guile/libguile/private-gc.h

/*
  (c) FSF 2002. 
*/
   

#ifndef PRIVATE_GC
#define PRIVATE_GC

#include  "_scm.h"

/* {heap tuning parameters}
 *
 * These are parameters for controlling memory allocation.  The heap
 * is the area out of which scm_cons, and object headers are allocated.
 *
 * Each heap cell is 8 bytes on a 32 bit machine and 16 bytes on a
 * 64 bit machine.  The units of the _SIZE parameters are bytes.
 * Cons pairs and object headers occupy one heap cell.
 *
 * SCM_INIT_HEAP_SIZE is the initial size of heap.  If this much heap is
 * allocated initially the heap will grow by half its current size
 * each subsequent time more heap is needed.
 *
 * If SCM_INIT_HEAP_SIZE heap cannot be allocated initially, SCM_HEAP_SEG_SIZE
 * will be used, and the heap will grow by SCM_HEAP_SEG_SIZE when more
 * heap is needed.  SCM_HEAP_SEG_SIZE must fit into type size_t.  This code
 * is in scm_init_storage() and alloc_some_heap() in sys.c
 *
 * If SCM_INIT_HEAP_SIZE can be allocated initially, the heap will grow by
 * SCM_EXPHEAP(scm_heap_size) when more heap is needed.
 *
 * SCM_MIN_HEAP_SEG_SIZE is minimum size of heap to accept when more heap
 * is needed.
 */


/*
 * Heap size 45000 and 40% min yield gives quick startup and no extra
 * heap allocation.  Having higher values on min yield may lead to
 * large heaps, especially if code behaviour is varying its
 * maximum consumption between different freelists.
 */

/*
  These values used to be global C variables. However, they're also
  available through the environment, and having a double interface is
  confusing. Now they're #defines --hwn.
 */

#define SCM_DEFAULT_INIT_HEAP_SIZE_1  256*1024
#define SCM_DEFAULT_MIN_YIELD_1 40
#define SCM_DEFAULT_INIT_HEAP_SIZE_2 32*1024

/* The following value may seem large, but note that if we get to GC at
 * all, this means that we have a numerically intensive application
 */
#define SCM_DEFAULT_MIN_YIELD_2 40

#define SCM_DEFAULT_MAX_SEGMENT_SIZE  (20*1024*1024L)



#define SCM_MIN_HEAP_SEG_SIZE (8 * SCM_GC_SIZEOF_CARD)
#define SCM_HEAP_SEG_SIZE (16384L * sizeof (scm_t_cell))


#define SCM_DOUBLECELL_ALIGNED_P(x)  (((2 * sizeof (scm_t_cell) - 1) & SCM_UNPACK (x)) == 0)


#define SCM_GC_CARD_BVEC_SIZE_IN_LONGS \
    ((SCM_GC_CARD_N_CELLS + SCM_C_BVEC_LONG_BITS - 1) / SCM_C_BVEC_LONG_BITS)
#define SCM_GC_IN_CARD_HEADERP(x) \
  (scm_t_cell *) (x) <  SCM_GC_CELL_CARD (x) + SCM_GC_CARD_N_HEADER_CELLS


int scm_getenv_int (const char *var, int def);


typedef enum { return_on_error, abort_on_error } policy_on_error;

/* gc-freelist*/

/*
  FREELIST:

  A struct holding GC statistics on a particular type of cells.
*/
typedef struct scm_t_cell_type_statistics {

  /*
    heap segment where the last cell was allocated 
  */
  int heap_segment_idx;

  /* minimum yield on this list in order not to grow the heap
   */
  long min_yield;

  /* defines min_yield as percent of total heap size
   */
  int min_yield_fraction;
  
  /* number of cells per object on this list */
  int span;

  /* number of collected cells during last GC */
  unsigned long collected;

  /* number of collected cells during penultimate GC */
  unsigned long collected_1;

  /* total number of cells in heap segments
   * belonging to this list.
   */
  unsigned long heap_size;

  
} scm_t_cell_type_statistics;


extern scm_t_cell_type_statistics scm_i_master_freelist;
extern scm_t_cell_type_statistics scm_i_master_freelist2;
extern unsigned long scm_gc_cells_collected_1;

void scm_i_adjust_min_yield (scm_t_cell_type_statistics *freelist);
void scm_i_gc_sweep_freelist_reset (scm_t_cell_type_statistics *freelist);
int scm_i_gc_grow_heap_p (scm_t_cell_type_statistics * freelist);


#define SCM_HEAP_SIZE \
  (scm_i_master_freelist.heap_size + scm_i_master_freelist2.heap_size)


#define SCM_MAX(A, B) ((A) > (B) ? (A) : (B))
#define SCM_MIN(A, B) ((A) < (B) ? (A) : (B))

/* CELL_P checks a random word whether it has the right form for a
   pointer to a cell.  Use scm_i_find_heap_segment_containing_object
   to find out whether it actually points to a real cell.

   The right form for a cell pointer is this: the low three bits must
   be scm_tc3_cons, and when the scm_tc3_cons tag is stripped, the
   resulting pointer must be correctly aligned.
   scm_i_initialize_heap_segment_data guarantees that the test below
   works.
*/
#define CELL_P(x)  ((SCM_UNPACK(x) & (sizeof(scm_t_cell)-1)) == scm_tc3_cons)

/*
  gc-mark
 */


void scm_mark_all (void);



/*
gc-segment:
*/




/*

 Cells are stored in a heap-segment: it is a contiguous chunk of
 memory, that associated with one freelist. 
*/

typedef struct scm_t_heap_segment
{
  /*
    {lower, upper} bounds of the segment

    The upper bound is also the start of the mark space.
  */
  scm_t_cell *bounds[2];

  /*
    If we ever decide to give it back, we could do it with this ptr.

    Note that giving back memory is not very useful; as long we don't
    touch a chunk of memory, the virtual memory system will keep it
    swapped out. We could simply forget about a block.

    (not that we do that, but anyway.) 
   */

  void* malloced;

  scm_t_cell * next_free_card;
  
  /* address of the head-of-freelist pointer for this segment's cells.
     All segments usually point to the same one, scm_i_freelist.  */
  scm_t_cell_type_statistics *freelist;
  
  /* number of cells per object in this segment */
  int span;


  /*
    Is this the first time that the cells are accessed? 
   */
  int first_time;
  
} scm_t_heap_segment;



/*

  A table of segment records is kept that records the upper and
  lower extents of the segment;  this is used during the conservative
  phase of gc to identify probably gc roots (because they point
  into valid segments at reasonable offsets).

*/
extern scm_t_heap_segment ** scm_i_heap_segment_table;
extern size_t scm_i_heap_segment_table_size;


int scm_i_init_card_freelist (scm_t_cell * card, SCM *free_list,scm_t_heap_segment*);
int scm_i_sweep_card (scm_t_cell * card, SCM *free_list, scm_t_heap_segment*);
void scm_i_card_statistics (scm_t_cell *p, SCM hashtab, scm_t_heap_segment *seg);
char const *scm_i_tag_name (scm_t_bits tag); /* MOVEME */

int scm_i_initialize_heap_segment_data (scm_t_heap_segment * segment, size_t requested);
int scm_i_segment_card_count (scm_t_heap_segment * seg);
int scm_i_segment_cell_count (scm_t_heap_segment * seg);

void scm_i_clear_segment_mark_space (scm_t_heap_segment *seg);
scm_t_heap_segment * scm_i_make_empty_heap_segment (scm_t_cell_type_statistics*);
SCM scm_i_sweep_some_cards (scm_t_heap_segment *seg);
void scm_i_sweep_segment (scm_t_heap_segment * seg);

void scm_i_heap_segment_statistics (scm_t_heap_segment *seg, SCM tab);

     
int scm_i_insert_segment (scm_t_heap_segment * seg);
long int scm_i_find_heap_segment_containing_object (SCM obj);
int scm_i_get_new_heap_segment (scm_t_cell_type_statistics *, policy_on_error);
void scm_i_clear_mark_space (void);
void scm_i_sweep_segments (void);
SCM scm_i_sweep_some_segments (scm_t_cell_type_statistics * fl);
void scm_i_reset_segments (void);
void scm_i_sweep_all_segments (char const *reason);
SCM scm_i_all_segments_statistics (SCM hashtab);
void scm_i_make_initial_segment (int init_heap_size, scm_t_cell_type_statistics *freelist);

extern long int scm_i_deprecated_memory_return;


/*
  global init funcs.
 */
void scm_gc_init_malloc (void);
void scm_gc_init_freelist (void);
void scm_gc_init_segments (void);
void scm_gc_init_mark (void);


#endif