2 This file is part of LilyPond, the GNU music typesetter.
4 Copyright (C) 1999--2015 Han-Wen Nienhuys <hanwen@xs4all.nl>
6 LilyPond is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 LilyPond is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with LilyPond. If not, see <http://www.gnu.org/licenses/>.
23 #include "lily-guile.hh"
24 #include "lily-proto.hh"
29 Smobs are GUILEs mechanism of exporting C(++) objects to the Scheme
30 world. They are documented in the GUILE manual.
33 In LilyPond, C++ objects can be placed under the control of GUILE's
34 type system and garbage collection mechanism by inheriting from one
35 of several Smob base classes.
37 There are two types of smob objects.
39 1. Simple smobs are intended for simple objects like numbers:
40 immutable objects that can be copied without change of meaning.
42 To obtain an SCM version of a simple smob, use the member function
45 Simple smobs are created by deriving from Simple_smob<Classname>.
47 A simple smob is only optionally under the reign of the GUILE
48 garbage collector: its usual life time is that of a normal C++
49 object. While a smobbed_copy () is fully under control of the
50 garbage collector and will have its mark_smob function called during
51 garbage collection, an automatic variable of this type will not have
52 mark_smob called, but rather have its memory image in the call stack
53 scanned for contained non-immediate SCM values. Anything requiring
54 more complex mark_smob behavior is not suitable for a simple smob.
56 When you create a smobbed_copy, the _copy_ is fully managed by the
57 GUILE memory system. As a corollary, multiple smobbed_copy calls
58 yield multiple GUILE objects generally not eq? to each other.
60 2. Complex smobs are objects that have an identity. These objects
61 carry this identity in the form of a self_scm () method, which is a
62 SCM pointer to the object itself. Complex smobs are always under
63 control of the GUILE memory system.
65 The constructor for a complex smob should have 3 steps:
67 * initialize all SCM members to an immediate value (like SCM_EOL)
69 * call smobify_self ()
71 * initialize SCM members
75 Complex_smob::Complex_smob : public Smob<Complex_smob> () {
76 scm_member_ = SCM_EOL;
78 scm_member_ = <..what you want to store..>
81 after construction, the self_scm () field of a complex smob is
82 protected from Garbage Collection. This protection should be
83 removed once the object is put into another (reachable) Scheme data
86 Complex_smob *p = new Complex_smob;
87 list = scm_cons (p->self_scm (), list);
90 Since unprotect returns the SCM object itself, this particular case
93 Complex_smob *p = new Complex_smob;
94 list = scm_cons (p->unprotect (), list);
96 Complex smobs are created by deriving from Smob<Classname>.
100 Common global functions for accessing C++ smob objects:
102 - unsmob<T> (SCM x) - unpack X and return a pointer to the C++ object,
103 or 0 if it has the wrong type.
107 For implementating a class, the following public members can be
108 provided in the top class itself:
110 - SCM equal_p (SCM a, SCM b) - compare A and B. Returns a Scheme
111 boolean. If the class does not define this function, equal? will
112 be equivalent to eq?. The function will only be called when both
113 objects are of the respective type and not eq? to each other.
115 - mark_smob () function, that calls scm_gc_mark () on all Scheme
116 objects in the class. If the class does not define this function,
117 it must not contain non-immediate Scheme values.
119 - a print_smob () function, that displays a representation for
120 debugging purposes. If the class does not define this function,
121 the output will be #<Classname> when printing.
123 - a static const * const type_p_name_ string set to something like
124 "ly:grob?". When provided, an accordingly named function for
125 checking for the given smob type will be available in Scheme.
129 // Initialization class. Create a variable or static data member of
130 // this type at global scope (or creation will happen too late for
131 // Scheme initialization), initialising with a function to be called.
132 // Reference somewhere (like in the constructor of the containing
133 // class) to make sure the variable is actually instantiated.
136 static const Scm_init * list_;
137 void (*const fun_)(void);
138 Scm_init const * const next_;
139 Scm_init (); // don't use default constructor, don't define
140 Scm_init (const Scm_init &); // don't define copy constructor
142 Scm_init (void (*fun) (void)) : fun_ (fun), next_ (list_)
147 template <class Super>
150 static scm_t_bits smob_tag_;
151 static Scm_init scm_init_;
152 static void init (void);
153 static string smob_name_;
155 static Super *unchecked_unsmob (SCM s)
157 return reinterpret_cast<Super *> (SCM_SMOB_DATA (s));
159 // reference scm_init_ in smob_tag which is sure to be called. The
160 // constructor, in contrast, may not be called at all in classes
162 static scm_t_bits smob_tag () { (void) scm_init_; return smob_tag_; }
164 static SCM register_ptr (Super *p);
165 static Super *unregister_ptr (SCM obj);
167 // Those fallbacks are _only_ for internal use by Smob_base. They
168 // are characterized by no knowledge about the implemented type
169 // apart from the type's name. Overriding them as a template
170 // specialization is _not_ intended since a type-dependent
171 // implementation will in general need access to possibly private
172 // parts of the Super class. So any class-dependent override should
173 // be done by redefining the respective function in the Super class
174 // (where it will mask the private template member) rather than
175 // specializing a different template function/pointer.
177 // Most default functions are do-nothings. void init() will
178 // recognize their address when not overriden and will then refrain
179 // altogether from passing the the respective callbacks to GUILE.
181 SCM mark_smob (void) const;
182 static SCM mark_trampoline (SCM); // Used for calling mark_smob
183 static size_t free_smob (SCM obj);
184 static SCM equal_p (SCM, SCM);
185 int print_smob (SCM, scm_print_state *) const;
186 static int print_trampoline (SCM, SCM, scm_print_state *);
187 static void smob_proc_init (scm_t_bits) { };
189 // Define type_p_name_ in the Super class as a const char * const.
190 // Without such definition it defaults to 0, producing no predicate.
192 static const char * const type_p_name_; // = 0
194 // LY_DECLARE_SMOB_PROC is used in the Super class definition for
195 // making a smob callable like a function. Its first argument is a
196 // function member pointer constant, to a function taking the
197 // correct number of SCM arguments and returning SCM. The function
198 // itself has to be defined separately.
200 #define LY_DECLARE_SMOB_PROC(PMF, REQ, OPT, VAR) \
201 static void smob_proc_init (scm_t_bits smob_tag) \
203 scm_set_smob_apply (smob_tag, \
204 (scm_t_subr)smob_trampoline<PMF>, \
208 // Well, function template argument packs are a C++11 feature. So
209 // we just define a bunch of trampolines manually. It turns out
210 // that GUILEĀ 1.8.8 cannot actually make callable structures with
211 // more than 3 arguments anyway. That's surprising, to say the
212 // least, but in emergency situations one can always use a "rest"
213 // argument and take it apart manually.
215 template <SCM (Super::*pmf)(void)>
216 static SCM smob_trampoline (SCM self)
218 return (Super::unchecked_unsmob (self)->*pmf)();
220 template <SCM (Super::*pmf)(SCM)>
221 static SCM smob_trampoline (SCM self, SCM arg1)
223 return (Super::unchecked_unsmob (self)->*pmf)(arg1);
225 template <SCM (Super::*pmf)(SCM, SCM)>
226 static SCM smob_trampoline (SCM self, SCM arg1, SCM arg2)
228 return (Super::unchecked_unsmob (self)->*pmf)(arg1, arg2);
230 template <SCM (Super::*pmf)(SCM, SCM, SCM)>
231 static SCM smob_trampoline (SCM self, SCM arg1, SCM arg2, SCM arg3)
233 return (Super::unchecked_unsmob (self)->*pmf)(arg1, arg2, arg3);
236 static bool is_smob (SCM s)
238 return SCM_SMOB_PREDICATE (smob_tag (), s);
240 static SCM smob_p (SCM s)
242 return is_smob (s) ? SCM_BOOL_T : SCM_BOOL_F;
246 friend T *unsmob (SCM s);
249 friend T *ly_assert_smob (SCM s, int number, const char *fun);
253 inline T *unsmob (SCM s)
255 return T::is_smob (s) ? dynamic_cast<T *> (T::unchecked_unsmob (s)) : 0;
259 template <class Super>
260 class Simple_smob : public Smob_base<Super> {
262 static size_t free_smob (SCM obj)
264 delete Smob_base<Super>::unregister_ptr (obj);
267 SCM smobbed_copy () const
269 Super *p = new Super(*static_cast<const Super *> (this));
270 return Smob_base<Super>::register_ptr (p);
274 void protect_smob (SCM smob, SCM *prot_cons);
275 void unprotect_smob (SCM smob, SCM *prot_cons);
277 // The Smob_core class is not templated and contains material not
278 // depending on the Super class.
283 Smob_core () : self_scm_ (SCM_UNDEFINED) { };
285 SCM self_scm () const { return self_scm_; }
286 Listener get_listener (SCM callback);
289 template <class Super>
290 class Smob : public Smob_core, public Smob_base<Super> {
292 SCM protection_cons_;
293 Smob (const Smob<Super> &); // Do not define! Not copyable!
295 Smob () : protection_cons_ (SCM_EOL) { };
297 static size_t free_smob (SCM obj)
299 delete Smob_base<Super>::unregister_ptr (obj);
302 SCM unprotected_smobify_self ()
304 SCM s = Smob_base<Super>::register_ptr (static_cast<Super *> (this));
310 protect_smob (self_scm_, &protection_cons_);
312 void smobify_self () {
313 protect_smob (unprotected_smobify_self (), &protection_cons_);
318 unprotect_smob (s, &protection_cons_);
323 extern bool parsed_objects_should_be_dead;
326 static vector<parsed_dead *> elements;
331 data = SCM_UNDEFINED;
335 parsed_dead () : data (SCM_UNDEFINED)
337 elements.push_back (this);
339 void checkin (SCM arg) { data = arg; }
340 static SCM readout ();
343 // This does not appear to work with GUILEv2's garbage collector:
344 // Objects are found in the GC phase but printing them will crash at
345 // least some, so they are apparently not protected in spite of being
346 // included in the GC scans. So it would appear that scanning smobs
347 // is not equivalent to marking them. Ugh.
348 #if defined(DEBUG) && !GUILEV2
349 #define ASSERT_LIVE_IS_ALLOWED(arg) \
351 static parsed_dead pass_here; \
352 if (parsed_objects_should_be_dead) \
353 pass_here.checkin (arg); \
356 #define ASSERT_LIVE_IS_ALLOWED(arg) do { (void)(arg); } \
361 #endif /* SMOBS_HH */