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 ****************************************************************************/
144 # define GC_cdecl GC_CALLBACK
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 ) && ! defined( __WATCOMC__ ) \
164 && (!defined(_MSC_VER) || _MSC_VER > 1020)
165 # define GC_PLACEMENT_DELETE
168 enum GCPlacement {UseGC,
169 #ifndef GC_NAME_CONFLICT
172 NoGC, PointerFreeGC};
175 inline void* operator new( size_t size );
176 inline void* operator new( size_t size, GCPlacement gcp );
177 inline void* operator new( size_t size, void *p );
178 /* Must be redefined here, since the other overloadings */
179 /* hide the global definition. */
180 inline void operator delete( void* obj );
181 # ifdef GC_PLACEMENT_DELETE
182 inline void operator delete( void*, GCPlacement );
183 /* called if construction fails. */
184 inline void operator delete( void*, void* );
187 #ifdef GC_OPERATOR_NEW_ARRAY
188 inline void* operator new[]( size_t size );
189 inline void* operator new[]( size_t size, GCPlacement gcp );
190 inline void* operator new[]( size_t size, void *p );
191 inline void operator delete[]( void* obj );
192 # ifdef GC_PLACEMENT_DELETE
193 inline void operator delete[]( void*, GCPlacement );
194 inline void operator delete[]( void*, void* );
196 #endif /* GC_OPERATOR_NEW_ARRAY */
199 Instances of classes derived from "gc" will be allocated in the
200 collected heap by default, unless an explicit NoGC placement is
203 class gc_cleanup: virtual public gc {public:
205 inline virtual ~gc_cleanup();
207 inline static void GC_cdecl cleanup( void* obj, void* clientData );};
209 Instances of classes derived from "gc_cleanup" will be allocated
210 in the collected heap by default. When the collector discovers an
211 inaccessible object derived from "gc_cleanup" or containing a
212 member derived from "gc_cleanup", its destructors will be
216 typedef void (GC_CALLBACK * GCCleanUpFunc)( void* obj, void* clientData );
220 // Disable warning that "no matching operator delete found; memory will
221 // not be freed if initialization throws an exception"
222 # pragma warning(disable:4291)
225 inline void* operator new(
228 GCCleanUpFunc cleanup = 0,
229 void* clientData = 0 );
231 Allocates a collectable or uncollected object, according to the
234 For collectable objects, if "cleanup" is non-null, then when the
235 allocated object "obj" becomes inaccessible, the collector will
236 invoke the function "cleanup( obj, clientData )" but will not
237 invoke the object's destructors. It is an error to explicitly
238 delete an object allocated with a non-null "cleanup".
240 It is an error to specify a non-null "cleanup" with NoGC or for
241 classes derived from "gc_cleanup" or containing members derived
242 from "gc_cleanup". */
244 # ifdef GC_PLACEMENT_DELETE
245 inline void operator delete( void*, GCPlacement, GCCleanUpFunc, void * );
249 /** This ensures that the system default operator new[] doesn't get
250 * undefined, which is what seems to happen on VC++ 6 for some reason
251 * if we define a multi-argument operator new[].
252 * There seems to be no way to redirect new in this environment without
253 * including this everywhere.
256 void *operator new[]( size_t size );
258 void operator delete[](void* obj);
261 void* operator new( size_t size);
263 void operator delete(void* obj);
265 // This new operator is used by VC++ in case of Debug builds !
266 void* operator new( size_t size,
268 const char * szFileName,
270 #endif /* _MSC_VER */
273 #ifdef GC_OPERATOR_NEW_ARRAY
275 inline void* operator new[](
278 GCCleanUpFunc cleanup = 0,
279 void* clientData = 0 );
281 The operator new for arrays, identical to the above. */
283 #endif /* GC_OPERATOR_NEW_ARRAY */
285 /****************************************************************************
287 Inline implementation
289 ****************************************************************************/
291 inline void* gc::operator new( size_t size ) {
292 return GC_MALLOC( size );}
294 inline void* gc::operator new( size_t size, GCPlacement gcp ) {
296 return GC_MALLOC( size );
297 else if (gcp == PointerFreeGC)
298 return GC_MALLOC_ATOMIC( size );
300 return GC_MALLOC_UNCOLLECTABLE( size );}
302 inline void* gc::operator new( size_t size, void *p ) {
305 inline void gc::operator delete( void* obj ) {
308 #ifdef GC_PLACEMENT_DELETE
309 inline void gc::operator delete( void*, void* ) {}
311 inline void gc::operator delete( void* p, GCPlacement gcp ) {
316 #ifdef GC_OPERATOR_NEW_ARRAY
318 inline void* gc::operator new[]( size_t size ) {
319 return gc::operator new( size );}
321 inline void* gc::operator new[]( size_t size, GCPlacement gcp ) {
322 return gc::operator new( size, gcp );}
324 inline void* gc::operator new[]( size_t size, void *p ) {
327 inline void gc::operator delete[]( void* obj ) {
328 gc::operator delete( obj );}
330 #ifdef GC_PLACEMENT_DELETE
331 inline void gc::operator delete[]( void*, void* ) {}
333 inline void gc::operator delete[]( void* p, GCPlacement gcp ) {
334 gc::operator delete(p); }
338 #endif /* GC_OPERATOR_NEW_ARRAY */
341 inline gc_cleanup::~gc_cleanup() {
342 GC_register_finalizer_ignore_self( GC_base(this), 0, 0, 0, 0 );}
344 inline void GC_CALLBACK gc_cleanup::cleanup( void* obj, void* displ ) {
345 ((gc_cleanup*) ((char*) obj + (ptrdiff_t) displ))->~gc_cleanup();}
347 inline gc_cleanup::gc_cleanup() {
348 GC_finalization_proc oldProc;
350 void* base = GC_base( (void *) this );
352 // Don't call the debug version, since this is a real base address.
353 GC_register_finalizer_ignore_self(
354 base, (GC_finalization_proc)cleanup, (void*) ((char*) this - (char*) base),
355 &oldProc, &oldData );
357 GC_register_finalizer_ignore_self( base, oldProc, oldData, 0, 0 );}}}
359 inline void* operator new(
362 GCCleanUpFunc cleanup,
368 obj = GC_MALLOC( size );
370 GC_REGISTER_FINALIZER_IGNORE_SELF(
371 obj, cleanup, clientData, 0, 0 );}
372 else if (gcp == PointerFreeGC) {
373 obj = GC_MALLOC_ATOMIC( size );}
375 obj = GC_MALLOC_UNCOLLECTABLE( size );};
378 # ifdef GC_PLACEMENT_DELETE
379 inline void operator delete (
382 GCCleanUpFunc cleanup,
389 #ifdef GC_OPERATOR_NEW_ARRAY
391 inline void* operator new[](
394 GCCleanUpFunc cleanup,
397 return ::operator new( size, gcp, cleanup, clientData );}
399 #endif /* GC_OPERATOR_NEW_ARRAY */
402 #endif /* GC_CPP_H */