3 /****************************************************************************
4 Copyright (c) 1994 by Xerox Corporation. All rights reserved.
6 THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
7 OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
9 Permission is hereby granted to use or copy this program for any
10 purpose, provided the above notices are retained on all copies.
11 Permission to modify the code and to distribute modified code is
12 granted, provided the above notices are retained, and a notice that
13 the code was modified is included with the above copyright notice.
14 ****************************************************************************
16 C++ Interface to the Boehm Collector
18 John R. Ellis and Jesse Hull
20 This interface provides access to the Boehm collector. It provides
21 basic facilities similar to those described in "Safe, Efficient
22 Garbage Collection for C++", by John R. Elis and David L. Detlefs
23 (ftp://ftp.parc.xerox.com/pub/ellis/gc).
25 All heap-allocated objects are either "collectable" or
26 "uncollectable". Programs must explicitly delete uncollectable
27 objects, whereas the garbage collector will automatically delete
28 collectable objects when it discovers them to be inaccessible.
29 Collectable objects may freely point at uncollectable objects and vice
32 Objects allocated with the built-in "::operator new" are uncollectable.
34 Objects derived from class "gc" are collectable. For example:
36 class A: public gc {...};
37 A* a = new A; // a is collectable.
39 Collectable instances of non-class types can be allocated using the GC
45 Uncollectable instances of classes derived from "gc" can be allocated
46 using the NoGC placement:
48 class A: public gc {...};
49 A* a = new (NoGC) A; // a is uncollectable.
51 The new(PointerFreeGC) syntax allows the allocation of collectable
52 objects that are not scanned by the collector. This useful if you
53 are allocating compressed data, bitmaps, or network packets. (In
54 the latter case, it may remove danger of unfriendly network packets
55 intentionally containing values that cause spurious memory retention.)
57 Both uncollectable and collectable objects can be explicitly deleted
58 with "delete", which invokes an object's destructors and frees its
61 A collectable object may have a clean-up function, which will be
62 invoked when the collector discovers the object to be inaccessible.
63 An object derived from "gc_cleanup" or containing a member derived
64 from "gc_cleanup" has a default clean-up function that invokes the
65 object's destructors. Explicit clean-up functions may be specified as
66 an additional placement argument:
68 A* a = ::new (GC, MyCleanup) A;
70 An object is considered "accessible" by the collector if it can be
71 reached by a path of pointers from static variables, automatic
72 variables of active functions, or from some object with clean-up
73 enabled; pointers from an object to itself are ignored.
75 Thus, if objects A and B both have clean-up functions, and A points at
76 B, B is considered accessible. After A's clean-up is invoked and its
77 storage released, B will then become inaccessible and will have its
78 clean-up invoked. If A points at B and B points to A, forming a
79 cycle, then that's considered a storage leak, and neither will be
80 collectable. See the interface gc.h for low-level facilities for
81 handling such cycles of objects with clean-up.
83 The collector cannot guarantee that it will find all inaccessible
84 objects. In practice, it finds almost all of them.
89 1. Be sure the collector has been augmented with "make c++" or
92 2. If your compiler supports the new "operator new[]" syntax, then
93 add -DGC_OPERATOR_NEW_ARRAY to the Makefile.
95 If your compiler doesn't support "operator new[]", beware that an
96 array of type T, where T is derived from "gc", may or may not be
97 allocated as a collectable object (it depends on the compiler). Use
98 the explicit GC placement to make the array collectable. For example:
100 class A: public gc {...};
101 A* a1 = new A[ 10 ]; // collectable or uncollectable?
102 A* a2 = new (GC) A[ 10 ]; // collectable
104 3. The destructors of collectable arrays of objects derived from
105 "gc_cleanup" will not be invoked properly. For example:
107 class A: public gc_cleanup {...};
108 A* a = new (GC) A[ 10 ]; // destructors not invoked correctly
110 Typically, only the destructor for the first element of the array will
111 be invoked when the array is garbage-collected. To get all the
112 destructors of any array executed, you must supply an explicit
115 A* a = new (GC, MyCleanUp) A[ 10 ];
117 (Implementing clean-up of arrays correctly, portably, and in a way
118 that preserves the correct exception semantics requires a language
119 extension, e.g. the "gc" keyword.)
121 4. Compiler bugs (now hopefully history):
123 * Solaris 2's CC (SC3.0) doesn't implement t->~T() correctly, so the
124 destructors of classes derived from gc_cleanup won't be invoked.
125 You'll have to explicitly register a clean-up function with
126 new-placement syntax.
128 * Evidently cfront 3.0 does not allow destructors to be explicitly
129 invoked using the ANSI-conforming syntax t->~T(). If you're using
130 cfront 3.0, you'll have to comment out the class gc_cleanup, which
131 uses explicit invocation.
133 5. GC name conflicts:
135 Many other systems seem to use the identifier "GC" as an abbreviation
136 for "Graphics Context". Since version 5.0, GC placement has been replaced
137 by UseGC. GC is an alias for UseGC, unless GC_NAME_CONFLICT is defined.
139 ****************************************************************************/
146 # define GC_cdecl _cdecl
149 #if ! defined( GC_NO_OPERATOR_NEW_ARRAY ) \
150 && !defined(_ENABLE_ARRAYNEW) /* Digimars */ \
151 && (defined(__BORLANDC__) && (__BORLANDC__ < 0x450) \
152 || (defined(__GNUC__) && \
153 (__GNUC__ < 2 || __GNUC__ == 2 && __GNUC_MINOR__ < 6)) \
154 || (defined(__WATCOMC__) && __WATCOMC__ < 1050))
155 # define GC_NO_OPERATOR_NEW_ARRAY
158 #if !defined(GC_NO_OPERATOR_NEW_ARRAY) && !defined(GC_OPERATOR_NEW_ARRAY)
159 # define GC_OPERATOR_NEW_ARRAY
162 #if ! defined ( __BORLANDC__ ) /* Confuses the Borland compiler. */ \
163 && ! defined ( __sgi )
164 # define GC_PLACEMENT_DELETE
167 enum GCPlacement
{UseGC
,
168 #ifndef GC_NAME_CONFLICT
171 NoGC
, PointerFreeGC
};
174 inline void* operator new( size_t size
);
175 inline void* operator new( size_t size
, GCPlacement gcp
);
176 inline void* operator new( size_t size
, void *p
);
177 /* Must be redefined here, since the other overloadings */
178 /* hide the global definition. */
179 inline void operator delete( void* obj
);
180 # ifdef GC_PLACEMENT_DELETE
181 inline void operator delete( void*, void* );
184 #ifdef GC_OPERATOR_NEW_ARRAY
185 inline void* operator new[]( size_t size
);
186 inline void* operator new[]( size_t size
, GCPlacement gcp
);
187 inline void* operator new[]( size_t size
, void *p
);
188 inline void operator delete[]( void* obj
);
189 # ifdef GC_PLACEMENT_DELETE
190 inline void operator delete[]( void*, void* );
192 #endif /* GC_OPERATOR_NEW_ARRAY */
195 Instances of classes derived from "gc" will be allocated in the
196 collected heap by default, unless an explicit NoGC placement is
199 class gc_cleanup
: virtual public gc
{public:
201 inline virtual ~gc_cleanup();
203 inline static void GC_cdecl
cleanup( void* obj
, void* clientData
);};
205 Instances of classes derived from "gc_cleanup" will be allocated
206 in the collected heap by default. When the collector discovers an
207 inaccessible object derived from "gc_cleanup" or containing a
208 member derived from "gc_cleanup", its destructors will be
211 extern "C" {typedef void (*GCCleanUpFunc
)( void* obj
, void* clientData
);}
214 // Disable warning that "no matching operator delete found; memory will
215 // not be freed if initialization throws an exception"
216 # pragma warning(disable:4291)
219 inline void* operator new(
222 GCCleanUpFunc cleanup
= 0,
223 void* clientData
= 0 );
225 Allocates a collectable or uncollected object, according to the
228 For collectable objects, if "cleanup" is non-null, then when the
229 allocated object "obj" becomes inaccessible, the collector will
230 invoke the function "cleanup( obj, clientData )" but will not
231 invoke the object's destructors. It is an error to explicitly
232 delete an object allocated with a non-null "cleanup".
234 It is an error to specify a non-null "cleanup" with NoGC or for
235 classes derived from "gc_cleanup" or containing members derived
236 from "gc_cleanup". */
240 /** This ensures that the system default operator new[] doesn't get
241 * undefined, which is what seems to happen on VC++ 6 for some reason
242 * if we define a multi-argument operator new[].
243 * There seems to be really redirect new in this environment without
244 * including this everywhere.
246 void *operator new[]( size_t size
);
248 void operator delete[](void* obj
);
250 void* operator new( size_t size
);
252 void operator delete(void* obj
);
254 // This new operator is used by VC++ in case of Debug builds !
255 void* operator new( size_t size
,
257 const char * szFileName
,
259 #endif /* _MSC_VER */
262 #ifdef GC_OPERATOR_NEW_ARRAY
264 inline void* operator new[](
267 GCCleanUpFunc cleanup
= 0,
268 void* clientData
= 0 );
270 The operator new for arrays, identical to the above. */
272 #endif /* GC_OPERATOR_NEW_ARRAY */
274 /****************************************************************************
276 Inline implementation
278 ****************************************************************************/
280 inline void* gc::operator new( size_t size
) {
281 return GC_MALLOC( size
);}
283 inline void* gc::operator new( size_t size
, GCPlacement gcp
) {
285 return GC_MALLOC( size
);
286 else if (gcp
== PointerFreeGC
)
287 return GC_MALLOC_ATOMIC( size
);
289 return GC_MALLOC_UNCOLLECTABLE( size
);}
291 inline void* gc::operator new( size_t size
, void *p
) {
294 inline void gc::operator delete( void* obj
) {
297 #ifdef GC_PLACEMENT_DELETE
298 inline void gc::operator delete( void*, void* ) {}
301 #ifdef GC_OPERATOR_NEW_ARRAY
303 inline void* gc::operator new[]( size_t size
) {
304 return gc::operator new( size
);}
306 inline void* gc::operator new[]( size_t size
, GCPlacement gcp
) {
307 return gc::operator new( size
, gcp
);}
309 inline void* gc::operator new[]( size_t size
, void *p
) {
312 inline void gc::operator delete[]( void* obj
) {
313 gc::operator delete( obj
);}
315 #ifdef GC_PLACEMENT_DELETE
316 inline void gc::operator delete[]( void*, void* ) {}
319 #endif /* GC_OPERATOR_NEW_ARRAY */
322 inline gc_cleanup::~gc_cleanup() {
323 GC_register_finalizer_ignore_self( GC_base(this), 0, 0, 0, 0 );}
325 inline void gc_cleanup::cleanup( void* obj
, void* displ
) {
326 ((gc_cleanup
*) ((char*) obj
+ (ptrdiff_t) displ
))->~gc_cleanup();}
328 inline gc_cleanup::gc_cleanup() {
329 GC_finalization_proc oldProc
;
331 void* base
= GC_base( (void *) this );
333 // Don't call the debug version, since this is a real base address.
334 GC_register_finalizer_ignore_self(
335 base
, (GC_finalization_proc
)cleanup
, (void*) ((char*) this - (char*) base
),
336 &oldProc
, &oldData
);
338 GC_register_finalizer_ignore_self( base
, oldProc
, oldData
, 0, 0 );}}}
340 inline void* operator new(
343 GCCleanUpFunc cleanup
,
349 obj
= GC_MALLOC( size
);
351 GC_REGISTER_FINALIZER_IGNORE_SELF(
352 obj
, cleanup
, clientData
, 0, 0 );}
353 else if (gcp
== PointerFreeGC
) {
354 obj
= GC_MALLOC_ATOMIC( size
);}
356 obj
= GC_MALLOC_UNCOLLECTABLE( size
);};
360 #ifdef GC_OPERATOR_NEW_ARRAY
362 inline void* operator new[](
365 GCCleanUpFunc cleanup
,
368 return ::operator new( size
, gcp
, cleanup
, clientData
);}
370 #endif /* GC_OPERATOR_NEW_ARRAY */
373 #endif /* GC_CPP_H */