boehm-gc/include/gc_typed.h

   1 /*
   2  * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
   3  * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
   4  * Copyright 1996 Silicon Graphics.  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
  10  * for any purpose,  provided the above notices are retained on all copies.
  11  * Permission to modify the code and to distribute modified code is granted,
  12  * provided the above notices are retained, and a notice that the code was
  13  * modified is included with the above copyright notice.
  14  */
  15
  16 /*
  17  * Some simple primitives for allocation with explicit type information.
  18  * Facilities for dynamic type inference may be added later.
  19  * Should be used only for extremely performance critical applications,
  20  * or if conservative collector leakage is otherwise a problem (unlikely).
  21  * Note that this is implemented completely separately from the rest
  22  * of the collector, and is not linked in unless referenced.
  23  * This does not currently support GC_DEBUG in any interesting way.
  24  */
  25
  26 #ifndef GC_TYPED_H
  27 #define GC_TYPED_H
  28
  29 #ifndef GC_H
  30 # include "gc.h"
  31 #endif
  32
  33 #ifdef __cplusplus
  34   extern "C" {
  35 #endif
  36
  37 typedef GC_word * GC_bitmap;
  38         /* The least significant bit of the first word is one if        */
  39         /* the first word in the object may be a pointer.               */
  40
  41 #define GC_WORDSZ (8 * sizeof(GC_word))
  42 #define GC_get_bit(bm, index) \
  43             (((bm)[(index) / GC_WORDSZ] >> ((index) % GC_WORDSZ)) & 1)
  44 #define GC_set_bit(bm, index) \
  45             ((bm)[(index) / GC_WORDSZ] |= (GC_word)1 << ((index) % GC_WORDSZ))
  46 #define GC_WORD_OFFSET(t, f) (offsetof(t,f) / sizeof(GC_word))
  47 #define GC_WORD_LEN(t) (sizeof(t) / sizeof(GC_word))
  48 #define GC_BITMAP_SIZE(t) ((GC_WORD_LEN(t) + GC_WORDSZ - 1) / GC_WORDSZ)
  49
  50 typedef GC_word GC_descr;
  51
  52 GC_API GC_descr GC_CALL GC_make_descriptor(const GC_word * /* GC_bitmap bm */,
  53                                            size_t /* len */);
  54                 /* Return a type descriptor for the object whose layout */
  55                 /* is described by the argument.                        */
  56                 /* The least significant bit of the first word is one   */
  57                 /* if the first word in the object may be a pointer.    */
  58                 /* The second argument specifies the number of          */
  59                 /* meaningful bits in the bitmap.  The actual object    */
  60                 /* may be larger (but not smaller).  Any additional     */
  61                 /* words in the object are assumed not to contain       */
  62                 /* pointers.                                            */
  63                 /* Returns a conservative approximation in the          */
  64                 /* (unlikely) case of insufficient memory to build      */
  65                 /* the descriptor.  Calls to GC_make_descriptor         */
  66                 /* may consume some amount of a finite resource.  This  */
  67                 /* is intended to be called once per type, not once     */
  68                 /* per allocation.                                      */
  69
  70 /* It is possible to generate a descriptor for a C type T with  */
  71 /* word aligned pointer fields f1, f2, ... as follows:                  */
  72 /*                                                                      */
  73 /* GC_descr T_descr;                                                    */
  74 /* GC_word T_bitmap[GC_BITMAP_SIZE(T)] = {0};                           */
  75 /* GC_set_bit(T_bitmap, GC_WORD_OFFSET(T,f1));                          */
  76 /* GC_set_bit(T_bitmap, GC_WORD_OFFSET(T,f2));                          */
  77 /* ...                                                                  */
  78 /* T_descr = GC_make_descriptor(T_bitmap, GC_WORD_LEN(T));              */
  79
  80 GC_API GC_ATTR_MALLOC GC_ATTR_ALLOC_SIZE(1) void * GC_CALL
  81         GC_malloc_explicitly_typed(size_t /* size_in_bytes */,
  82                                    GC_descr /* d */);
  83                 /* Allocate an object whose layout is described by d.   */
  84                 /* The resulting object MAY NOT BE PASSED TO REALLOC.   */
  85                 /* The returned object is cleared.                      */
  86
  87 GC_API GC_ATTR_MALLOC GC_ATTR_ALLOC_SIZE(1) void * GC_CALL
  88         GC_malloc_explicitly_typed_ignore_off_page(size_t /* size_in_bytes */,
  89                                                    GC_descr /* d */);
  90
  91 GC_API GC_ATTR_MALLOC void * GC_CALL
  92         GC_calloc_explicitly_typed(size_t /* nelements */,
  93                                    size_t /* element_size_in_bytes */,
  94                                    GC_descr /* d */);
  95         /* Allocate an array of nelements elements, each of the */
  96         /* given size, and with the given descriptor.           */
  97         /* The element size must be a multiple of the byte      */
  98         /* alignment required for pointers.  E.g. on a 32-bit   */
  99         /* machine with 16-bit aligned pointers, size_in_bytes  */
 100         /* must be a multiple of 2.                             */
 101         /* Returned object is cleared.                          */
 102
 103 #ifdef GC_DEBUG
 104 # define GC_MALLOC_EXPLICITLY_TYPED(bytes, d) GC_MALLOC(bytes)
 105 # define GC_CALLOC_EXPLICITLY_TYPED(n, bytes, d) GC_MALLOC((n) * (bytes))
 106 #else
 107 # define GC_MALLOC_EXPLICITLY_TYPED(bytes, d) \
 108                         GC_malloc_explicitly_typed(bytes, d)
 109 # define GC_CALLOC_EXPLICITLY_TYPED(n, bytes, d) \
 110                         GC_calloc_explicitly_typed(n, bytes, d)
 111 #endif
 112
 113 #ifdef __cplusplus
 114   } /* matches extern "C" */
 115 #endif
 116
 117 #endif /* GC_TYPED_H */