Annotation of OpenXM_contrib/gc/gc_cpp.h, Revision 1.1.1.2
1.1 maekawa 1: #ifndef GC_CPP_H
2: #define GC_CPP_H
3: /****************************************************************************
4: Copyright (c) 1994 by Xerox Corporation. All rights reserved.
5:
6: THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
7: OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
8:
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: ****************************************************************************
15:
16: C++ Interface to the Boehm Collector
17:
18: John R. Ellis and Jesse Hull
19:
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
1.1.1.2 ! maekawa 23: (ftp://ftp.parc.xerox.com/pub/ellis/gc).
1.1 maekawa 24:
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
30: versa.
31:
32: Objects allocated with the built-in "::operator new" are uncollectable.
33:
34: Objects derived from class "gc" are collectable. For example:
35:
36: class A: public gc {...};
37: A* a = new A; // a is collectable.
38:
39: Collectable instances of non-class types can be allocated using the GC
1.1.1.2 ! maekawa 40: (or UseGC) placement:
1.1 maekawa 41:
42: typedef int A[ 10 ];
43: A* a = new (GC) A;
44:
45: Uncollectable instances of classes derived from "gc" can be allocated
46: using the NoGC placement:
47:
48: class A: public gc {...};
49: A* a = new (NoGC) A; // a is uncollectable.
50:
51: Both uncollectable and collectable objects can be explicitly deleted
52: with "delete", which invokes an object's destructors and frees its
53: storage immediately.
54:
55: A collectable object may have a clean-up function, which will be
56: invoked when the collector discovers the object to be inaccessible.
57: An object derived from "gc_cleanup" or containing a member derived
58: from "gc_cleanup" has a default clean-up function that invokes the
59: object's destructors. Explicit clean-up functions may be specified as
60: an additional placement argument:
61:
62: A* a = ::new (GC, MyCleanup) A;
63:
64: An object is considered "accessible" by the collector if it can be
65: reached by a path of pointers from static variables, automatic
66: variables of active functions, or from some object with clean-up
67: enabled; pointers from an object to itself are ignored.
68:
69: Thus, if objects A and B both have clean-up functions, and A points at
70: B, B is considered accessible. After A's clean-up is invoked and its
71: storage released, B will then become inaccessible and will have its
72: clean-up invoked. If A points at B and B points to A, forming a
73: cycle, then that's considered a storage leak, and neither will be
74: collectable. See the interface gc.h for low-level facilities for
75: handling such cycles of objects with clean-up.
76:
77: The collector cannot guarrantee that it will find all inaccessible
78: objects. In practice, it finds almost all of them.
79:
80:
81: Cautions:
82:
83: 1. Be sure the collector has been augmented with "make c++".
84:
85: 2. If your compiler supports the new "operator new[]" syntax, then
86: add -DOPERATOR_NEW_ARRAY to the Makefile.
87:
88: If your compiler doesn't support "operator new[]", beware that an
89: array of type T, where T is derived from "gc", may or may not be
90: allocated as a collectable object (it depends on the compiler). Use
91: the explicit GC placement to make the array collectable. For example:
92:
93: class A: public gc {...};
94: A* a1 = new A[ 10 ]; // collectable or uncollectable?
95: A* a2 = new (GC) A[ 10 ]; // collectable
96:
97: 3. The destructors of collectable arrays of objects derived from
98: "gc_cleanup" will not be invoked properly. For example:
99:
100: class A: public gc_cleanup {...};
101: A* a = new (GC) A[ 10 ]; // destructors not invoked correctly
102:
103: Typically, only the destructor for the first element of the array will
104: be invoked when the array is garbage-collected. To get all the
105: destructors of any array executed, you must supply an explicit
106: clean-up function:
107:
108: A* a = new (GC, MyCleanUp) A[ 10 ];
109:
110: (Implementing clean-up of arrays correctly, portably, and in a way
111: that preserves the correct exception semantics requires a language
112: extension, e.g. the "gc" keyword.)
113:
114: 4. Compiler bugs:
115:
116: * Solaris 2's CC (SC3.0) doesn't implement t->~T() correctly, so the
117: destructors of classes derived from gc_cleanup won't be invoked.
118: You'll have to explicitly register a clean-up function with
119: new-placement syntax.
120:
121: * Evidently cfront 3.0 does not allow destructors to be explicitly
122: invoked using the ANSI-conforming syntax t->~T(). If you're using
123: cfront 3.0, you'll have to comment out the class gc_cleanup, which
124: uses explicit invocation.
125:
1.1.1.2 ! maekawa 126: 5. GC name conflicts:
! 127:
! 128: Many other systems seem to use the identifier "GC" as an abbreviation
! 129: for "Graphics Context". Since version 5.0, GC placement has been replaced
! 130: by UseGC. GC is an alias for UseGC, unless GC_NAME_CONFLICT is defined.
! 131:
1.1 maekawa 132: ****************************************************************************/
133:
134: #include "gc.h"
135:
136: #ifndef THINK_CPLUS
137: #define _cdecl
138: #endif
139:
140: #if ! defined( OPERATOR_NEW_ARRAY ) \
141: && (__BORLANDC__ >= 0x450 || (__GNUC__ >= 2 && __GNUC_MINOR__ >= 6) \
1.1.1.2 ! maekawa 142: || __WATCOMC__ >= 1050 || _MSC_VER >= 1100)
1.1 maekawa 143: # define OPERATOR_NEW_ARRAY
144: #endif
145:
1.1.1.2 ! maekawa 146: enum GCPlacement {UseGC,
! 147: #ifndef GC_NAME_CONFLICT
! 148: GC=UseGC,
! 149: #endif
! 150: NoGC, PointerFreeGC};
1.1 maekawa 151:
152: class gc {public:
153: inline void* operator new( size_t size );
154: inline void* operator new( size_t size, GCPlacement gcp );
155: inline void operator delete( void* obj );
156:
157: #ifdef OPERATOR_NEW_ARRAY
158: inline void* operator new[]( size_t size );
159: inline void* operator new[]( size_t size, GCPlacement gcp );
160: inline void operator delete[]( void* obj );
161: #endif /* OPERATOR_NEW_ARRAY */
162: };
163: /*
164: Instances of classes derived from "gc" will be allocated in the
165: collected heap by default, unless an explicit NoGC placement is
166: specified. */
167:
168: class gc_cleanup: virtual public gc {public:
169: inline gc_cleanup();
170: inline virtual ~gc_cleanup();
171: private:
172: inline static void _cdecl cleanup( void* obj, void* clientData );};
173: /*
174: Instances of classes derived from "gc_cleanup" will be allocated
175: in the collected heap by default. When the collector discovers an
176: inaccessible object derived from "gc_cleanup" or containing a
177: member derived from "gc_cleanup", its destructors will be
178: invoked. */
179:
180: extern "C" {typedef void (*GCCleanUpFunc)( void* obj, void* clientData );}
181:
182: inline void* operator new(
183: size_t size,
184: GCPlacement gcp,
185: GCCleanUpFunc cleanup = 0,
186: void* clientData = 0 );
187: /*
188: Allocates a collectable or uncollected object, according to the
189: value of "gcp".
190:
191: For collectable objects, if "cleanup" is non-null, then when the
192: allocated object "obj" becomes inaccessible, the collector will
193: invoke the function "cleanup( obj, clientData )" but will not
194: invoke the object's destructors. It is an error to explicitly
195: delete an object allocated with a non-null "cleanup".
196:
197: It is an error to specify a non-null "cleanup" with NoGC or for
198: classes derived from "gc_cleanup" or containing members derived
199: from "gc_cleanup". */
200:
201: #ifdef OPERATOR_NEW_ARRAY
202:
1.1.1.2 ! maekawa 203: #ifdef _MSC_VER
! 204: /** This ensures that the system default operator new[] doesn't get
! 205: * undefined, which is what seems to happen on VC++ 6 for some reason
! 206: * if we define a multi-argument operator new[].
! 207: */
! 208: inline void *operator new[]( size_t size )
! 209: {
! 210: return ::operator new( size );
! 211: }
! 212: #endif /* _MSC_VER */
! 213:
1.1 maekawa 214: inline void* operator new[](
215: size_t size,
216: GCPlacement gcp,
217: GCCleanUpFunc cleanup = 0,
218: void* clientData = 0 );
219: /*
220: The operator new for arrays, identical to the above. */
221:
222: #endif /* OPERATOR_NEW_ARRAY */
223:
224: /****************************************************************************
225:
226: Inline implementation
227:
228: ****************************************************************************/
229:
230: inline void* gc::operator new( size_t size ) {
231: return GC_MALLOC( size );}
232:
233: inline void* gc::operator new( size_t size, GCPlacement gcp ) {
1.1.1.2 ! maekawa 234: if (gcp == UseGC)
1.1 maekawa 235: return GC_MALLOC( size );
236: else if (gcp == PointerFreeGC)
237: return GC_MALLOC_ATOMIC( size );
238: else
239: return GC_MALLOC_UNCOLLECTABLE( size );}
240:
241: inline void gc::operator delete( void* obj ) {
242: GC_FREE( obj );}
243:
244:
245: #ifdef OPERATOR_NEW_ARRAY
246:
247: inline void* gc::operator new[]( size_t size ) {
248: return gc::operator new( size );}
249:
250: inline void* gc::operator new[]( size_t size, GCPlacement gcp ) {
251: return gc::operator new( size, gcp );}
252:
253: inline void gc::operator delete[]( void* obj ) {
254: gc::operator delete( obj );}
255:
256: #endif /* OPERATOR_NEW_ARRAY */
257:
258:
259: inline gc_cleanup::~gc_cleanup() {
260: GC_REGISTER_FINALIZER_IGNORE_SELF( GC_base(this), 0, 0, 0, 0 );}
261:
262: inline void gc_cleanup::cleanup( void* obj, void* displ ) {
263: ((gc_cleanup*) ((char*) obj + (ptrdiff_t) displ))->~gc_cleanup();}
264:
265: inline gc_cleanup::gc_cleanup() {
266: GC_finalization_proc oldProc;
267: void* oldData;
268: void* base = GC_base( (void *) this );
1.1.1.2 ! maekawa 269: if (0 != base) {
! 270: GC_REGISTER_FINALIZER_IGNORE_SELF(
! 271: base, (GC_finalization_proc)cleanup, (void*) ((char*) this - (char*) base),
1.1 maekawa 272: &oldProc, &oldData );
1.1.1.2 ! maekawa 273: if (0 != oldProc) {
! 274: GC_REGISTER_FINALIZER_IGNORE_SELF( base, oldProc, oldData, 0, 0 );}}}
1.1 maekawa 275:
276: inline void* operator new(
277: size_t size,
278: GCPlacement gcp,
279: GCCleanUpFunc cleanup,
280: void* clientData )
281: {
282: void* obj;
283:
1.1.1.2 ! maekawa 284: if (gcp == UseGC) {
1.1 maekawa 285: obj = GC_MALLOC( size );
286: if (cleanup != 0)
287: GC_REGISTER_FINALIZER_IGNORE_SELF(
288: obj, cleanup, clientData, 0, 0 );}
289: else if (gcp == PointerFreeGC) {
290: obj = GC_MALLOC_ATOMIC( size );}
291: else {
292: obj = GC_MALLOC_UNCOLLECTABLE( size );};
293: return obj;}
294:
295:
296: #ifdef OPERATOR_NEW_ARRAY
297:
298: inline void* operator new[](
299: size_t size,
300: GCPlacement gcp,
301: GCCleanUpFunc cleanup,
302: void* clientData )
303: {
304: return ::operator new( size, gcp, cleanup, clientData );}
305:
306: #endif /* OPERATOR_NEW_ARRAY */
307:
308:
309: #endif /* GC_CPP_H */
310:
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