runtime/gc/weak.h

   1 /* Copyright (C) 1999-2007 Henry Cejtin, Matthew Fluet, Suresh
   2  *    Jagannathan, and Stephen Weeks.
   3  * Copyright (C) 1997-2000 NEC Research Institute.
   4  *
   5  * MLton is released under a BSD-style license.
   6  * See the file MLton-LICENSE for details.
   7  */
   8
   9 #if (defined (MLTON_GC_INTERNAL_TYPES))
  10
  11 /*
  12  * Weak objects have the following layout:
  13  *
  14  * header ::
  15  * padding ::
  16  * link (native-pointer) ::
  17  * objptr (object-pointer)
  18  *
  19  * The object type indexed by the header determines whether the weak
  20  * is valid or not.  If the type has numObjptrs == 1, then the weak
  21  * pointer is valid.  Otherwise, the type has numObjptrs == 0 and the
  22  * weak pointer is not valid.
  23  *
  24  * There may be zero or more bytes of padding for alignment purposes.
  25  *
  26  * The link native-pointer is used to chain the live weaks together
  27  * during a copying/mark-compact gc and is otherwise unused.
  28  *
  29  * The final component is the weak object-pointer.
  30  *
  31  * Note that the order of the fields is important.  The non-objptr
  32  * field must be first, because a weak object is sometimes treated as
  33  * a normal object.
  34  */
  35 typedef struct GC_weak {
  36   struct GC_weak *link;
  37   objptr objptr;
  38 } __attribute__ ((packed)) *GC_weak;
  39
  40 COMPILE_TIME_ASSERT(GC_weak__packed,
  41                     sizeof(struct GC_weak) ==
  42                     sizeof(struct GC_weak*)
  43                     + sizeof(objptr));
  44
  45 #endif /* (defined (MLTON_GC_INTERNAL_TYPES)) */
  46
  47 #if (defined (MLTON_GC_INTERNAL_FUNCS))
  48
  49 static inline size_t sizeofWeak (GC_state s);
  50 static inline size_t offsetofWeak (GC_state s);
  51
  52 #endif /* (defined (MLTON_GC_INTERNAL_FUNCS)) */
  53
  54 #if (defined (MLTON_GC_INTERNAL_BASIS))
  55
  56 PRIVATE uint32_t GC_weakCanGet (GC_state s, pointer p);
  57 PRIVATE pointer GC_weakGet (GC_state s, pointer p);
  58 PRIVATE pointer GC_weakNew (GC_state s, GC_header header, pointer p);
  59
  60 #endif /* (defined (MLTON_GC_INTERNAL_BASIS)) */