1 @node Beyond the ANSI Standard
2 @comment node-name, next, previous, up
3 @chapter Beyond the ANSI Standard
5 SBCL is derived from CMUCL, which implements many extensions to the
6 ANSI standard. SBCL doesn't support as many extensions as CMUCL, but
7 it still has quite a few. @xref{Contributed Modules}.
10 * Garbage Collection::
11 * Metaobject Protocol::
13 * Customization Hooks for Users::
14 * Tools To Help Developers::
15 * Resolution of Name Conflicts::
16 * Hash Table Extensions::
17 * Miscellaneous Extensions::
22 @node Garbage Collection
23 @comment node-name, next, previous, up
24 @section Garbage Collection
25 @cindex Garbage collection
27 SBCL provides additional garbage collection functionality not
30 @include var-sb-ext-star-after-gc-hooks-star.texinfo
31 @include fun-sb-ext-gc.texinfo
33 @subsection Finalization
36 Finalization allows code to be executed after an object has been
37 garbage collected. This is useful for example for releasing foreign
38 memory associated with a Lisp object.
40 @include fun-sb-ext-finalize.texinfo
41 @include fun-sb-ext-cancel-finalization.texinfo
43 @subsection Weak Pointers
46 Weak pointers allow references to objects to be maintained without
47 keeping them from being garbage collected: useful for building caches
50 Hash tables can also have weak keys and values: @pxref{Hash Table
53 @include fun-sb-ext-make-weak-pointer.texinfo
54 @include fun-sb-ext-weak-pointer-value.texinfo
56 @subsection Introspection and Tuning
58 @include var-sb-ext-star-gc-run-time-star.texinfo
59 @include fun-sb-ext-bytes-consed-between-gcs.texinfo
60 @include fun-sb-ext-generation-average-age.texinfo
61 @include fun-sb-ext-generation-bytes-allocated.texinfo
62 @include fun-sb-ext-generation-bytes-consed-between-gcs.texinfo
63 @include fun-sb-ext-generation-minimum-age-before-gc.texinfo
64 @include fun-sb-ext-generation-number-of-gcs-before-promotion.texinfo
65 @include fun-sb-ext-generation-number-of-gcs.texinfo
66 @include fun-sb-ext-get-bytes-consed.texinfo
68 @node Metaobject Protocol
69 @comment node-name, next, previous, up
70 @section Metaobject Protocol
72 @subsection AMOP Compatibility of Metaobject Protocol
74 SBCL supports a metaobject protocol which is intended to be compatible
75 with AMOP; present exceptions to this (as distinct from current bugs)
81 @findex @sbmop{compute-effective-method}
82 @code{compute-effective-method} only returns one value, not two.
84 There is no record of what the second return value was meant to
85 indicate, and apparently no clients for it.
88 @tindex @cl{generic-function}
89 @tindex @cl{standard-generic-function}
90 @tindex @sbmop{funcallable-standard-object}
91 @tindex @cl{standard-object}
93 The direct superclasses of @code{sb-mop:funcallable-standard-object} are
94 @code{(function standard-object)}, not @code{(standard-object function)}.
96 This is to ensure that the @code{standard-object} class is the last of
97 the standardized classes before @code{t} appearing in the class
98 precedence list of @code{generic-function} and
99 @code{standard-generic-function}, as required by section 1.4.4.5 of the
103 @findex @cl{ensure-generic-function}
104 @findex @sbmop{generic-function-declarations}
105 the arguments @code{:declare} and @code{:declarations} to
106 @code{ensure-generic-function} are both accepted, with the leftmost
107 argument defining the declarations to be stored and returned by
108 @code{generic-function-declarations}.
110 Where AMOP specifies @code{:declarations} as the keyword argument to
111 @code{ensure-generic-function}, the Common Lisp standard specifies
112 @code{:declare}. Portable code should use @code{:declare}.
115 @findex @sbmop{validate-superclass}
116 @findex @sbmop{finalize-inheritance}
117 @tindex @cl{standard-class}
118 @tindex @sbmop{funcallable-standard-class}
119 @tindex @cl{function}
120 @findex @sbmop{class-prototype}
121 although SBCL obeys the requirement in AMOP that
122 @code{validate-superclass} should treat @code{standard-class} and
123 @code{funcallable-standard-class} as compatible metaclasses, we
124 impose an additional requirement at class finalization time: a class
125 of metaclass @code{funcallable-standard-class} must have
126 @code{function} in its superclasses, and a class of metaclass
127 @code{standard-class} must not.
130 @findex @cl{class-of}
131 @findex @cl{subtypep}
132 After a class has been finalized, it is associated with a class
133 prototype which is accessible by a standard mop function
134 @code{sb-mop:class-prototype}. The user can then ask whether this
135 object is a @code{function} or not in several different ways: whether it
136 is a function according to @code{typep}; whether its @code{class-of} is
137 @code{subtypep} @code{function}, or whether @code{function} appears in
138 the superclasses of the class. The additional consistency requirement
139 comes from the desire to make all of these answers the same.
141 The following class definitions are bad, and will lead to errors
142 either immediately or if an instance is created:
144 (defclass bad-object (funcallable-standard-object)
146 (:metaclass standard-class))
149 (defclass bad-funcallable-object (standard-object)
151 (:metaclass funcallable-standard-class))
153 The following definition is acceptable:
156 ((slot :initarg slot)))
157 (defclass funcallable-object (funcallable-standard-object mixin)
159 (:metaclass funcallable-standard-class))
161 and leads to a class whose instances are funcallable and have one slot.
163 @tindex @sbmop{funcallable-standard-object}
164 Note that this requirement also applies to the class
165 @code{sb-mop:funcallable-standard-object}, which has metaclass
166 @code{sb-mop:funcallable-standard-class} rather than
167 @code{standard-class} as AMOP specifies.
170 the requirement that ``No portable class @math{C_p} may inherit, by
171 virtue of being a direct or indirect subclass of a specified class, any
172 slot for which the name is a symbol accessible in the
173 @code{common-lisp-user} package or exported by any package defined in
174 the ANSI Common Lisp standard.'' is interpreted to mean that the
175 standardized classes themselves should not have slots named by external
176 symbols of public packages.
178 The rationale behind the restriction is likely to be similar to the ANSI
179 Common Lisp restriction on defining functions, variables and types named
180 by symbols in the Common Lisp package: preventing two independent pieces
181 of software from colliding with each other.
184 @findex @sbmop{slot-value-using-class}
185 @findex @setf{@sbmop{slot-value-using-class}}
186 @findex @sbmop{slot-boundp-using-class}
187 specializations of the @code{new-value} argument to @code{(setf
188 sb-mop:slot-value-using-class)} are not allowed: all user-defined
189 methods must have a specializer of the class @code{t}.
191 This prohibition is motivated by a separation of layers: the
192 @code{slot-value-using-class} family of functions is intended for use in
193 implementing different and new slot allocation strategies, rather than
194 in performing application-level dispatching. Additionally, with this
195 requirement, there is a one-to-one mapping between metaclass, class and
196 slot-definition-class tuples and effective methods of @code{(setf
197 slot-value-using-class)}, which permits optimization of @code{(setf
198 slot-value-using-class)}'s discriminating function in the same manner as
199 for @code{slot-value-using-class} and @code{slot-boundp-using-class}.
201 Note that application code may specialize on the @code{new-value}
202 argument of slot accessors.
205 @findex @cl{defclass}
206 @findex @sbmop{ensure-class}
207 @findex @sbmop{ensure-class-using-class}
208 @findex @cl{find-class}
209 @findex @cl{class-name}
210 the class named by the @code{name} argument to @code{ensure-class}, if
211 any, is only redefined if it is the proper name of that class;
212 otherwise, a new class is created.
214 This is consistent with the description of @code{ensure-class} in AMOP
215 as the functional version of @code{defclass}, which has this behaviour;
216 however, it is not consistent with the weaker requirement in AMOP, which
217 states that any class found by @code{find-class}, no matter what its
218 @code{class-name}, is redefined.
222 @subsection Metaobject Protocol Extensions
224 In addition, SBCL supports extensions to the Metaobject protocol from
225 AMOP; at present, they are:
230 @findex @cl{defmethod}
231 @findex @cl{find-class}
232 @findex @sbmop{intern-eql-specializer}
233 @findex @sbpcl{make-method-specializers-form}
234 @findex @sbmop{make-method-lambda}
235 compile-time support for generating specializer metaobjects from
236 specializer names in @code{defmethod} forms is provided by the
237 @code{make-method-specializers-form} function, which returns a form
238 which, when evaluated in the lexical environment of the
239 @code{defmethod}, returns a list of specializer metaobjects. This
240 operator suffers from similar restrictions to those affecting
241 @code{make-method-lambda}, namely that the generic function must be
242 defined when the @code{defmethod} form is expanded, so that the
243 correct method of @code{make-method-specializers-form} is invoked.
244 The system-provided method on @code{make-method-specializers-form}
245 generates a call to @code{find-class} for each symbol specializer
246 name, and a call to @code{intern-eql-specializer} for each @code{(eql
247 @var{x})} specializer name.
250 @findex @cl{find-method}
251 @findex @sbpcl{parse-specializer-using-class}
252 @findex @sbpcl{unparse-specializer-using-class}
253 run-time support for converting between specializer names and
254 specializer metaobjects, mostly for the purposes of
255 @code{find-method}, is provided by
256 @code{parse-specializer-using-class} and
257 @code{unparse-specializer-using-class}, which dispatch on their first
258 argument, the generic function associated with a method with the given
259 specializer. The system-provided methods on those methods convert
260 between classes and proper names and between lists of the form
261 @code{(eql @var{x})} and interned eql specializer objects.
264 @vindex @sbpcl{+slot-unbound+}
265 @findex @sbmop{standard-instance-access}
266 @findex @sbmop{funcallable-standard-instance-access}
267 distinguising unbound instance allocated slots from bound ones when
268 using @code{standard-instance-access} and
269 @code{funcallable-standard-instance-access} is possible by comparison
270 to the constant @code{+slot-unbound+}.
274 @node Support For Unix
275 @comment node-name, next, previous, up
276 @section Support For Unix
279 * Command-line arguments::
280 * Querying the process environment::
281 * Running external programs::
284 @node Command-line arguments
285 @subsection Command-line arguments
286 @vindex @sbext{@earmuffs{posix-argv}}
288 The UNIX command line can be read from the variable
289 @code{sb-ext:*posix-argv*}.
291 @node Querying the process environment
292 @subsection Querying the process environment
294 The UNIX environment can be queried with the
295 @code{sb-ext:posix-getenv} function.
297 @include fun-sb-ext-posix-getenv.texinfo
299 @node Running external programs
300 @subsection Running external programs
302 External programs can be run with @code{sb-ext:run-program}.
303 @footnote{In SBCL versions prior to 1.0.13, @code{sb-ext:run-program}
304 searched for executables in a manner somewhat incompatible with other
305 languages. As of this version, SBCL uses the system library routine
306 @code{execvp(3)}, and no longer contains the function,
307 @code{find-executable-in-search-path}, which implemented the old
308 search. Users who need this function may find it
309 in @file{run-program.lisp} versions 1.67 and earlier in SBCL's CVS
311 @url{http://sbcl.cvs.sourceforge.net/sbcl/sbcl/src/code/run-program.lisp?view=log}. However,
312 we caution such users that this search routine finds executables that
313 system library routines do not.}
315 @include fun-sb-ext-run-program.texinfo
317 When @code{sb-ext:run-program} is called with @code{wait} equal to
318 NIL, an instance of class @var{sb-ext:process} is returned. The
319 following functions are available for use with processes:
321 @include fun-sb-ext-process-p.texinfo
323 @include fun-sb-ext-process-input.texinfo
325 @include fun-sb-ext-process-output.texinfo
327 @include fun-sb-ext-process-error.texinfo
329 @include fun-sb-ext-process-alive-p.texinfo
331 @include fun-sb-ext-process-status.texinfo
333 @include fun-sb-ext-process-wait.texinfo
335 @include fun-sb-ext-process-exit-code.texinfo
337 @include fun-sb-ext-process-core-dumped.texinfo
339 @include fun-sb-ext-process-close.texinfo
341 @include fun-sb-ext-process-kill.texinfo
343 @node Customization Hooks for Users
344 @comment node-name, next, previous, up
345 @section Customization Hooks for Users
347 The toplevel repl prompt may be customized, and the function
348 that reads user input may be replaced completely.
349 @c <!-- FIXME but I don't currently remember how -->
351 The behaviour of @code{require} when called with only one argument is
352 implementation-defined. In SBCL, @code{require} behaves in the
355 @include fun-common-lisp-require.texinfo
356 @include var-sb-ext-star-module-provider-functions-star.texinfo
358 Although SBCL does not provide a resident editor, the @code{ed}
359 function can be customized to hook into user-provided editing
360 mechanisms as follows:
362 @include fun-common-lisp-ed.texinfo
363 @include var-sb-ext-star-ed-functions-star.texinfo
365 Conditions of type @code{warning} and @code{style-warning} are
366 sometimes signaled at runtime, especially during execution of Common
367 Lisp defining forms such as @code{defun}, @code{defmethod}, etc. To
368 muffle these warnings at runtime, SBCL provides a variable
369 @code{sb-ext:*muffled-warnings*}:
371 @include var-sb-ext-star-muffled-warnings-star.texinfo
373 @node Tools To Help Developers
374 @comment node-name, next, previous, up
375 @section Tools To Help Developers
379 SBCL provides a profiler and other extensions to the ANSI @code{trace}
380 facility. For more information, see @ref{Macro common-lisp:trace}.
382 The debugger supports a number of options. Its documentation is
383 accessed by typing @kbd{help} at the debugger prompt. @xref{Debugger}.
385 Documentation for @code{inspect} is accessed by typing @kbd{help} at
386 the @code{inspect} prompt.
388 @node Resolution of Name Conflicts
389 @section Resolution of Name Conflicts
390 @tindex @sbext{name-conflict}
391 @findex @sbext{name-conflict-symbols}
393 The ANSI standard (section 11.1.1.2.5) requires that name conflicts in
394 packages be resolvable in favour of any of the conflicting symbols. In
395 the interactive debugger, this is achieved by prompting for the symbol
396 in whose favour the conflict should be resolved; for programmatic use,
397 the @code{sb-ext:resolve-conflict} restart should be invoked with one
398 argument, which should be a member of the list returned by the condition
399 accessor @code{sb-ext:name-conflict-symbols}.
401 @node Hash Table Extensions
402 @comment node-name, next, previous, up
403 @section Hash Table Extensions
406 Hash table extensions supported by SBCL are all controlled by keyword
407 arguments to @code{make-hash-table}.
409 @include fun-common-lisp-make-hash-table.texinfo
411 @include macro-sb-ext-define-hash-table-test.texinfo
413 @include macro-sb-ext-with-locked-hash-table.texinfo
415 @include fun-sb-ext-hash-table-synchronized-p.texinfo
417 @include fun-sb-ext-hash-table-weakness.texinfo
419 @node Miscellaneous Extensions
420 @comment node-name, next, previous, up
421 @section Miscellaneous Extensions
423 @include fun-sb-ext-array-storage-vector.texinfo
424 @include fun-sb-ext-delete-directory.texinfo
425 @include fun-sb-ext-get-time-of-day.texinfo
426 @include fun-sb-ext-seed-random-state.texinfo
428 @node Stale Extensions
429 @comment node-name, next, previous, up
430 @section Stale Extensions
432 SBCL has inherited from CMUCL various hooks to allow the user to
433 tweak and monitor the garbage collection process. These are somewhat
434 stale code, and their interface might need to be cleaned up. If you
435 have urgent need of them, look at the code in @file{src/code/gc.lisp}
436 and bring it up on the developers' mailing list.
438 SBCL has various hooks inherited from CMUCL, like
439 @code{sb-ext:float-denormalized-p}, to allow a program to take
440 advantage of IEEE floating point arithmetic properties which aren't
441 conveniently or efficiently expressible using the ANSI standard. These
442 look good, and their interface looks good, but IEEE support is
443 slightly broken due to a stupid decision to remove some support for
444 infinities (because it wasn't in the ANSI spec and it didn't occur to
445 me that it was in the IEEE spec). If you need this stuff, take a look
446 at the code and bring it up on the developers' mailing
450 @node Efficiency Hacks
451 @comment node-name, next, previous, up
452 @section Efficiency Hacks
454 The @code{sb-ext:purify} function causes SBCL first to collect all
455 garbage, then to mark all uncollected objects as permanent, never again
456 attempting to collect them as garbage. This can cause a large increase
457 in efficiency when using a primitive garbage collector, or a more
458 moderate increase in efficiency when using a more sophisticated garbage
459 collector which is well suited to the program's memory usage pattern. It
460 also allows permanent code to be frozen at fixed addresses, a
461 precondition for using copy-on-write to share code between multiple Lisp
462 processes. This is less important with modern generational garbage
463 collectors, but not all SBCL platforms use such a garbage collector.
465 @include fun-sb-ext-purify.texinfo
467 The @code{sb-ext:truly-the} special form declares the type of the
468 result of the operations, producing its argument; the declaration is
469 not checked. In short: don't use it.
471 @include special-operator-sb-ext-truly-the.texinfo
473 The @code{sb-ext:freeze-type} declaration declares that a
474 type will never change, which can make type testing
475 (@code{typep}, etc.) more efficient for structure types.