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minor_gc.c

/***********************************************************************/
/*                                                                     */
/*                           Objective Caml                            */
/*                                                                     */
/*             Damien Doligez, projet Para, INRIA Rocquencourt         */
/*                                                                     */
/*  Copyright 1996 Institut National de Recherche en Informatique et   */
/*  en Automatique.  All rights reserved.  This file is distributed    */
/*  under the terms of the GNU Library General Public License, with    */
/*  the special exception on linking described in file ../LICENSE.     */
/*                                                                     */
/***********************************************************************/

/* $Id: minor_gc.c,v 1.42 2004/01/05 20:25:59 doligez Exp $ */

#include <string.h>
#include "config.h"
#include "fail.h"
#include "finalise.h"
#include "gc.h"
#include "gc_ctrl.h"
#include "major_gc.h"
#include "memory.h"
#include "minor_gc.h"
#include "misc.h"
#include "mlvalues.h"
#include "roots.h"
#include "signals.h"

asize_t caml_minor_heap_size;
CAMLexport char *caml_young_start = NULL, *caml_young_end = NULL;
CAMLexport char *caml_young_ptr = NULL, *caml_young_limit = NULL;
static value **ref_table = NULL, **ref_table_end, **ref_table_threshold;
CAMLexport value **caml_ref_table_ptr = NULL, **caml_ref_table_limit;
static asize_t ref_table_size, ref_table_reserve;
int caml_in_minor_collection = 0;

void caml_set_minor_heap_size (asize_t size)
{
  char *new_heap;
  value **new_table;

  Assert (size >= Minor_heap_min);
  Assert (size <= Minor_heap_max);
  Assert (size % sizeof (value) == 0);
  if (caml_young_ptr != caml_young_end) caml_minor_collection ();
                                    Assert (caml_young_ptr == caml_young_end);
  new_heap = (char *) caml_stat_alloc (size);
  if (caml_young_start != NULL){
    caml_stat_free (caml_young_start);
  }
  caml_young_start = new_heap;
  caml_young_end = new_heap + size;
  caml_young_limit = caml_young_start;
  caml_young_ptr = caml_young_end;
  caml_minor_heap_size = size;

  ref_table_size = caml_minor_heap_size / sizeof (value) / 8;
  ref_table_reserve = 256;
  new_table = (value **) caml_stat_alloc ((ref_table_size + ref_table_reserve)
                                          * sizeof (value *));
  if (ref_table != NULL) caml_stat_free (ref_table);
  ref_table = new_table;
  caml_ref_table_ptr = ref_table;
  ref_table_threshold = ref_table + ref_table_size;
  caml_ref_table_limit = ref_table_threshold;
  ref_table_end = ref_table + ref_table_size + ref_table_reserve;
}

static value oldify_todo_list = 0;

/* Note that the tests on the tag depend on the fact that Infix_tag,
   Forward_tag, and No_scan_tag are contiguous. */

void caml_oldify_one (value v, value *p)
{
  value result;
  header_t hd;
  mlsize_t sz, i;
  tag_t tag;

 tail_call:
  if (Is_block (v) && Is_young (v)){
    Assert (Hp_val (v) >= caml_young_ptr);
    hd = Hd_val (v);
    if (hd == 0){         /* If already forwarded */
      *p = Field (v, 0);  /*  then forward pointer is first field. */
    }else{
      tag = Tag_hd (hd);
      if (tag < Infix_tag){
        value field0;

        sz = Wosize_hd (hd);
        result = caml_alloc_shr (sz, tag);
        *p = result;
        field0 = Field (v, 0);
        Hd_val (v) = 0;            /* Set forward flag */
        Field (v, 0) = result;     /*  and forward pointer. */
        if (sz > 1){
          Field (result, 0) = field0;
          Field (result, 1) = oldify_todo_list;    /* Add this block */
          oldify_todo_list = v;                    /*  to the "to do" list. */
        }else{
          Assert (sz == 1);
          p = &Field (result, 0);
          v = field0;
          goto tail_call;
        }
      }else if (tag >= No_scan_tag){
        sz = Wosize_hd (hd);
        result = caml_alloc_shr (sz, tag);
        for (i = 0; i < sz; i++) Field (result, i) = Field (v, i);
        Hd_val (v) = 0;            /* Set forward flag */
        Field (v, 0) = result;     /*  and forward pointer. */
        *p = result;
      }else if (tag == Infix_tag){
        mlsize_t offset = Infix_offset_hd (hd);
        caml_oldify_one (v - offset, p);   /* Cannot recurse deeper than 1. */
        *p += offset;
      }else{
        value f = Forward_val (v);
        tag_t ft = 0;

        Assert (tag == Forward_tag);
        if (Is_block (f) && (Is_young (f) || Is_in_heap (f))){
          ft = Tag_val (Hd_val (f) == 0 ? Field (f, 0) : f);
        }
        if (ft == Forward_tag || ft == Lazy_tag || ft == Double_tag){
          /* Do not short-circuit the pointer.  Copy as a normal block. */
          Assert (Wosize_hd (hd) == 1);
          result = caml_alloc_shr (1, Forward_tag);
          *p = result;
          Hd_val (v) = 0;             /* Set (GC) forward flag */
          Field (v, 0) = result;      /*  and forward pointer. */
          p = &Field (result, 0);
          v = f;
          goto tail_call;
        }else{
          v = f;                        /* Follow the forwarding */
          goto tail_call;               /*  then oldify. */
        }
      }
    }
  }else{
    *p = v;
  }
}

/* Finish the work that was put off by [caml_oldify_one].
   Note that [caml_oldify_one] itself is called by oldify_mopup, so we
   have to be careful to remove the first entry from the list before
   oldifying its fields. */
void caml_oldify_mopup (void)
{
  value v, new_v, f;
  mlsize_t i;

  while (oldify_todo_list != 0){
    v = oldify_todo_list;                /* Get the head. */
    Assert (Hd_val (v) == 0);            /* It must be forwarded. */
    new_v = Field (v, 0);                /* Follow forward pointer. */
    oldify_todo_list = Field (new_v, 1); /* Remove from list. */

    f = Field (new_v, 0);
    if (Is_block (f) && Is_young (f)){
      caml_oldify_one (f, &Field (new_v, 0));
    }
    for (i = 1; i < Wosize_val (new_v); i++){
      f = Field (v, i);
      if (Is_block (f) && Is_young (f)){
        caml_oldify_one (f, &Field (new_v, i));
      }else{
        Field (new_v, i) = f;
      }
    }
  }
}

/* Make sure the minor heap is empty by performing a minor collection
   if needed.
*/
void caml_empty_minor_heap (void)
{
  value **r;

  if (caml_young_ptr != caml_young_end){
    caml_in_minor_collection = 1;
    caml_gc_message (0x02, "<", 0);
    caml_oldify_local_roots();
    for (r = ref_table; r < caml_ref_table_ptr; r++){
      caml_oldify_one (**r, *r);
    }
    caml_oldify_mopup ();
    if (caml_young_ptr < caml_young_start) caml_young_ptr = caml_young_start;
    caml_stat_minor_words += Wsize_bsize (caml_young_end - caml_young_ptr);
    caml_young_ptr = caml_young_end;
    caml_young_limit = caml_young_start;
    caml_ref_table_ptr = ref_table;
    caml_ref_table_limit = ref_table_threshold;
    caml_gc_message (0x02, ">", 0);
    caml_in_minor_collection = 0;
  }
  caml_final_empty_young ();
#ifdef DEBUG
  {
    value *p;
    for (p = (value *) caml_young_start; p < (value *) caml_young_end; ++p){
      *p = Debug_free_minor;
    }
  }
#endif
}

/* Do a minor collection and a slice of major collection, call finalisation
   functions, etc.
   Leave the minor heap empty.
*/
CAMLexport void caml_minor_collection (void)
{
  long prev_alloc_words = caml_allocated_words;

  caml_empty_minor_heap ();

  caml_stat_promoted_words += caml_allocated_words - prev_alloc_words;
  ++ caml_stat_minor_collections;
  caml_major_collection_slice (0);
  caml_force_major_slice = 0;

  caml_final_do_calls ();

  caml_empty_minor_heap ();
}

CAMLexport value caml_check_urgent_gc (value extra_root)
{
  CAMLparam1 (extra_root);
  if (caml_force_major_slice) caml_minor_collection();
  CAMLreturn (extra_root);
}

void caml_realloc_ref_table (void)
{                       Assert (caml_ref_table_ptr == caml_ref_table_limit);
                             Assert (caml_ref_table_limit <= ref_table_end);
                       Assert (caml_ref_table_limit >= ref_table_threshold);

  if (caml_ref_table_limit == ref_table_threshold){
    caml_gc_message (0x08, "ref_table threshold crossed\n", 0);
    caml_ref_table_limit = ref_table_end;
    caml_urge_major_slice ();
  }else{ /* This will almost never happen with the bytecode interpreter. */
    asize_t sz;
    asize_t cur_ptr = caml_ref_table_ptr - ref_table;
                                             Assert (caml_force_major_slice);

    ref_table_size *= 2;
    sz = (ref_table_size + ref_table_reserve) * sizeof (value *);
    caml_gc_message (0x08, "Growing ref_table to %ldk bytes\n", (long) sz/1024);
    ref_table = (value **) realloc ((char *) ref_table, sz);
    if (ref_table == NULL){
      caml_fatal_error ("Fatal error: ref_table overflow\n");
    }
    ref_table_end = ref_table + ref_table_size + ref_table_reserve;
    ref_table_threshold = ref_table + ref_table_size;
    caml_ref_table_ptr = ref_table + cur_ptr;
    caml_ref_table_limit = ref_table_end;
  }
}

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