the class on which the method was defined.
330 If the message accepts a variable-length argument list then a copy of the
331 prevailing argument pointer is provided in place of the `:ellipsis'."
333 (let* ((message (sod-method-message direct-method))
334 (class (sod-method-class direct-method))
335 (function (sod-method-function-name direct-method))
336 (type (sod-method-type direct-method))
337 (keywordsp (keyword-message-p message))
338 (keywords (and keywordsp (c-function-keywords type)))
339 (arguments (append (list (format nil "&sod__obj->~A.~A"
341 (sod-class-chain-head class))
342 (sod-class-nickname class)))
344 (mapcar (lambda (arg)
345 (let ((name (argument-name arg))
346 (default (argument-default arg)))
351 (keyword-access name)
353 (keyword-access name))))
355 (cond ((varargs-message-p message)
356 (convert-stmts codegen target (c-type-subtype type)
358 (ensure-var codegen *sod-tmp-ap* c-type-va-list)
359 (deliver-call codegen :void "va_copy"
360 *sod-tmp-ap* *sod-ap*)
361 (apply #'deliver-call codegen var
363 (deliver-call codegen :void "va_end"
366 (let ((tag (direct-method-suppliedp-struct-tag direct-method)))
367 (with-temporary-var (codegen spvar (c-type (struct tag)))
368 (dolist (arg keywords)
369 (let ((name (argument-name arg)))
370 (deliver-expr codegen (format nil "~A.~A" spvar name)
371 (keyword-access name "__suppliedp"))))
372 (setf arguments (list* (car arguments) spvar
374 (apply #'deliver-call codegen target function arguments))))
376 (apply #'deliver-call codegen target function arguments)))))
378 (export 'ensure-ilayout-var)
379 (defun ensure-ilayout-var (codegen super)
380 "Define a variable `sod__obj' pointing to the class's ilayout structure.
382 CODEGEN is a `method-codegen'. The class in question is CODEGEN's class,
383 i.e., the target class for the effective method. SUPER is one of the
384 class's superclasses; it is assumed that `me' is a pointer to a SUPER
385 (i.e., to SUPER's ichain within the ilayout)."
387 (let* ((class (codegen-class codegen))
388 (super-head (sod-class-chain-head super)))
389 (ensure-var codegen "sod__obj"
390 (c-type (* (struct (ilayout-struct-tag class))))
391 (make-convert-to-ilayout-inst class super-head "me"))))
393 (export 'make-trampoline)
394 (defun make-trampoline (codegen super body)
395 "Construct a trampoline function and return its name.
397 CODEGEN is a `method-codegen'. SUPER is a superclass of the CODEGEN
398 class. We construct a new trampoline function (with an unimaginative
399 name) suitable for being passed to a direct method defined on SUPER as its
400 `next_method'. In particular, it will have a `me' argument whose type is
403 The code of the function is generated by BODY, which will be invoked with
404 a single argument which is the TARGET to which it should deliver its
407 The return value is the name of the generated function."
409 (let* ((message (codegen-message codegen))
410 (message-type (sod-message-type message))
411 (message-class (sod-message-class message))
412 (method (codegen-method codegen))
413 (return-type (c-type-subtype message-type))
414 (raw-args (sod-message-argument-tail message))
415 (arguments (cond ((varargs-message-p message)
416 (cons (make-argument *sod-ap* c-type-va-list)
418 ((keyword-message-p message)
419 (cons (make-argument *sod-key-pointer*
420 (c-type (* (void :const))))
422 (*keyword-struct-disposition* t))
423 (codegen-push codegen)
424 (ensure-ilayout-var codegen super)
425 (when (and (keyword-message-p message)
426 (not (eq *keyword-struct-disposition* :null)))
427 (let ((tag (effective-method-keyword-struct-tag method)))
428 (ensure-var codegen *sod-keywords* (c-type (* (struct tag :const)))
430 (funcall body (codegen-target codegen))
431 (codegen-pop-function codegen (temporary-function)
432 (c-type (fun (lisp return-type)
433 ("me" (* (class super)))
435 "Delegation-chain trampoline ~:_~
436 for `~A.~A' ~:_on `~A'."
437 (sod-class-nickname message-class)
438 (sod-message-name message)
439 (effective-method-class method))))
441 ;;;--------------------------------------------------------------------------
442 ;;; Method entry protocol.
444 (export 'effective-method-function-name)
445 (defgeneric effective-method-function-name (method)
447 "Returns the function name of an effective method."))
449 (export 'method-entry-function-name)
450 (defgeneric method-entry-function-name (method chain-head role)
452 "Returns the function name of a method entry.
454 The method entry is given as an effective method/chain-head/role triple,
455 rather than as a method entry object because we want the function name
456 before we've made the entry object."))
458 (export 'compute-method-entry-functions)
459 (defgeneric compute-method-entry-functions (method)
461 "Construct method entry functions.
463 Builds the effective method function (if there is one) and the necessary
464 method entries. Returns a list of functions (i.e., `function-inst'
465 objects) which need to be defined in the generated source code."))
467 ;;;--------------------------------------------------------------------------
468 ;;; Invoking direct methods.
470 (export 'invoke-delegation-chain)
471 (defun invoke-delegation-chain (codegen target basic-tail chain kernel)
472 "Invoke a chain of delegating methods.
474 CODEGEN is a `method-codegen'. BASIC-TAIL is a list of argument
475 expressions to provide to the methods. The result of the delegation chain
476 will be delivered to TARGET.
478 The CHAIN is a list of method objects (it's intended to be used with
479 `delegating-direct-method' objects). The behaviour is as follows. The
480 first method in the chain is invoked with the necessary arguments (see
481 below) including a `next_method' pointer. If KERNEL is nil and there are
482 no more methods in the chain then the `next_method' pointer will be null;
483 otherwise it will point to a `trampoline' function, whose behaviour is to
484 call the remaining methods on the chain as a delegation chain. The method
485 may choose to call this function with its arguments. It will finally
486 return a value, which will be delivered to the TARGET.
488 If the chain is empty, then the code generated by KERNEL (given a TARGET
489 argument) will be invoked. It is an error if both CHAIN and KERNEL are
492 (let* ((message (codegen-message codegen))
493 (argument-tail (cond ((varargs-message-p message)
494 (cons *sod-tmp-ap* basic-tail))
495 ((keyword-message-p message)
496 (cons (keyword-struct-pointer) basic-tail))
498 (labels ((next-trampoline (method chain)
499 (if (or kernel chain)
500 (make-trampoline codegen (sod-method-class method)
502 (invoke chain target)))
504 (invoke (chain target)
506 (funcall kernel target)
507 (let ((trampoline (next-trampoline (car chain)
509 (invoke-method codegen target
510 (cons trampoline argument-tail)
512 (invoke chain target))))
514 ;;;----- That's all, folks --------------------------------------------------