@comment node-name, next, previous, up
@chapter Beyond the ANSI Standard
-SBCL is mostly an implementation of the ANSI standard for
-Common Lisp. However, there's some important behavior which extends
-or clarifies the standard, and various behavior which outright
-violates the standard.
-
+SBCL is derived from CMUCL, which implements many extensions to the
+ANSI standard. SBCL doesn't support as many extensions as CMUCL, but
+it still has quite a few. @xref{Contributed Modules}.
@menu
-* Non-Conformance With The ANSI Standard::
-* Idiosyncrasies::
-* Extensions::
+* Reader Extensions::
+* Package-Local Nicknames::
+* Package Variance::
+* Garbage Collection::
+* Metaobject Protocol::
+* Extensible Sequences::
+* Support For Unix::
+* Customization Hooks for Users::
+* Tools To Help Developers::
+* Resolution of Name Conflicts::
+* Hash Table Extensions::
+* Random Number Generation::
+* Miscellaneous Extensions::
+* Stale Extensions::
+* Efficiency Hacks::
@end menu
-@node Non-Conformance With The ANSI Standard
+@node Reader Extensions
@comment node-name, next, previous, up
-@section Non-Conformance With The ANSI Standard
+@section Reader Extensions
+@cindex Reader Extensions
-Essentially every type of non-conformance is considered a bug. (The
-exceptions involve internal inconsistencies in the standard.) In SBCL
-0.7.6, the master record of known bugs is in the @file{BUGS} file in
-the distribution. Some highlight information about bugs may also be
-found in the manual page. The recommended way to report bugs is
-through the sbcl-help or sbcl-devel mailing lists. For mailing list
-addresses, @xref{More SBCL Information}.
+SBCL supports extended package prefix syntax, which allows specifying
+an alternate package instead of @code{*package*} for the reader to use
+as the default package for interning symbols:
+@lisp
+<package-name>::<form-with-interning-into-package>
+@end lisp
+
+Example:
-@node Idiosyncrasies
-@comment node-name, next, previous, up
-@section Idiosyncrasies
-
-The information in this section describes some of the ways that SBCL
-deals with choices that the ANSI standard leaves to the
-implementation.
-
-Declarations are generally treated as assertions. This general
-principle, and its implications, and the bugs which still keep the
-compiler from quite satisfying this principle, are discussed in
-@ref{Compiler}.
-
-SBCL is essentially a compiler-only implementation of Common
-Lisp. That is, for all but a few special cases, @code{eval} creates a
-lambda expression, calls @code{compile} on the lambda expression to
-create a compiled function, and then calls @code{funcall} on the
-resulting function object. This is explicitly allowed by the ANSI
-standard, but leads to some oddities, e.g. collapsing @code{functionp}
-and @code{compiled-function-p} into the same predicate.
-
-@findex defconstant
-SBCL is quite strict about ANSI's definition of
-@code{defconstant}. ANSI says that doing @code{defconstant} of the
-same symbol more than once is undefined unless the new value is
-@code{eql} to the old value. Conforming to this specification is a
-nuisance when the ``constant'' value is only constant under some
-weaker test like @code{string=} or @code{equal}. It's especially
-annoying because, in SBCL, @code{defconstant} takes effect not only at
-load time but also at compile time, so that just compiling and loading
-reasonable code like
@lisp
-(defconstant +foobyte+ '(1 4))
+ 'foo::(bar quux zot) == '(foo::bar foo::quux foo::zot)
@end lisp
-runs into this undefined behavior. Many implementations of Common Lisp
-try to help the programmer around this annoyance by silently accepting
-the undefined code and trying to do what the programmer probably
-meant. SBCL instead treats the undefined behavior as an error. Often
-such code can be rewritten in portable ANSI Common Lisp which has the
-desired behavior. E.g., the code above can be given an exactly
-defined meaning by replacing @code{defconstant} either with
-@code{defparameter} or with a customized macro which does the right
-thing, possibly along the lines of the @code{defconstant-eqx} macro
-used internally in the implementation of SBCL itself. In
-circumstances where this is not appropriate, the programmer can handle
-the condition type @code{sb-ext:defconstant-uneql}, and choose either
-the @command{continue} or @command{abort} restart as appropriate.
-
-SBCL gives style warnings about various kinds of perfectly legal code,
-e.g.
+
+Doesn't alter @code{*package*}: if @code{foo::bar} would cause a
+read-time package lock violation, so does @code{foo::(bar)}.
+
+@node Package-Local Nicknames
+@comment node-name, next, previous, up
+@section Package-Local Nicknames
+@cindex Package-Local Nicknames
+
+SBCL allows giving packages local nicknames: they allow short and
+easy-to-use names to be used without fear of name conflict associated
+with normal nicknames.
+
+A local nickname is valid only when inside the package for which it
+has been specified. Different packages can use same local nickname for
+different global names, or different local nickname for same global
+name.
+
+Symbol @code{:package-local-nicknames} in @code{*features*} denotes the
+support for this feature.
+
+@findex @cl{defpackage}
+@defmac @cl{defpackage} name [[option]]* @result{} package
+
+Options are extended to include
@itemize
-
-@item
-@code{defmethod} without a preceding @code{defgeneric};
-
@item
-multiple @code{defun}s of the same symbol in different units;
-
-@item
-special variables not named in the conventional @code{*foo*} style,
-and lexical variables unconventionally named in the @code{*foo*} style
+@code{:local-nicknames (@var{local-nickname} @var{actual-package-name})*}
+The package has the specified local nicknames for the corresponding
+actual packages.
@end itemize
-This causes friction with people who point out that other ways of
-organizing code (especially avoiding the use of @code{defgeneric}) are
-just as aesthetically stylish. However, these warnings should be read
-not as ``warning, bad aesthetics detected, you have no style'' but
-``warning, this style keeps the compiler from understanding the code
-as well as you might like.'' That is, unless the compiler warns about
-such conditions, there's no way for the compiler to warn about some
-programming errors which would otherwise be easy to overlook. (Related
-bug: The warning about multiple @code{defun}s is pointlessly annoying
-when you compile and then load a function containing @code{defun}
-wrapped in @code{eval-when}, and ideally should be suppressed in that
-case, but still isn't as of SBCL 0.7.6.)
-
-
-@node Extensions
+Example:
+
+@lisp
+(defpackage :bar (:intern "X"))
+(defpackage :foo (:intern "X"))
+(defpackage :quux (:use :cl) (:local-nicknames (:bar :foo) (:foo :bar)))
+(find-symbol "X" :foo) ; => FOO::X
+(find-symbol "X" :bar) ; => BAR::X
+(let ((*package* (find-package :quux)))
+ (find-symbol "X" :foo)) ; => BAR::X
+(let ((*package* (find-package :quux)))
+ (find-symbol "X" :bar)) ; => FOO::X
+@end lisp
+@end defmac
+
+@include fun-sb-ext-package-local-nicknames.texinfo
+@include fun-sb-ext-package-locally-nicknamed-by-list.texinfo
+@include fun-sb-ext-add-package-local-nickname.texinfo
+@include fun-sb-ext-remove-package-local-nickname.texinfo
+
+@node Package Variance
@comment node-name, next, previous, up
-@section Extensions
+@section Package Variance
-SBCL is derived from CMUCL, which implements many extensions to the
-ANSI standard. SBCL doesn't support as many extensions as CMUCL, but
-it still has quite a few. @xref{Contributed Modules}.
+Common Lisp standard specifies that ``If the new definition is at
+variance with the current state of that package, the consequences are
+undefined;'' SBCL by default signals a full warning and retains as
+much of the package state as possible.
+This can be adjusted using @code{sb-ext:*on-package-variance*}:
-@menu
-* Things Which Might Be In The Next ANSI Standard::
-* Threading::
-* Support For Unix::
-* Customization Hooks for Users::
-* Tools To Help Developers::
-* Interface To Low-Level SBCL Implementation::
-* Stale Extensions::
-* Efficiency Hacks::
-@end menu
+@include var-sb-ext-star-on-package-variance-star.texinfo
-@node Things Which Might Be In The Next ANSI Standard
+@node Garbage Collection
@comment node-name, next, previous, up
-@subsection Things Which Might Be In The Next ANSI Standard
-
-SBCL provides extensive support for calling external C code,
-@ref{Foreign Function Interface}.
+@section Garbage Collection
+@cindex Garbage collection
SBCL provides additional garbage collection functionality not
-specified by ANSI. Weak pointers allow references to objects to be
-maintained without keeping them from being GCed (garbage
-collected). And ``finalization'' hooks are available to cause code to
-be executed when an object has been GCed.
-@c <!-- FIXME: Actually documenting these would be good.:-| -->
-
-SBCL supports @dfn{Gray streams}, user-overloadable CLOS classes whose
-instances can be used as Lisp streams (e.g. passed as the first
-argument to @code{format}). Additionally, the bundled contrib module
-@dfn{sb-simple-streams} implements a subset of the Franz Allegro
-simple-streams proposal.
-
-SBCL supports a MetaObject Protocol which is intended to be compatible
+specified by ANSI.
+
+@include var-sb-ext-star-after-gc-hooks-star.texinfo
+@include fun-sb-ext-gc.texinfo
+
+@subsection Finalization
+@cindex Finalization
+
+Finalization allows code to be executed after an object has been
+garbage collected. This is useful for example for releasing foreign
+memory associated with a Lisp object.
+
+@include fun-sb-ext-finalize.texinfo
+@include fun-sb-ext-cancel-finalization.texinfo
+
+@subsection Weak Pointers
+@cindex Weak pointers
+
+Weak pointers allow references to objects to be maintained without
+keeping them from being garbage collected: useful for building caches
+among other things.
+
+Hash tables can also have weak keys and values: @pxref{Hash Table
+Extensions}.
+
+@include fun-sb-ext-make-weak-pointer.texinfo
+@include fun-sb-ext-weak-pointer-value.texinfo
+
+@subsection Introspection and Tuning
+
+@include var-sb-ext-star-gc-run-time-star.texinfo
+@include fun-sb-ext-bytes-consed-between-gcs.texinfo
+@include fun-sb-ext-dynamic-space-size.texinfo
+@include fun-sb-ext-get-bytes-consed.texinfo
+@include fun-sb-ext-gc-logfile.texinfo
+@include fun-sb-ext-generation-average-age.texinfo
+@include fun-sb-ext-generation-bytes-allocated.texinfo
+@include fun-sb-ext-generation-bytes-consed-between-gcs.texinfo
+@include fun-sb-ext-generation-minimum-age-before-gc.texinfo
+@include fun-sb-ext-generation-number-of-gcs-before-promotion.texinfo
+@include fun-sb-ext-generation-number-of-gcs.texinfo
+
+@node Metaobject Protocol
+@comment node-name, next, previous, up
+@section Metaobject Protocol
+
+@subsection AMOP Compatibility of Metaobject Protocol
+
+SBCL supports a metaobject protocol which is intended to be compatible
with AMOP; present exceptions to this (as distinct from current bugs)
are:
@itemize
-
+
@item
-the abstract @code{metaobject} class is not present in the class
-hierarchy;
-
+@findex @sbmop{compute-effective-method}
+@code{compute-effective-method} only returns one value, not two.
+
+There is no record of what the second return value was meant to
+indicate, and apparently no clients for it.
+
@item
-the @code{standard-object} and @code{funcallable-standard-object}
-classes are disjoint;
-
+@tindex @cl{generic-function}
+@tindex @cl{standard-generic-function}
+@tindex @sbmop{funcallable-standard-object}
+@tindex @cl{standard-object}
+@tindex @cl{function}
+The direct superclasses of @code{sb-mop:funcallable-standard-object} are
+@code{(function standard-object)}, not @code{(standard-object function)}.
+
+This is to ensure that the @code{standard-object} class is the last of
+the standardized classes before @code{t} appearing in the class
+precedence list of @code{generic-function} and
+@code{standard-generic-function}, as required by section 1.4.4.5 of the
+ANSI specification.
+
@item
-@code{compute-effective-method} only returns one value, not two;
-
+@findex @cl{ensure-generic-function}
+@findex @sbmop{generic-function-declarations}
+the arguments @code{:declare} and @code{:declarations} to
+@code{ensure-generic-function} are both accepted, with the leftmost
+argument defining the declarations to be stored and returned by
+@code{generic-function-declarations}.
+
+Where AMOP specifies @code{:declarations} as the keyword argument to
+@code{ensure-generic-function}, the Common Lisp standard specifies
+@code{:declare}. Portable code should use @code{:declare}.
+
@item
-the system-supplied @code{:around} method for @code{compute-slots}
-specialized on @code{funcallable-standard-class} does not respect the
-requested order from a user-supplied primary method.
+@findex @sbmop{validate-superclass}
+@findex @sbmop{finalize-inheritance}
+@tindex @cl{standard-class}
+@tindex @sbmop{funcallable-standard-class}
+@tindex @cl{function}
+@findex @sbmop{class-prototype}
+although SBCL obeys the requirement in AMOP that
+@code{validate-superclass} should treat @code{standard-class} and
+@code{funcallable-standard-class} as compatible metaclasses, we
+impose an additional requirement at class finalization time: a class
+of metaclass @code{funcallable-standard-class} must have
+@code{function} in its superclasses, and a class of metaclass
+@code{standard-class} must not.
+
+@findex @cl{typep}
+@findex @cl{class-of}
+@findex @cl{subtypep}
+After a class has been finalized, it is associated with a class
+prototype which is accessible by a standard mop function
+@code{sb-mop:class-prototype}. The user can then ask whether this
+object is a @code{function} or not in several different ways: whether it
+is a function according to @code{typep}; whether its @code{class-of} is
+@code{subtypep} @code{function}, or whether @code{function} appears in
+the superclasses of the class. The additional consistency requirement
+comes from the desire to make all of these answers the same.
+
+The following class definitions are bad, and will lead to errors
+either immediately or if an instance is created:
+@lisp
+(defclass bad-object (funcallable-standard-object)
+ ()
+ (:metaclass standard-class))
+@end lisp
+@lisp
+(defclass bad-funcallable-object (standard-object)
+ ()
+ (:metaclass funcallable-standard-class))
+@end lisp
+The following definition is acceptable:
+@lisp
+(defclass mixin ()
+ ((slot :initarg slot)))
+(defclass funcallable-object (funcallable-standard-object mixin)
+ ()
+ (:metaclass funcallable-standard-class))
+@end lisp
+and leads to a class whose instances are funcallable and have one slot.
-@end itemize
+@tindex @sbmop{funcallable-standard-object}
+Note that this requirement also applies to the class
+@code{sb-mop:funcallable-standard-object}, which has metaclass
+@code{sb-mop:funcallable-standard-class} rather than
+@code{standard-class} as AMOP specifies.
+@item
+the requirement that ``No portable class @math{C_p} may inherit, by
+virtue of being a direct or indirect subclass of a specified class, any
+slot for which the name is a symbol accessible in the
+@code{common-lisp-user} package or exported by any package defined in
+the ANSI Common Lisp standard.'' is interpreted to mean that the
+standardized classes themselves should not have slots named by external
+symbols of public packages.
+
+The rationale behind the restriction is likely to be similar to the ANSI
+Common Lisp restriction on defining functions, variables and types named
+by symbols in the Common Lisp package: preventing two independent pieces
+of software from colliding with each other.
-@node Threading
-@comment node-name, next, previous, up
-@subsection Threading (a.k.a Multiprocessing)
+@item
+@findex @sbmop{slot-value-using-class}
+@findex @setf{@sbmop{slot-value-using-class}}
+@findex @sbmop{slot-boundp-using-class}
+specializations of the @code{new-value} argument to @code{(setf
+sb-mop:slot-value-using-class)} are not allowed: all user-defined
+methods must have a specializer of the class @code{t}.
+
+This prohibition is motivated by a separation of layers: the
+@code{slot-value-using-class} family of functions is intended for use in
+implementing different and new slot allocation strategies, rather than
+in performing application-level dispatching. Additionally, with this
+requirement, there is a one-to-one mapping between metaclass, class and
+slot-definition-class tuples and effective methods of @code{(setf
+slot-value-using-class)}, which permits optimization of @code{(setf
+slot-value-using-class)}'s discriminating function in the same manner as
+for @code{slot-value-using-class} and @code{slot-boundp-using-class}.
+
+Note that application code may specialize on the @code{new-value}
+argument of slot accessors.
-SBCL supports a fairly low-level threading interface that maps onto
-the host operating system's concept of threads or lightweight
-processes. This means that threads may take advantage of hardware
-multiprocessing on machines that have more than one CPU, but it does
-not allow Lisp control of the scheduler. This is found in the
-SB-THREAD package.
+@item
+@findex @cl{defclass}
+@findex @sbmop{ensure-class}
+@findex @sbmop{ensure-class-using-class}
+@findex @cl{find-class}
+@findex @cl{class-name}
+the class named by the @code{name} argument to @code{ensure-class}, if
+any, is only redefined if it is the proper name of that class;
+otherwise, a new class is created.
+
+This is consistent with the description of @code{ensure-class} in AMOP
+as the functional version of @code{defclass}, which has this behaviour;
+however, it is not consistent with the weaker requirement in AMOP, which
+states that any class found by @code{find-class}, no matter what its
+@code{class-name}, is redefined.
-This requires x86 and Linux kernel 2.6 or systems with NPTL backports.
+@end itemize
-@subsubsection Special variables
+@subsection Metaobject Protocol Extensions
-The interaction of special variables with multiple threads is mostly
-as one would expect, but users of other Lisps are warned that the
-behaviour of locally bound specials differs in places from what they
-may expect.
+In addition, SBCL supports extensions to the Metaobject protocol from
+AMOP; at present, they are:
@itemize
-@item
-global special values are visible across all threads;
+
@item
-bindings (e.g. using LET) are local to the thread;
+@findex @cl{defmethod}
+@findex @cl{find-class}
+@findex @sbmop{intern-eql-specializer}
+@findex @sbpcl{make-method-specializers-form}
+@findex @sbmop{make-method-lambda}
+compile-time support for generating specializer metaobjects from
+specializer names in @code{defmethod} forms is provided by the
+@code{make-method-specializers-form} function, which returns a form
+which, when evaluated in the lexical environment of the
+@code{defmethod}, returns a list of specializer metaobjects. This
+operator suffers from similar restrictions to those affecting
+@code{make-method-lambda}, namely that the generic function must be
+defined when the @code{defmethod} form is expanded, so that the
+correct method of @code{make-method-specializers-form} is invoked.
+The system-provided method on @code{make-method-specializers-form}
+generates a call to @code{find-class} for each symbol specializer
+name, and a call to @code{intern-eql-specializer} for each @code{(eql
+@var{x})} specializer name.
+
@item
-initial values in a new thread are taken from the thread that created it.
-@end itemize
+@findex @cl{find-method}
+@findex @sbpcl{parse-specializer-using-class}
+@findex @sbpcl{unparse-specializer-using-class}
+run-time support for converting between specializer names and
+specializer metaobjects, mostly for the purposes of
+@code{find-method}, is provided by
+@code{parse-specializer-using-class} and
+@code{unparse-specializer-using-class}, which dispatch on their first
+argument, the generic function associated with a method with the given
+specializer. The system-provided methods on those methods convert
+between classes and proper names and between lists of the form
+@code{(eql @var{x})} and interned eql specializer objects.
+
+@item
+@vindex @sbpcl{+slot-unbound+}
+@findex @sbmop{standard-instance-access}
+@findex @sbmop{funcallable-standard-instance-access}
+distinguishing unbound instance allocated slots from bound ones when
+using @code{standard-instance-access} and
+@code{funcallable-standard-instance-access} is possible by comparison
+to the constant @code{+slot-unbound+}.
-@subsubsection Mutex support
+@end itemize
-Mutexes are used for controlling access to a shared resource. One
-thread is allowed to hold the mutex, others which attempt to take it
-will be made to wait until it's free. Threads are woken in the order
-that they go to sleep.
+@node Extensible Sequences
+@comment node-name, next, previous, up
+@section Extensible Sequences
-There isn't a timeout on mutex acquisition, but the usual WITH-TIMEOUT
-macro (which throws a TIMEOUT condition after n seconds) can be used
-if you want a bounded wait.
+@menu
+* Iterator Protocol::
+* Simple Iterator Protocol::
+@end menu
+ANSI Common Lisp has a class @code{sequence} with subclasses @code{list} and
+@code{vector} on which the ``sequence functions'' like @code{find},
+@code{subseq}, etc. operate. As an extension to the ANSI specification,
+SBCL allows additional subclasses of @code{sequence} to be defined
+@footnote{A motivation, rationale and additional examples for the design
+of this extension can be found in the paper @cite{Rhodes, Christophe
+(2007): User-extensible sequences in Common Lisp} available for download
+at
+@url{http://www.doc.gold.ac.uk/~mas01cr/papers/ilc2007/sequences-20070301.pdf}.}.
+@tindex @cl{sequence}
+@tindex @cl{vector}
+@findex @cl{find}
+@findex @cl{subseq}
+
+Users of this extension just make instances of @cl{sequence} subclasses
+and transparently operate on them using sequence functions:
@lisp
-(defpackage :demo (:use "CL" "SB-THREAD" "SB-EXT"))
+(coerce (subseq (make-instance 'my-sequence) 5 10) 'list)
+@end lisp
+From this perspective, no distinction between builtin and user-defined
+@code{sequence} subclasses should be necessary.
+@findex @cl{coerce}
+@findex @cl{subseq}
+@findex @cl{make-instance}
+@tindex @cl{list}
+
+Providers of the extension, that is of user-defined @code{sequence}
+subclasses, have to adhere to a ``sequence protocol'' which consists of
+a set of generic functions in the @code{sequence} package.
+@c
+A minimal @code{sequence} subclass has to specify @code{standard-object} and
+@code{sequence} as its superclasses and has to be the specializer of the
+@code{sequence} parameter of methods on at least the following generic
+functions:
+@tindex @cl{sequence}
+@tindex @cl{standard-object}
+
+@include fun-sb-sequence-length.texinfo
+@include fun-sb-sequence-elt.texinfo
+@include fun-sb-sequence-setf-elt.texinfo
+@include fun-sb-sequence-adjust-sequence.texinfo
+@include fun-sb-sequence-make-sequence-like.texinfo
+
+@code{make-sequence-like} is needed for functions returning
+freshly-allocated sequences such as @code{subseq} or
+@code{copy-seq}. @code{adjust-sequence} is needed for functions which
+destructively modify their arguments such as @code{delete}. In fact, all
+other sequence functions can be implemented in terms of the above
+functions and actually are, if no additional methods are
+defined. However, relying on these generic implementations, in
+particular not implementing the iterator protocol can incur a high
+performance penalty @xref{Iterator Protocol}.
+@tindex @cl{sequence}
+@findex @sequence{make-sequence-like}
+@findex @cl{subseq}
+@findex @cl{copy-seq}
+@findex @sequence{adjust-sequence}
+
+In addition to the mandatory functions above, methods on the following
+sequence functions can be defined:
+
+@include fun-sb-sequence-emptyp.texinfo
-(in-package :demo)
+@itemize
+@item
+@code{sb-sequence:count}, @code{sb-sequence:count-if}, @code{sb-sequence:count-if-not}
-(defvar *a-mutex* (make-mutex :name "my lock"))
+@item
+@code{sb-sequence:find}, @code{sb-sequence:find-if}, @code{sb-sequence:find-if-not}
-(defun thread-fn ()
- (let ((id (current-thread-id)))
- (format t "Thread ~A running ~%" id)
- (with-mutex (*a-mutex*)
- (format t "Thread ~A got the lock~%" id)
- (sleep (random 5)))
- (format t "Thread ~A dropped lock, dying now~%" id)))
+@item
+@code{sb-sequence:position}, @code{sb-sequence:position-if}, @code{sb-sequence:position-if-not}
-(make-thread #'thread-fn)
-(make-thread #'thread-fn)
+@item
+@code{sb-sequence:subseq}
-@end lisp
+@item
+@code{sb-sequence:copy-seq}
-@subsubsection Waitqueue/condition variables
+@item
+@code{sb-sequence:fill}
-These are based on the POSIX condition variable design, hence the
-annoyingly CL-conflicting name. For use when you want to check a
-condition and sleep until it's true. For example: you have a shared
-queue, a writer process checking ``queue is empty'' and one or more
-readers that need to know when ``queue is not empty''. It sounds
-simple, but is astonishingly easy to deadlock if another process runs
-when you weren't expecting it to.
+@item
+@code{sb-sequence:nsubstitute}, @code{sb-sequence:nsubstitute-if},
+@code{sb-sequence:nsubstitute-if-not}, @code{sb-sequence:substitute},
+@code{sb-sequence:substitute-if}, @code{sb-sequence:substitute-if-not}
-There are three components:
+@item
+@code{sb-sequence:replace}
-@itemize
-@item the condition itself (not represented in code)
-@item the condition variable (a.k.a waitqueue) which proxies for it
-@item a lock to hold while testing the condition
-@end itemize
+@item
+@code{sb-sequence:nreverse}, @code{sb-sequence:reverse}
-Important stuff to be aware of:
+@item
+@code{sb-sequence:reduce}
-@itemize
-@item when calling condition-wait, you must hold the mutex. condition-wait will drop the mutex while it waits, and obtain it again before returning for whatever reason;
+@item
+@code{sb-sequence:mismatch}
+
+@item
+@code{sb-sequence:search}
-@item likewise, you must be holding the mutex around calls to condition-notify;
+@item
+@code{sb-sequence:delete}, @code{sb-sequence:delete-if}, @code{sb-sequence:delete-if-not},
+@code{sb-sequence:remove}, @code{sb-sequence:remove-if}, @code{sb-sequence:remove-if-not},
-@item a process may return from condition-wait in several circumstances: it is not guaranteed that the underlying condition has become true. You must check that the resource is ready for whatever you want to do to it.
+@item
+@code{sb-sequence:delete-duplicates}, @code{sb-sequence:remove-duplicates}
+@item
+@code{sb-sequence:sort}, @code{sb-sequence:stable-sort}
@end itemize
-@lisp
-(defvar *buffer-queue* (make-waitqueue))
-(defvar *buffer-lock* (make-mutex :name "buffer lock"))
-
-(defvar *buffer* (list nil))
-
-(defun reader ()
- (with-mutex (*buffer-lock*)
- (loop
- (condition-wait *buffer-queue* *buffer-lock*)
- (loop
- (unless *buffer* (return))
- (let ((head (car *buffer*)))
- (setf *buffer* (cdr *buffer*))
- (format t "reader ~A woke, read ~A~%"
- (current-thread-id) head))))))
-
-(defun writer ()
- (loop
- (sleep (random 5))
- (with-mutex (*buffer-lock*)
- (let ((el (intern
- (string (code-char
- (+ (char-code #\A) (random 26)))))))
- (setf *buffer* (cons el *buffer*)))
- (condition-notify *buffer-queue*))))
-
-(make-thread #'writer)
-(make-thread #'reader)
-(make-thread #'reader)
+In the spirit of @code{dolist}, generic sequences can be traversed using
+the macro
+@findex @cl{dolist}
-@end lisp
+@include macro-sb-sequence-dosequence.texinfo
+
+@node Iterator Protocol
+@comment node-name, next, previous, up
+@subsection Iterator Protocol
+
+The iterator protocol allows subsequently accessing some or all elements
+of a sequence in forward or reverse direction. Users first call
+@code{make-sequence-iterator} to create an iteration state and
+receive functions to query and mutate it. These functions allow, among
+other things, moving to, retrieving or modifying elements of the
+sequence. An iteration state consists of a state object, a limit object,
+a from-end indicator and the following six functions to query or mutate
+this state:
+@findex @sequence{make-sequence-iterator}
+@deffn {Function} @code{step function} sequence iterator from-end
+Moves the iterator one position forward or backward in the associated
+sequence depending on the iteration direction.
+@end deffn
+@deffn {Function} @code{endp function} sequence iterator limit from-end
+Returns non-@code{nil} when the iterator has reached the end of the
+associated sequence with respect to the iteration direction.
+@end deffn
+@deffn {Function} @code{element function} sequence iterator
+Returns the sequence element associated to the current position of the
+iteration.
+@end deffn
+@deffn {Function} @code{setf element function} new-value sequence iterator
+Destructively modifies the associates sequence by replacing the sequence
+element associated to the current iteration position with a new value.
+@end deffn
+@deffn {Function} @code{index function} sequence iterator
+Returns the position of the iteration in the associated sequence.
+@end deffn
+@deffn {Function} @code{copy function} sequence iterator
+Returns a copy of the iteration state which can be mutated independently
+of the copied iteration state.
+@end deffn
+
+An iterator is created by calling:
+
+@include fun-sb-sequence-make-sequence-iterator.texinfo
+
+Note that @code{make-sequence-iterator} calls
+@code{make-simple-sequence-iterator} when there is no specialized
+method for a particular @code{sequence} subclass. @xref{Simple Iterator
+Protocol}.
+@findex @sequence{make-sequence-iterator}
+@findex @sequence{make-simple-sequence-iterator}
+@tindex @cl{sequence}
+
+The following convenience macros simplify traversing sequences using
+iterators:
+
+@include macro-sb-sequence-with-sequence-iterator.texinfo
+@include macro-sb-sequence-with-sequence-iterator-functions.texinfo
+
+@node Simple Iterator Protocol
+@comment node-name, next, previous, up
+@subsection Simple Iterator Protocol
+
+For cases in which the full flexibility and performance of the general
+sequence iterator protocol is not required, there is a simplified
+sequence iterator protocol consisting of a few generic functions which
+can be specialized for iterator classes:
-@subsubsection Sessions/Debugging
-
-If the user has multiple views onto the same Lisp image (for example,
-using multiple terminals, or a windowing system, or network access)
-they are typically set up as multiple @dfn{sessions} such that each
-view has its own collection of foreground/background/stopped threads.
-A thread which wishes to create a new session can use
-@code{sb-thread:with-new-session} to remove itself from the current
-session (which it shares with its parent and siblings) and create a
-fresh one.
-# See also @code{sb-thread:make-listener-thread}.
-
-Within a single session, threads arbitrate between themselves for the
-user's attention. A thread may be in one of three notional states:
-foreground, background, or stopped. When a background process
-attempts to print a repl prompt or to enter the debugger, it will stop
-and print a message saying that it has stopped. The user at his
-leisure may switch to that thread to find out what it needs. If a
-background thread enters the debugger, selecting any restart will put
-it back into the background before it resumes. Arbitration for the
-input stream is managed by calls to @code{sb-thread:get-foreground}
-(which may block) and @code{sb-thread:release-foreground}.
-
-@code{sb-ext:quit} terminates all threads in the current session, but
-leaves other sessions running.
-
-
-@subsubsection Implementation (Linux x86)
-
-On Linux x86, threading is implemented using @code{clone()} and does
-not involve pthreads. This is not because there is anything wrong
-with pthreads @emph{per se}, but there is plenty wrong (from our
-perspective) with LinuxThreads. SBCL threads are mapped 1:1 onto
-Linux tasks which share a VM but nothing else - each has its own
-process id and can be seen in e.g. @command{ps} output.
-
-Per-thread local bindings for special variables is achieved using the
-%fs segment register to point to a per-thread storage area. This may
-cause interesting results if you link to foreign code that expects
-threading or creates new threads, and the thread library in question
-uses %fs in an incompatible way.
-
-Queues require the @code{sys_futex()} system call to be available:
-this is the reason for the NPTL requirement. We test at runtime that
-this system call exists.
-
-Garbage collection is done with the existing Conservative Generational
-GC. Allocation is done in small (typically 8k) regions: each thread
-has its own region so this involves no stopping. However, when a
-region fills, a lock must be obtained while another is allocated, and
-when a collection is required, all processes are stopped. This is
-achieved by sending them signals, which may make for interesting
-behaviour if they are interrupted in system calls. The streams
-interface is believed to handle the required system call restarting
-correctly, but this may be a consideration when making other blocking
-calls e.g. from foreign library code.
-
-Large amounts of the SBCL library have not been inspected for
-thread-safety. Some of the obviously unsafe areas have large locks
-around them, so compilation and fasl loading, for example, cannot be
-parallelized. Work is ongoing in this area.
-
-A new thread by default is created in the same POSIX process group and
-session as the thread it was created by. This has an impact on
-keyboard interrupt handling: pressing your terminal's intr key
-(typically @kbd{Control-C}) will interrupt all processes in the
-foreground process group, including Lisp threads that SBCL considers
-to be notionally `background'. This is undesirable, so background
-threads are set to ignore the SIGINT signal.
-
-@code{sb-thread:make-listener-thread} in addition to creating a new
-Lisp session makes a new POSIX session, so that pressing
-@kbd{Control-C} in one window will not interrupt another listener -
-this has been found to be embarrassing.
+@include fun-sb-sequence-iterator-step.texinfo
+@include fun-sb-sequence-iterator-endp.texinfo
+@include fun-sb-sequence-iterator-element.texinfo
+@include fun-sb-sequence-setf-iterator-element.texinfo
+@include fun-sb-sequence-iterator-index.texinfo
+@include fun-sb-sequence-iterator-copy.texinfo
+Iterator objects implementing the above simple iteration protocol are
+created by calling the following generic function:
+
+@include fun-sb-sequence-make-simple-sequence-iterator.texinfo
@node Support For Unix
@comment node-name, next, previous, up
-@subsection Support For Unix
+@section Support For Unix
+
+@menu
+* Command-line arguments::
+* Querying the process environment::
+* Running external programs::
+@end menu
+
+@node Command-line arguments
+@subsection Command-line arguments
+@vindex @sbext{@earmuffs{posix-argv}}
The UNIX command line can be read from the variable
-@code{sb-ext:*posix-argv*}. The UNIX environment can be queried with
-the @code{sb-ext:posix-getenv} function.
+@code{sb-ext:*posix-argv*}.
+
+@node Querying the process environment
+@subsection Querying the process environment
+
+The UNIX environment can be queried with the
+@code{sb-ext:posix-getenv} function.
@include fun-sb-ext-posix-getenv.texinfo
-The SBCL system can be terminated with @code{sb-ext:quit}, (but see
-notes in @ref{Threading} about the interaction between this feature and
-sessions) optionally returning a specified numeric value to the
-calling Unix process. The normal Unix idiom of terminating on end of
-file on input is also supported.
+@node Running external programs
+@subsection Running external programs
+
+External programs can be run with @code{sb-ext:run-program}.
+@footnote{In SBCL versions prior to 1.0.13, @code{sb-ext:run-program}
+searched for executables in a manner somewhat incompatible with other
+languages. As of this version, SBCL uses the system library routine
+@code{execvp(3)}, and no longer contains the function,
+@code{find-executable-in-search-path}, which implemented the old
+search. Users who need this function may find it
+in @file{run-program.lisp} versions 1.67 and earlier in SBCL's CVS
+repository here
+@url{http://sbcl.cvs.sourceforge.net/sbcl/sbcl/src/code/run-program.lisp?view=log}. However,
+we caution such users that this search routine finds executables that
+system library routines do not.}
+
+@include fun-sb-ext-run-program.texinfo
+
+When @code{sb-ext:run-program} is called with @code{wait} equal to
+NIL, an instance of class @var{sb-ext:process} is returned. The
+following functions are available for use with processes:
+
+@include fun-sb-ext-process-p.texinfo
+
+@include fun-sb-ext-process-input.texinfo
+
+@include fun-sb-ext-process-output.texinfo
+
+@include fun-sb-ext-process-error.texinfo
+
+@include fun-sb-ext-process-alive-p.texinfo
+
+@include fun-sb-ext-process-status.texinfo
-@include fun-sb-ext-quit.texinfo
+@include fun-sb-ext-process-wait.texinfo
+
+@include fun-sb-ext-process-exit-code.texinfo
+
+@include fun-sb-ext-process-core-dumped.texinfo
+
+@include fun-sb-ext-process-close.texinfo
+
+@include fun-sb-ext-process-kill.texinfo
@node Customization Hooks for Users
@comment node-name, next, previous, up
-@subsection Customization Hooks for Users
+@section Customization Hooks for Users
The toplevel repl prompt may be customized, and the function
that reads user input may be replaced completely.
@include fun-common-lisp-ed.texinfo
@include var-sb-ext-star-ed-functions-star.texinfo
-@node Tools To Help Developers
+Conditions of type @code{warning} and @code{style-warning} are
+sometimes signaled at runtime, especially during execution of Common
+Lisp defining forms such as @code{defun}, @code{defmethod}, etc. To
+muffle these warnings at runtime, SBCL provides a variable
+@code{sb-ext:*muffled-warnings*}:
+
+@include var-sb-ext-star-muffled-warnings-star.texinfo
+
+@node Tools To Help Developers
@comment node-name, next, previous, up
-@subsection Tools To Help Developers
+@section Tools To Help Developers
+@findex @cl{trace}
+@findex @cl{inspect}
SBCL provides a profiler and other extensions to the ANSI @code{trace}
-facility. For more information, see @ref{macro-common-lisp-trace}.
+facility. For more information, see @ref{Macro common-lisp:trace}.
The debugger supports a number of options. Its documentation is
accessed by typing @kbd{help} at the debugger prompt. @xref{Debugger}.
Documentation for @code{inspect} is accessed by typing @kbd{help} at
the @code{inspect} prompt.
-@node Interface To Low-Level SBCL Implementation
+@node Resolution of Name Conflicts
+@section Resolution of Name Conflicts
+@tindex @sbext{name-conflict}
+@findex @sbext{name-conflict-symbols}
+
+The ANSI standard (section 11.1.1.2.5) requires that name conflicts in
+packages be resolvable in favour of any of the conflicting symbols. In
+the interactive debugger, this is achieved by prompting for the symbol
+in whose favour the conflict should be resolved; for programmatic use,
+the @code{sb-ext:resolve-conflict} restart should be invoked with one
+argument, which should be a member of the list returned by the condition
+accessor @code{sb-ext:name-conflict-symbols}.
+
+@node Hash Table Extensions
@comment node-name, next, previous, up
-@subsection Interface To Low-Level SBCL Implementation
+@section Hash Table Extensions
+@cindex Hash tables
-SBCL has the ability to save its state as a file for later
-execution. This functionality is important for its bootstrapping
-process, and is also provided as an extension to the user. Note that
-foreign libraries loaded via @code{load-shared-object} don't survive
-this process; a core should not be saved in this case.
+Hash table extensions supported by SBCL are all controlled by keyword
+arguments to @code{make-hash-table}.
-@emph{FIXME: what should be done for foreign libraries?}
+@include fun-common-lisp-make-hash-table.texinfo
-@emph{FIXME: document load-shared-object somewhere - it's in
-ffi.texinfo?}
+@include macro-sb-ext-define-hash-table-test.texinfo
-@include fun-sb-ext-save-lisp-and-die.texinfo
+@include macro-sb-ext-with-locked-hash-table.texinfo
+@include fun-sb-ext-hash-table-synchronized-p.texinfo
+
+@include fun-sb-ext-hash-table-weakness.texinfo
+
+@node Random Number Generation
+@comment node-name, next, previous, up
+@section Random Number Generation
+@cindex Random Number Generation
+
+The initial value of @code{*random-state*} is the same each time SBCL
+is started. This makes it possible for user code to obtain repeatable
+pseudo random numbers using only standard-provided functionality. See
+@code{seed-random-state} below for an SBCL extension that allows to
+seed the random number generator from given data for an additional
+possibility to achieve this. Non-repeatable random numbers can always
+be obtained using @code{(make-random-state t)}.
+
+The sequence of numbers produced by repeated calls to @code{random}
+starting with the same random state and using the same sequence of
+@code{limit} arguments is guaranteed to be reproducible only in the
+same version of SBCL on the same platform, using the same code under
+the same evaluator mode and compiler optimization qualities. Just two
+examples of differences that may occur otherwise: calls to
+@code{random} can be compiled differently depending on how much is
+known about the @code{limit} argument at compile time, yielding
+different results even if called with the same argument at run time,
+and the results can differ depending on the machine's word size, for
+example for limits that are fixnums under 64-bit word size but bignums
+under 32-bit word size.
+
+@include fun-sb-ext-seed-random-state.texinfo
+
+Some notes on random floats: The standard doesn't prescribe a specific
+method of generating random floats. The following paragraph describes
+SBCL's current implementation and should be taken purely informational,
+that is, user code should not depend on any of its specific properties.
+The method used has been chosen because it is common, conceptually
+simple and fast.
+
+To generate random floats, SBCL evaluates code that has an equivalent
+effect as
+@lisp
+(* limit
+ (float (/ (random (expt 2 23)) (expt 2 23)) 1.0f0))
+@end lisp
+(for single-floats) and correspondingly (with @code{52} and
+@code{1.0d0} instead of @code{23} and @code{1.0f0}) for double-floats.
+Note especially that this means that zero is a possible return value
+occurring with probability @code{(expt 2 -23)} respectively
+@code{(expt 2 -52)}. Also note that there exist twice as many
+equidistant floats between 0 and 1 as are generated. For example, the
+largest number that @code{(random 1.0f0)} ever returns is
+@code{(float (/ (1- (expt 2 23)) (expt 2 23)) 1.0f0)} while
+@code{(float (/ (1- (expt 2 24)) (expt 2 24)) 1.0f0)} is the
+largest single-float less than 1. This is a side effect of the fact
+that the implementation uses the fastest possible conversion from bits
+to floats.
+
+SBCL currently uses the Mersenne Twister as its random number
+generator, specifically the 32-bit version under both 32- and 64-bit
+word size. The seeding algorithm has been improved several times by
+the authors of the Mersenne Twister; SBCL uses the third version
+(from 2002) which is still the most recent as of June 2012. The
+implementation has been tested to provide output identical to the
+recommended C implementation.
+
+While the Mersenne Twister generates random numbers of much better
+statistical quality than other widely used generators, it uses only
+linear operations modulo 2 and thus fails some statistical
+tests@footnote{See chapter 7 "Testing widely used RNGs" in
+@cite{TestU01: A C Library for Empirical Testing of Random Number
+Generators} by Pierre L'Ecuyer and Richard Simard, ACM Transactions on
+Mathematical Software, Vol. 33, article 22, 2007.}.
+For example, the distribution of ranks of (sufficiently large) random
+binary matrices is much distorted compared to the theoretically
+expected one when the matrices are generated by the Mersenne Twister.
+Thus, applications that are sensitive to this aspect should use a
+different type of generator.
+
+@node Miscellaneous Extensions
+@comment node-name, next, previous, up
+@section Miscellaneous Extensions
+
+@include fun-sb-ext-array-storage-vector.texinfo
+@include fun-sb-ext-delete-directory.texinfo
+@include fun-sb-ext-get-time-of-day.texinfo
+@include macro-sb-ext-wait-for.texinfo
+@include fun-sb-ext-version-assert.texinfo
@node Stale Extensions
@comment node-name, next, previous, up
-@subsection Stale Extensions
+@section Stale Extensions
SBCL has inherited from CMUCL various hooks to allow the user to
tweak and monitor the garbage collection process. These are somewhat
@node Efficiency Hacks
@comment node-name, next, previous, up
-@subsection Efficiency Hacks
+@section Efficiency Hacks
The @code{sb-ext:purify} function causes SBCL first to collect all
-garbage, then to mark all uncollected objects as permanent, never
-again attempting to collect them as garbage. This can cause a large
-increase in efficiency when using a primitive garbage collector, or a
-more moderate increase in efficiency when using a more sophisticated
-garbage collector which is well suited to the program's memory usage
-pattern. It also allows permanent code to be frozen at fixed
-addresses, a precondition for using copy-on-write to share code
-between multiple Lisp processes. it is less important with modern
-generational garbage collectors.
+garbage, then to mark all uncollected objects as permanent, never again
+attempting to collect them as garbage. This can cause a large increase
+in efficiency when using a primitive garbage collector, or a more
+moderate increase in efficiency when using a more sophisticated garbage
+collector which is well suited to the program's memory usage pattern. It
+also allows permanent code to be frozen at fixed addresses, a
+precondition for using copy-on-write to share code between multiple Lisp
+processes. This is less important with modern generational garbage
+collectors, but not all SBCL platforms use such a garbage collector.
@include fun-sb-ext-purify.texinfo
The @code{sb-ext:freeze-type} declaration declares that a
type will never change, which can make type testing
(@code{typep}, etc.) more efficient for structure types.
-
-The @code{sb-ext:constant-function} declaration specifies
-that a function will always return the same value for the same
-arguments, which may allow the compiler to optimize calls
-to it. This is appropriate for functions like @code{sqrt}, but
-is @emph{not} appropriate for functions like @code{aref},
-which can change their return values when the underlying data are
-changed.
-@c <!-- FIXME: This declaration does not seem to be supported in the
-@c current compiler. -->
projects / sbcl.git / blobdiff