boehm-gc/include/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
  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).
  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
  40 (or UseGC) placement:
  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 -DGC_OPERATOR_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
 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
 132 ****************************************************************************/
 133
 134 #include "gc.h"
 135
 136 #ifndef THINK_CPLUS
 137 #  define GC_cdecl
 138 #else
 139 #  define GC_cdecl _cdecl
 140 #endif
 141
 142 #if ! defined( GC_NO_OPERATOR_NEW_ARRAY ) \
 143     && !defined(_ENABLE_ARRAYNEW) /* Digimars */ \
 144     && (defined(__BORLANDC__) && (__BORLANDC__ < 0x450) \
 145         || (defined(__GNUC__) && \
 146             (__GNUC__ < 2 || __GNUC__ == 2 && __GNUC_MINOR__ < 6)) \
 147         || (defined(__WATCOMC__) && __WATCOMC__ < 1050))
 148 #   define GC_NO_OPERATOR_NEW_ARRAY
 149 #endif
 150
 151 #if !defined(GC_NO_OPERATOR_NEW_ARRAY) && !defined(GC_OPERATOR_NEW_ARRAY)
 152 #   define GC_OPERATOR_NEW_ARRAY
 153 #endif
 154
 155 enum GCPlacement {UseGC,
 156 #ifndef GC_NAME_CONFLICT
 157                   GC=UseGC,
 158 #endif
 159                   NoGC, PointerFreeGC};
 160
 161 class gc {public:
 162     inline void* operator new( size_t size );
 163     inline void* operator new( size_t size, GCPlacement gcp );
 164     inline void* operator new( size_t size, void *p );
 165         /* Must be redefined here, since the other overloadings */
 166         /* hide the global definition.                          */
 167     inline void operator delete( void* obj );
 168 #   ifndef __BORLANDC__  /* Confuses the Borland compiler. */
 169       inline void operator delete( void*, void* );
 170 #   endif
 171
 172 #ifdef GC_OPERATOR_NEW_ARRAY
 173     inline void* operator new[]( size_t size );
 174     inline void* operator new[]( size_t size, GCPlacement gcp );
 175     inline void* operator new[]( size_t size, void *p );
 176     inline void operator delete[]( void* obj );
 177 #   ifndef __BORLANDC__
 178       inline void gc::operator delete[]( void*, void* );
 179 #   endif
 180 #endif /* GC_OPERATOR_NEW_ARRAY */
 181     };
 182     /*
 183     Instances of classes derived from "gc" will be allocated in the
 184     collected heap by default, unless an explicit NoGC placement is
 185     specified. */
 186
 187 class gc_cleanup: virtual public gc {public:
 188     inline gc_cleanup();
 189     inline virtual ~gc_cleanup();
 190 private:
 191     inline static void GC_cdecl cleanup( void* obj, void* clientData );};
 192     /*
 193     Instances of classes derived from "gc_cleanup" will be allocated
 194     in the collected heap by default.  When the collector discovers an
 195     inaccessible object derived from "gc_cleanup" or containing a
 196     member derived from "gc_cleanup", its destructors will be
 197     invoked. */
 198
 199 extern "C" {typedef void (*GCCleanUpFunc)( void* obj, void* clientData );}
 200
 201 #ifdef _MSC_VER
 202   // Disable warning that "no matching operator delete found; memory will
 203   // not be freed if initialization throws an exception"
 204 # pragma warning(disable:4291)
 205 #endif
 206
 207 inline void* operator new(
 208     size_t size,
 209     GCPlacement gcp,
 210     GCCleanUpFunc cleanup = 0,
 211     void* clientData = 0 );
 212     /*
 213     Allocates a collectable or uncollected object, according to the
 214     value of "gcp".
 215
 216     For collectable objects, if "cleanup" is non-null, then when the
 217     allocated object "obj" becomes inaccessible, the collector will
 218     invoke the function "cleanup( obj, clientData )" but will not
 219     invoke the object's destructors.  It is an error to explicitly
 220     delete an object allocated with a non-null "cleanup".
 221
 222     It is an error to specify a non-null "cleanup" with NoGC or for
 223     classes derived from "gc_cleanup" or containing members derived
 224     from "gc_cleanup". */
 225
 226
 227 #ifdef _MSC_VER
 228  /** This ensures that the system default operator new[] doesn't get
 229   *  undefined, which is what seems to happen on VC++ 6 for some reason
 230   *  if we define a multi-argument operator new[].
 231   *  There seems to be really redirect new in this environment without
 232   *  including this everywhere.
 233   */
 234  void *operator new[]( size_t size );
 235
 236  void operator delete[](void* obj);
 237
 238  void* operator new( size_t size);
 239
 240  void operator delete(void* obj);
 241
 242  // This new operator is used by VC++ in case of Debug builds !
 243  void* operator new(  size_t size,
 244                       int ,//nBlockUse,
 245                       const char * szFileName,
 246                       int nLine );
 247 #endif /* _MSC_VER */
 248
 249
 250 #ifdef GC_OPERATOR_NEW_ARRAY
 251
 252 inline void* operator new[](
 253     size_t size,
 254     GCPlacement gcp,
 255     GCCleanUpFunc cleanup = 0,
 256     void* clientData = 0 );
 257     /*
 258     The operator new for arrays, identical to the above. */
 259
 260 #endif /* GC_OPERATOR_NEW_ARRAY */
 261
 262 /****************************************************************************
 263
 264 Inline implementation
 265
 266 ****************************************************************************/
 267
 268 inline void* gc::operator new( size_t size ) {
 269     return GC_MALLOC( size );}
 270
 271 inline void* gc::operator new( size_t size, GCPlacement gcp ) {
 272     if (gcp == UseGC)
 273         return GC_MALLOC( size );
 274     else if (gcp == PointerFreeGC)
 275         return GC_MALLOC_ATOMIC( size );
 276     else
 277         return GC_MALLOC_UNCOLLECTABLE( size );}
 278
 279 inline void* gc::operator new( size_t size, void *p ) {
 280     return p;}
 281
 282 inline void gc::operator delete( void* obj ) {
 283     GC_FREE( obj );}
 284
 285 #ifndef __BORLANDC__
 286   inline void gc::operator delete( void*, void* ) {}
 287 #endif
 288
 289 #ifdef GC_OPERATOR_NEW_ARRAY
 290
 291 inline void* gc::operator new[]( size_t size ) {
 292     return gc::operator new( size );}
 293
 294 inline void* gc::operator new[]( size_t size, GCPlacement gcp ) {
 295     return gc::operator new( size, gcp );}
 296
 297 inline void* gc::operator new[]( size_t size, void *p ) {
 298     return p;}
 299
 300 inline void gc::operator delete[]( void* obj ) {
 301     gc::operator delete( obj );}
 302
 303 #ifndef __BORLANDC__
 304   inline void gc::operator delete[]( void*, void* ) {}
 305 #endif
 306
 307 #endif /* GC_OPERATOR_NEW_ARRAY */
 308
 309
 310 inline gc_cleanup::~gc_cleanup() {
 311     GC_register_finalizer_ignore_self( GC_base(this), 0, 0, 0, 0 );}
 312
 313 inline void gc_cleanup::cleanup( void* obj, void* displ ) {
 314     ((gc_cleanup*) ((char*) obj + (ptrdiff_t) displ))->~gc_cleanup();}
 315
 316 inline gc_cleanup::gc_cleanup() {
 317     GC_finalization_proc oldProc;
 318     void* oldData;
 319     void* base = GC_base( (void *) this );
 320     if (0 != base)  {
 321       // Don't call the debug version, since this is a real base address.
 322       GC_register_finalizer_ignore_self(
 323         base, (GC_finalization_proc)cleanup, (void*) ((char*) this - (char*) base),
 324         &oldProc, &oldData );
 325       if (0 != oldProc) {
 326         GC_register_finalizer_ignore_self( base, oldProc, oldData, 0, 0 );}}}
 327
 328 inline void* operator new(
 329     size_t size,
 330     GCPlacement gcp,
 331     GCCleanUpFunc cleanup,
 332     void* clientData )
 333 {
 334     void* obj;
 335
 336     if (gcp == UseGC) {
 337         obj = GC_MALLOC( size );
 338         if (cleanup != 0)
 339             GC_REGISTER_FINALIZER_IGNORE_SELF(
 340                 obj, cleanup, clientData, 0, 0 );}
 341     else if (gcp == PointerFreeGC) {
 342         obj = GC_MALLOC_ATOMIC( size );}
 343     else {
 344         obj = GC_MALLOC_UNCOLLECTABLE( size );};
 345     return obj;}
 346
 347
 348 #ifdef GC_OPERATOR_NEW_ARRAY
 349
 350 inline void* operator new[](
 351     size_t size,
 352     GCPlacement gcp,
 353     GCCleanUpFunc cleanup,
 354     void* clientData )
 355 {
 356     return ::operator new( size, gcp, cleanup, clientData );}
 357
 358 #endif /* GC_OPERATOR_NEW_ARRAY */
 359
 360
 361 #endif /* GC_CPP_H */
 362