Re: MPS: weak hash tables

[Eli Zaretskii <eliz@gnu.org>]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Cc: pipcet@protonmail.com,  eller.helmut@gmail.com,  yantar92@posteo.net,
>   emacs-devel@gnu.org
> Date: Sun, 07 Jul 2024 20:15:34 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I understand all that, but unchaining an interval involves the need to
> > modify the pointers of its adjacent nodes, and how can MPS do that
> > without understanding our data structures?
> 
> Can you please show me what code you mean? 

This one:

  static void
  sweep_intervals (void)
  {
    struct interval_block **iprev = &interval_block;
    int lim = interval_block_index;
    object_ct num_free = 0, num_used = 0;

    interval_free_list = 0;

    for (struct interval_block *iblk; (iblk = *iprev); )
      {
	int this_free = 0;
	ASAN_UNPOISON_INTERVAL_BLOCK (iblk);
	for (int i = 0; i < lim; i++)
	  {
	    if (!iblk->intervals[i].gcmarkbit)
	      {
		set_interval_parent (&iblk->intervals[i], interval_free_list);
		interval_free_list = &iblk->intervals[i];
		ASAN_POISON_INTERVAL (&iblk->intervals[i]);
		this_free++;
	      }
	    else
	      {
		num_used++;
		iblk->intervals[i].gcmarkbit = 0;
	      }
	  }
	lim = INTERVAL_BLOCK_SIZE;
	/* If this block contains only free intervals and we have already
	   seen more than two blocks worth of free intervals then
	   deallocate this block.  */
	if (this_free == INTERVAL_BLOCK_SIZE && num_free > INTERVAL_BLOCK_SIZE)
	  {
	    *iprev = iblk->next;
	    /* Unhook from the free list.  */
	    ASAN_UNPOISON_INTERVAL (&iblk->intervals[0]);
	    interval_free_list = INTERVAL_PARENT (&iblk->intervals[0]);
	    lisp_free (iblk);
	  }
	else
	  {
	    num_free += this_free;
	    iprev = &iblk->next;
	  }
      }