doc/ref/api-smobs.texi

   1 @c -*-texinfo-*-
   2 @c This is part of the GNU Guile Reference Manual.
   3 @c Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2009, 2013
   4 @c   Free Software Foundation, Inc.
   5 @c See the file guile.texi for copying conditions.
   6
   7 @node Smobs
   8 @section Smobs
   9
  10 @cindex smob
  11
  12 This chapter contains reference information related to defining and
  13 working with smobs.  See @ref{Defining New Types (Smobs)} for a
  14 tutorial-like introduction to smobs.
  15
  16 @deftypefun scm_t_bits scm_make_smob_type (const char *name, size_t size)
  17 This function adds a new smob type, named @var{name}, with instance size
  18 @var{size}, to the system.  The return value is a tag that is used in
  19 creating instances of the type.
  20
  21 If @var{size} is 0, the default @emph{free} function will do nothing.
  22
  23 If @var{size} is not 0, the default @emph{free} function will
  24 deallocate the memory block pointed to by @code{SCM_SMOB_DATA} with
  25 @code{scm_gc_free}.  The @var{what} parameter in the call to
  26 @code{scm_gc_free} will be @var{name}.
  27
  28 Default values are provided for the @emph{mark}, @emph{free},
  29 @emph{print}, and @emph{equalp} functions, as described in
  30 @ref{Defining New Types (Smobs)}.  If you want to customize any of
  31 these functions, the call to @code{scm_make_smob_type} should be
  32 immediately followed by calls to one or several of
  33 @code{scm_set_smob_mark}, @code{scm_set_smob_free},
  34 @code{scm_set_smob_print}, and/or @code{scm_set_smob_equalp}.
  35 @end deftypefun
  36
  37 @cindex finalizer
  38 @cindex finalization
  39
  40 @deftypefn {C Function} void scm_set_smob_free (scm_t_bits tc, size_t (*free) (SCM obj))
  41 This function sets the smob freeing procedure (sometimes referred to as
  42 a @dfn{finalizer}) for the smob type specified by the tag
  43 @var{tc}. @var{tc} is the tag returned by @code{scm_make_smob_type}.
  44
  45 The @var{free} procedure must deallocate all resources that are
  46 directly associated with the smob instance @var{obj}.  It must assume
  47 that all @code{SCM} values that it references have already been freed
  48 and are thus invalid.
  49
  50 It must also not call any libguile function or macro except
  51 @code{scm_gc_free}, @code{SCM_SMOB_FLAGS}, @code{SCM_SMOB_DATA},
  52 @code{SCM_SMOB_DATA_2}, and @code{SCM_SMOB_DATA_3}.
  53
  54 The @var{free} procedure must return 0.
  55
  56 Note that defining a freeing procedure is not necessary if the resources
  57 associated with @var{obj} consists only of memory allocated with
  58 @code{scm_gc_malloc} or @code{scm_gc_malloc_pointerless} because this
  59 memory is automatically reclaimed by the garbage collector when it is no
  60 longer needed (@pxref{Memory Blocks, @code{scm_gc_malloc}}).
  61 @end deftypefn
  62
  63 @cindex precise marking
  64
  65 @deftypefn {C Function} void scm_set_smob_mark (scm_t_bits tc, SCM (*mark) (SCM obj))
  66 This function sets the smob marking procedure for the smob type specified by
  67 the tag @var{tc}. @var{tc} is the tag returned by @code{scm_make_smob_type}.
  68
  69 Defining a marking procedure may sometimes be unnecessary because large
  70 parts of the process' memory (with the exception of
  71 @code{scm_gc_malloc_pointerless} regions, and @code{malloc}- or
  72 @code{scm_malloc}-allocated memory) are scanned for live
  73 pointers@footnote{Conversely, in Guile up to the 1.8 series, the marking
  74 procedure was always required.  The reason is that Guile's GC would only
  75 look for pointers in the memory area used for built-in types (the
  76 @dfn{cell heap}), not in user-allocated or statically allocated memory.
  77 This approach is often referred to as @dfn{precise marking}.}.
  78
  79 The @var{mark} procedure must cause @code{scm_gc_mark} to be called
  80 for every @code{SCM} value that is directly referenced by the smob
  81 instance @var{obj}.  One of these @code{SCM} values can be returned
  82 from the procedure and Guile will call @code{scm_gc_mark} for it.
  83 This can be used to avoid deep recursions for smob instances that form
  84 a list.
  85
  86 It must not call any libguile function or macro except
  87 @code{scm_gc_mark}, @code{SCM_SMOB_FLAGS}, @code{SCM_SMOB_DATA},
  88 @code{SCM_SMOB_DATA_2}, and @code{SCM_SMOB_DATA_3}.
  89 @end deftypefn
  90
  91
  92 @deftypefn {C Function} void scm_set_smob_print (scm_t_bits tc, int (*print) (SCM obj, SCM port, scm_print_state* pstate))
  93 This function sets the smob printing procedure for the smob type
  94 specified by the tag @var{tc}. @var{tc} is the tag returned by
  95 @code{scm_make_smob_type}.
  96
  97 The @var{print} procedure should output a textual representation of
  98 the smob instance @var{obj} to @var{port}, using information in
  99 @var{pstate}.
 100
 101 The textual representation should be of the form @code{#<name ...>}.
 102 This ensures that @code{read} will not interpret it as some other
 103 Scheme value.
 104
 105 It is often best to ignore @var{pstate} and just print to @var{port}
 106 with @code{scm_display}, @code{scm_write}, @code{scm_simple_format},
 107 and @code{scm_puts}.
 108 @end deftypefn
 109
 110 @deftypefn {C Function} void scm_set_smob_equalp (scm_t_bits tc, SCM (*equalp) (SCM obj1, SCM obj2))
 111 This function sets the smob equality-testing predicate for the smob
 112 type specified by the tag @var{tc}. @var{tc} is the tag returned by
 113 @code{scm_make_smob_type}.
 114
 115 The @var{equalp} procedure should return @code{SCM_BOOL_T} when
 116 @var{obj1} is @code{equal?} to @var{obj2}.  Else it should return
 117 @code{SCM_BOOL_F}.  Both @var{obj1} and @var{obj2} are instances of the
 118 smob type @var{tc}.
 119 @end deftypefn
 120
 121 @deftypefn {C Function} void scm_assert_smob_type (scm_t_bits tag, SCM val)
 122 When @var{val} is a smob of the type indicated by @var{tag}, do nothing.
 123 Else, signal an error.
 124 @end deftypefn
 125
 126 @deftypefn {C Macro} int SCM_SMOB_PREDICATE (scm_t_bits tag, SCM exp)
 127 Return true iff @var{exp} is a smob instance of the type indicated by
 128 @var{tag}.  The expression @var{exp} can be evaluated more than once,
 129 so it shouldn't contain any side effects.
 130 @end deftypefn
 131
 132 @deftypefn {C Function} SCM scm_new_smob (scm_t_bits tag, void *data)
 133 @deftypefnx {C Function} SCM scm_new_double_smob (scm_t_bits tag, void *data, void *data2, void *data3)
 134 Make a new smob of the type with tag @var{tag} and smob data @var{data},
 135 @var{data2}, and @var{data3}, as appropriate.
 136
 137 The @var{tag} is what has been returned by @code{scm_make_smob_type}.
 138 The initial values @var{data}, @var{data2}, and @var{data3} are of
 139 type @code{scm_t_bits}; when you want to use them for @code{SCM}
 140 values, these values need to be converted to a @code{scm_t_bits} first
 141 by using @code{SCM_UNPACK}.
 142
 143 The flags of the smob instance start out as zero.
 144 @end deftypefn
 145
 146 @deftypefn {C Macro} scm_t_bits SCM_SMOB_FLAGS (SCM obj)
 147 Return the 16 extra bits of the smob @var{obj}.  No meaning is
 148 predefined for these bits, you can use them freely.
 149 @end deftypefn
 150
 151 @deftypefn {C Macro} scm_t_bits SCM_SET_SMOB_FLAGS (SCM obj, scm_t_bits flags)
 152 Set the 16 extra bits of the smob @var{obj} to @var{flags}.  No
 153 meaning is predefined for these bits, you can use them freely.
 154 @end deftypefn
 155
 156 @deftypefn {C Macro} scm_t_bits SCM_SMOB_DATA (SCM obj)
 157 @deftypefnx {C Macro} scm_t_bits SCM_SMOB_DATA_2 (SCM obj)
 158 @deftypefnx {C Macro} scm_t_bits SCM_SMOB_DATA_3 (SCM obj)
 159 Return the first (second, third) immediate word of the smob @var{obj}
 160 as a @code{scm_t_bits} value.  When the word contains a @code{SCM}
 161 value, use @code{SCM_SMOB_OBJECT} (etc.) instead.
 162 @end deftypefn
 163
 164 @deftypefn {C Macro} void SCM_SET_SMOB_DATA (SCM obj, scm_t_bits val)
 165 @deftypefnx {C Macro} void SCM_SET_SMOB_DATA_2 (SCM obj, scm_t_bits val)
 166 @deftypefnx {C Macro} void SCM_SET_SMOB_DATA_3 (SCM obj, scm_t_bits val)
 167 Set the first (second, third) immediate word of the smob @var{obj} to
 168 @var{val}.  When the word should be set to a @code{SCM} value, use
 169 @code{SCM_SMOB_SET_OBJECT} (etc.) instead.
 170 @end deftypefn
 171
 172 @deftypefn {C Macro} SCM SCM_SMOB_OBJECT (SCM obj)
 173 @deftypefnx {C Macro} SCM SCM_SMOB_OBJECT_2 (SCM obj)
 174 @deftypefnx {C Macro} SCM SCM_SMOB_OBJECT_3 (SCM obj)
 175 Return the first (second, third) immediate word of the smob @var{obj}
 176 as a @code{SCM} value.  When the word contains a @code{scm_t_bits}
 177 value, use @code{SCM_SMOB_DATA} (etc.) instead.
 178 @end deftypefn
 179
 180 @deftypefn {C Macro} void SCM_SET_SMOB_OBJECT (SCM obj, SCM val)
 181 @deftypefnx {C Macro} void SCM_SET_SMOB_OBJECT_2 (SCM obj, SCM val)
 182 @deftypefnx {C Macro} void SCM_SET_SMOB_OBJECT_3 (SCM obj, SCM val)
 183 Set the first (second, third) immediate word of the smob @var{obj} to
 184 @var{val}.  When the word should be set to a @code{scm_t_bits} value, use
 185 @code{SCM_SMOB_SET_DATA} (etc.) instead.
 186 @end deftypefn
 187
 188 @deftypefn {C Macro} {SCM *} SCM_SMOB_OBJECT_LOC (SCM obj)
 189 @deftypefnx {C Macro} {SCM *} SCM_SMOB_OBJECT_2_LOC (SCM obj)
 190 @deftypefnx {C Macro} {SCM *} SCM_SMOB_OBJECT_3_LOC (SCM obj)
 191 Return a pointer to the first (second, third) immediate word of the
 192 smob @var{obj}.  Note that this is a pointer to @code{SCM}.  If you
 193 need to work with @code{scm_t_bits} values, use @code{SCM_PACK} and
 194 @code{SCM_UNPACK}, as appropriate.
 195 @end deftypefn
 196
 197 @deftypefun SCM scm_markcdr (SCM @var{x})
 198 Mark the references in the smob @var{x}, assuming that @var{x}'s first
 199 data word contains an ordinary Scheme object, and @var{x} refers to no
 200 other objects.  This function simply returns @var{x}'s first data word.
 201 @end deftypefun
 202
 203 @c Local Variables:
 204 @c TeX-master: "guile.texi"
 205 @c End: