251 lines
8.1 KiB
C
251 lines
8.1 KiB
C
/***********************************************************************/
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/* */
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/* Objective Caml */
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/* */
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/* Damien Doligez, projet Para, INRIA Rocquencourt */
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/* */
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/* Copyright 1996 Institut National de Recherche en Informatique et */
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/* Automatique. Distributed only by permission. */
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/* */
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/***********************************************************************/
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/* $Id$ */
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#include "config.h"
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#include "freelist.h"
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#include "gc.h"
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#include "gc_ctrl.h"
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#include "major_gc.h"
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#include "misc.h"
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#include "mlvalues.h"
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/* The free-list is kept sorted by increasing addresses.
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This makes the merging of adjacent free blocks possible.
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(See [fl_merge_block].)
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*/
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typedef struct {
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char *next_bp; /* Pointer to the first byte of the next block. */
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} block;
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/* The sentinel can be located anywhere in memory, but it must not be
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adjacent to any heap object. */
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static struct {
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value filler1; /* Make sure the sentinel is never adjacent to any block. */
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header_t h;
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value first_bp;
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value filler2; /* Make sure the sentinel is never adjacent to any block. */
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} sentinel = {0, Make_header (0, 0, Blue), 0, 0};
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#define Fl_head ((char *) (&(sentinel.first_bp)))
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static char *fl_prev = Fl_head; /* Current allocation pointer. */
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static char *fl_last = NULL; /* Last block in the list. Only valid
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just after fl_allocate returned NULL. */
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char *fl_merge = Fl_head; /* Current insertion pointer. Managed
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jointly with [sweep_slice]. */
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#define Next(b) (((block *) (b))->next_bp)
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#ifdef DEBUG
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void fl_check ()
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{
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char *cur, *prev;
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int prev_found = 0, merge_found = 0;
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prev = Fl_head;
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cur = Next (prev);
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while (cur != NULL){
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Assert (Is_in_heap (cur));
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if (cur == fl_prev) prev_found = 1;
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if (cur == fl_merge) merge_found = 1;
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prev = cur;
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cur = Next (prev);
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}
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Assert (prev_found || fl_prev == Fl_head);
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Assert (merge_found || fl_merge == Fl_head);
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}
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#endif
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/* [allocate_block] is called by [fl_allocate]. Given a suitable free
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block and the desired size, it allocates a new block from the free
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block. There are three cases:
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0. The free block has the desired size. Detach the block from the
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free-list and return it.
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1. The free block is 1 word longer than the desired size. Detach
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the block from the free list. The remaining word cannot be linked:
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turn it into an empty block (header only), and return the rest.
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2. The free block is big enough. Split it in two and return the right
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block.
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In all cases, the allocated block is right-justified in the free block:
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it is located in the high-address words of the free block. This way,
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the linking of the free-list does not change in case 2.
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*/
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static char *allocate_block (wh_sz, prev, cur)
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mlsize_t wh_sz;
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char *prev, *cur;
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{
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header_t h = Hd_bp (cur);
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Assert (Whsize_hd (h) >= wh_sz);
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if (Wosize_hd (h) < wh_sz + 1){ /* Cases 0 and 1. */
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Next (prev) = Next (cur);
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Assert (Is_in_heap (Next (prev)) || Next (prev) == NULL);
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if (fl_merge == cur) fl_merge = prev;
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#ifdef DEBUG
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fl_last = NULL;
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#endif
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/* In case 1, the following creates the empty block correctly.
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In case 0, it gives an invalid header to the block. The function
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calling [fl_allocate] will overwrite it. */
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Hd_op (cur) = Make_header (0, 0, White);
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}else{ /* Case 2. */
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Hd_op (cur) = Make_header (Wosize_hd (h) - wh_sz, 0, Blue);
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}
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fl_prev = prev;
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return cur + Bosize_hd (h) - Bsize_wsize (wh_sz);
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}
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/* [fl_allocate] does not set the header of the newly allocated block.
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The calling function must do it before any GC function gets called.
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[fl_allocate] returns a head pointer.
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*/
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char *fl_allocate (wo_sz)
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mlsize_t wo_sz;
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{
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char *cur, *prev;
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Assert (sizeof (char *) == sizeof (value));
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Assert (fl_prev != NULL);
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Assert (wo_sz >= 1);
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/* Search from [fl_prev] to the end of the list. */
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prev = fl_prev;
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cur = Next (prev);
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while (cur != NULL){ Assert (Is_in_heap (cur));
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if (Wosize_bp (cur) >= wo_sz){
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return allocate_block (Whsize_wosize (wo_sz), prev, cur);
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}
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prev = cur;
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cur = Next (prev);
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}
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fl_last = prev;
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/* Search from the start of the list to [fl_prev]. */
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prev = Fl_head;
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cur = Next (prev);
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while (prev != fl_prev){
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if (Wosize_bp (cur) >= wo_sz){
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return allocate_block (Whsize_wosize (wo_sz), prev, cur);
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}
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prev = cur;
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cur = Next (prev);
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}
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/* No suitable block was found. */
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return NULL;
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}
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void fl_init_merge ()
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{
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fl_merge = Fl_head;
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#ifdef DEBUG
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fl_check ();
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#endif
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}
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/* [fl_merge_block] returns the head pointer of the next block after [bp],
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because merging blocks may change the size of [bp]. */
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char *fl_merge_block (bp)
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char *bp;
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{
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char *prev, *cur, *adj;
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header_t hd = Hd_bp (bp);
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#ifdef DEBUG
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{
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mlsize_t i;
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for (i = 0; i < Wosize_hd (hd); i++){
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Field (Val_bp (bp), i) = not_random ();
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}
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}
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#endif
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prev = fl_merge;
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cur = Next (prev);
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/* The sweep code makes sure that this is the right place to insert
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this block: */
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Assert (prev < bp || prev == Fl_head);
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Assert (cur > bp || cur == NULL);
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/* If [bp] and [cur] are adjacent, remove [cur] from the free-list
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and merge them. */
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adj = bp + Bosize_hd (hd);
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if (adj == Hp_bp (cur)){
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char *next_cur = Next (cur);
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long cur_whsz = Whsize_bp (cur);
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Next (prev) = next_cur;
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if (fl_prev == cur) fl_prev = prev;
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hd = Make_header (Wosize_hd (hd) + cur_whsz, 0, Blue);
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Hd_bp (bp) = hd;
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adj = bp + Bosize_hd (hd);
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#ifdef DEBUG
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fl_last = NULL;
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Next (cur) = (char *) not_random ();
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Hd_bp (cur) = not_random ();
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#endif
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cur = next_cur;
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}
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/* If [prev] and [bp] are adjacent merge them, else insert [bp] into
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the free-list if it is big enough. */
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if (prev + Bosize_bp (prev) == Hp_bp (bp)){
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Hd_bp (prev) = Make_header (Wosize_bp (prev) + Whsize_hd (hd), 0, Blue);
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#ifdef DEBUG
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Hd_bp (bp) = not_random ();
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#endif
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Assert (fl_merge == prev);
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}else if (Wosize_hd (hd) != 0){
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Hd_bp (bp) = Bluehd_hd (hd);
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Next (bp) = cur;
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Next (prev) = bp;
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fl_merge = bp;
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} /* Else leave it in white. */
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return adj;
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}
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/* This is a heap extension. We have to insert it in the right place
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in the free-list.
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[fl_add_block] can only be called just after a call to [fl_allocate]
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that returned NULL.
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Most of the heap extensions are expected to be at the end of the
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free list. (This depends on the implementation of [malloc].)
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*/
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void fl_add_block (bp)
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char *bp;
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{
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Assert (fl_last != NULL);
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Assert (Next (fl_last) == NULL);
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#ifdef DEBUG
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{
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mlsize_t i;
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for (i = 0; i < Wosize_bp (bp); i++){
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Field (Val_bp (bp), i) = not_random ();
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}
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}
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#endif
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if (bp > fl_last){
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Next (fl_last) = bp;
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Next (bp) = NULL;
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}else{
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char *cur, *prev;
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prev = Fl_head;
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cur = Next (prev);
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while (cur != NULL && cur < bp){ Assert (prev < bp || prev == Fl_head);
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prev = cur;
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cur = Next (prev);
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} Assert (prev < bp || prev == Fl_head);
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Assert (cur > bp || cur == NULL);
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Next (bp) = cur;
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Next (prev) = bp;
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/* When inserting a block between fl_merge and gc_sweep_hp, we must
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advance fl_merge to the new block, so that fl_merge is always the
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last free-list block before gc_sweep_hp. */
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if (prev == fl_merge && bp <= gc_sweep_hp) fl_merge = bp;
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}
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}
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