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