boehm-gc/gc_cpp.h

   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     Last modified on Mon Jul 24 15:43:42 PDT 1995 by ellis
  20
  21 This interface provides access to the Boehm collector.  It provides
  22 basic facilities similar to those described in "Safe, Efficient
  23 Garbage Collection for C++", by John R. Elis and David L. Detlefs
  24 (ftp.parc.xerox.com:/pub/ellis/gc).
  25
  26 All heap-allocated objects are either "collectable" or
  27 "uncollectable".  Programs must explicitly delete uncollectable
  28 objects, whereas the garbage collector will automatically delete
  29 collectable objects when it discovers them to be inaccessible.
  30 Collectable objects may freely point at uncollectable objects and vice
  31 versa.
  32
  33 Objects allocated with the built-in "::operator new" are uncollectable.
  34
  35 Objects derived from class "gc" are collectable.  For example:
  36
  37     class A: public gc {...};
  38     A* a = new A;       // a is collectable.
  39
  40 Collectable instances of non-class types can be allocated using the GC
  41 placement:
  42
  43     typedef int A[ 10 ];
  44     A* a = new (GC) A;
  45
  46 Uncollectable instances of classes derived from "gc" can be allocated
  47 using the NoGC placement:
  48
  49     class A: public gc {...};
  50     A* a = new (NoGC) A;   // a is uncollectable.
  51
  52 Both uncollectable and collectable objects can be explicitly deleted
  53 with "delete", which invokes an object's destructors and frees its
  54 storage immediately.
  55
  56 A collectable object may have a clean-up function, which will be
  57 invoked when the collector discovers the object to be inaccessible.
  58 An object derived from "gc_cleanup" or containing a member derived
  59 from "gc_cleanup" has a default clean-up function that invokes the
  60 object's destructors.  Explicit clean-up functions may be specified as
  61 an additional placement argument:
  62
  63     A* a = ::new (GC, MyCleanup) A;
  64
  65 An object is considered "accessible" by the collector if it can be
  66 reached by a path of pointers from static variables, automatic
  67 variables of active functions, or from some object with clean-up
  68 enabled; pointers from an object to itself are ignored.
  69
  70 Thus, if objects A and B both have clean-up functions, and A points at
  71 B, B is considered accessible.  After A's clean-up is invoked and its
  72 storage released, B will then become inaccessible and will have its
  73 clean-up invoked.  If A points at B and B points to A, forming a
  74 cycle, then that's considered a storage leak, and neither will be
  75 collectable.  See the interface gc.h for low-level facilities for
  76 handling such cycles of objects with clean-up.
  77
  78 The collector cannot guarrantee that it will find all inaccessible
  79 objects.  In practice, it finds almost all of them.
  80
  81
  82 Cautions:
  83
  84 1. Be sure the collector has been augmented with "make c++".
  85
  86 2.  If your compiler supports the new "operator new[]" syntax, then
  87 add -DOPERATOR_NEW_ARRAY to the Makefile.
  88
  89 If your compiler doesn't support "operator new[]", beware that an
  90 array of type T, where T is derived from "gc", may or may not be
  91 allocated as a collectable object (it depends on the compiler).  Use
  92 the explicit GC placement to make the array collectable.  For example:
  93
  94     class A: public gc {...};
  95     A* a1 = new A[ 10 ];        // collectable or uncollectable?
  96     A* a2 = new (GC) A[ 10 ];   // collectable
  97
  98 3. The destructors of collectable arrays of objects derived from
  99 "gc_cleanup" will not be invoked properly.  For example:
 100
 101     class A: public gc_cleanup {...};
 102     A* a = new (GC) A[ 10 ];    // destructors not invoked correctly
 103
 104 Typically, only the destructor for the first element of the array will
 105 be invoked when the array is garbage-collected.  To get all the
 106 destructors of any array executed, you must supply an explicit
 107 clean-up function:
 108
 109     A* a = new (GC, MyCleanUp) A[ 10 ];
 110
 111 (Implementing clean-up of arrays correctly, portably, and in a way
 112 that preserves the correct exception semantics requires a language
 113 extension, e.g. the "gc" keyword.)
 114
 115 4. Compiler bugs:
 116
 117 * Solaris 2's CC (SC3.0) doesn't implement t->~T() correctly, so the
 118 destructors of classes derived from gc_cleanup won't be invoked.
 119 You'll have to explicitly register a clean-up function with
 120 new-placement syntax.
 121
 122 * Evidently cfront 3.0 does not allow destructors to be explicitly
 123 invoked using the ANSI-conforming syntax t->~T().  If you're using
 124 cfront 3.0, you'll have to comment out the class gc_cleanup, which
 125 uses explicit invocation.
 126
 127 ****************************************************************************/
 128
 129 #include "gc.h"
 130
 131 #ifndef THINK_CPLUS
 132 #define _cdecl
 133 #endif
 134
 135 #if ! defined( OPERATOR_NEW_ARRAY ) \
 136     && (__BORLANDC__ >= 0x450 || (__GNUC__ >= 2 && __GNUC_MINOR__ >= 6))
 137 #   define OPERATOR_NEW_ARRAY
 138 #endif
 139
 140 enum GCPlacement {GC, NoGC, PointerFreeGC};
 141
 142 class gc {public:
 143     inline void* operator new( size_t size );
 144     inline void* operator new( size_t size, GCPlacement gcp );
 145     inline void operator delete( void* obj );
 146
 147 #ifdef OPERATOR_NEW_ARRAY
 148     inline void* operator new[]( size_t size );
 149     inline void* operator new[]( size_t size, GCPlacement gcp );
 150     inline void operator delete[]( void* obj );
 151 #endif /* OPERATOR_NEW_ARRAY */
 152     };
 153     /*
 154     Instances of classes derived from "gc" will be allocated in the
 155     collected heap by default, unless an explicit NoGC placement is
 156     specified. */
 157
 158 class gc_cleanup: virtual public gc {public:
 159     inline gc_cleanup();
 160     inline virtual ~gc_cleanup();
 161 private:
 162     inline static void _cdecl cleanup( void* obj, void* clientData );};
 163     /*
 164     Instances of classes derived from "gc_cleanup" will be allocated
 165     in the collected heap by default.  When the collector discovers an
 166     inaccessible object derived from "gc_cleanup" or containing a
 167     member derived from "gc_cleanup", its destructors will be
 168     invoked. */
 169
 170 extern "C" {typedef void (*GCCleanUpFunc)( void* obj, void* clientData );}
 171
 172 inline void* operator new(
 173     size_t size,
 174     GCPlacement gcp,
 175     GCCleanUpFunc cleanup = 0,
 176     void* clientData = 0 );
 177     /*
 178     Allocates a collectable or uncollected object, according to the
 179     value of "gcp".
 180
 181     For collectable objects, if "cleanup" is non-null, then when the
 182     allocated object "obj" becomes inaccessible, the collector will
 183     invoke the function "cleanup( obj, clientData )" but will not
 184     invoke the object's destructors.  It is an error to explicitly
 185     delete an object allocated with a non-null "cleanup".
 186
 187     It is an error to specify a non-null "cleanup" with NoGC or for
 188     classes derived from "gc_cleanup" or containing members derived
 189     from "gc_cleanup". */
 190
 191 #ifdef OPERATOR_NEW_ARRAY
 192
 193 inline void* operator new[](
 194     size_t size,
 195     GCPlacement gcp,
 196     GCCleanUpFunc cleanup = 0,
 197     void* clientData = 0 );
 198     /*
 199     The operator new for arrays, identical to the above. */
 200
 201 #endif /* OPERATOR_NEW_ARRAY */
 202
 203 /****************************************************************************
 204
 205 Inline implementation
 206
 207 ****************************************************************************/
 208
 209 inline void* gc::operator new( size_t size ) {
 210     return GC_MALLOC( size );}
 211
 212 inline void* gc::operator new( size_t size, GCPlacement gcp ) {
 213     if (gcp == GC)
 214         return GC_MALLOC( size );
 215     else
 216         return GC_MALLOC_UNCOLLECTABLE( size );}
 217
 218 inline void gc::operator delete( void* obj ) {
 219     GC_FREE( obj );}
 220
 221
 222 #ifdef OPERATOR_NEW_ARRAY
 223
 224 inline void* gc::operator new[]( size_t size ) {
 225     return gc::operator new( size );}
 226
 227 inline void* gc::operator new[]( size_t size, GCPlacement gcp ) {
 228     return gc::operator new( size, gcp );}
 229
 230 inline void gc::operator delete[]( void* obj ) {
 231     gc::operator delete( obj );}
 232
 233 #endif /* OPERATOR_NEW_ARRAY */
 234
 235
 236 inline gc_cleanup::~gc_cleanup() {
 237     GC_REGISTER_FINALIZER_IGNORE_SELF( this, 0, 0, 0, 0 );}
 238
 239 inline void gc_cleanup::cleanup( void* obj, void* displ ) {
 240     ((gc_cleanup*) ((char*) obj + (ptrdiff_t) displ))->~gc_cleanup();}
 241
 242 inline gc_cleanup::gc_cleanup() {
 243     GC_finalization_proc oldProc;
 244     void* oldData;
 245     void* base = GC_base( (void *) this );
 246     if (0 == base) return;
 247     GC_REGISTER_FINALIZER_IGNORE_SELF(
 248         base, cleanup, (void*) ((char*) this - (char*) base),
 249         &oldProc, &oldData );
 250     if (0 != oldProc) {
 251         GC_REGISTER_FINALIZER_IGNORE_SELF( base, oldProc, oldData, 0, 0 );}}
 252
 253 inline void* operator new(
 254     size_t size,
 255     GCPlacement gcp,
 256     GCCleanUpFunc cleanup,
 257     void* clientData )
 258 {
 259     void* obj;
 260
 261     if (gcp == GC) {
 262         obj = GC_MALLOC( size );
 263         if (cleanup != 0)
 264             GC_REGISTER_FINALIZER_IGNORE_SELF(
 265                 obj, cleanup, clientData, 0, 0 );}
 266     else if (gcp == PointerFreeGC) {
 267         obj = GC_MALLOC_ATOMIC( size );}
 268     else {
 269         obj = GC_MALLOC_UNCOLLECTABLE( size );};
 270     return obj;}
 271
 272
 273 #ifdef OPERATOR_NEW_ARRAY
 274
 275 inline void* operator new[](
 276     size_t size,
 277     GCPlacement gcp,
 278     GCCleanUpFunc cleanup,
 279     void* clientData )
 280 {
 281     return ::operator new( size, gcp, cleanup, clientData );}
 282
 283 #endif /* OPERATOR_NEW_ARRAY */
 284
 285
 286 #endif /* GC_CPP_H */
 287