path: root/src/ralloc.c

/* Block-relocating memory allocator. 
   Copyright (C) 1993 Free Software Foundation, Inc.

This file is part of GNU Emacs.

GNU Emacs is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 1, or (at your option)
any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs; see the file COPYING.  If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */

/* NOTES:

   Only relocate the blocs necessary for SIZE in r_alloc_sbrk,
   rather than all of them.  This means allowing for a possible
   hole between the first bloc and the end of malloc storage. */

#ifdef emacs

#include <config.h>
#include "lisp.h"		/* Needed for VALBITS.  */

#undef NULL

/* The important properties of this type are that 1) it's a pointer, and
   2) arithmetic on it should work as if the size of the object pointed
   to has a size of 1.  */
#if 0 /* Arithmetic on void* is a GCC extension.  */
#ifdef __STDC__
typedef void *POINTER;
#else

#ifdef	HAVE_CONFIG_H
#include "config.h"
#endif

typedef char *POINTER;

#endif
#endif /* 0 */

/* Unconditionally use char * for this.  */
typedef char *POINTER;

typedef unsigned long SIZE;

/* Declared in dispnew.c, this version doesn't screw up if regions
   overlap.  */
extern void safe_bcopy ();

#include "getpagesize.h"

#else	/* Not emacs.  */

#include <stddef.h>

typedef size_t SIZE;
typedef void *POINTER;

#include <unistd.h>
#include <malloc.h>
#include <string.h>

#define safe_bcopy(x, y, z) memmove (y, x, z)

#endif	/* emacs.  */

#define NIL ((POINTER) 0)

/* A flag to indicate whether we have initialized ralloc yet.  For
   Emacs's sake, please do not make this local to malloc_init; on some
   machines, the dumping procedure makes all static variables
   read-only.  On these machines, the word static is #defined to be
   the empty string, meaning that r_alloc_initialized becomes an
   automatic variable, and loses its value each time Emacs is started up.  */
static int r_alloc_initialized = 0;

static void r_alloc_init ();

/* Declarations for working with the malloc, ralloc, and system breaks.  */

/* Function to set the real break value. */
static POINTER (*real_morecore) ();

/* The break value, as seen by malloc (). */
static POINTER virtual_break_value;

/* The break value, viewed by the relocatable blocs. */
static POINTER break_value;

/* This is the size of a page.  We round memory requests to this boundary.  */
static int page_size;

/* Whenever we get memory from the system, get this many extra bytes.  This 
   must be a multiple of page_size.  */
static int extra_bytes;

/* Macros for rounding.  Note that rounding to any value is possible
   by changing the definition of PAGE. */
#define PAGE (getpagesize ())
#define ALIGNED(addr) (((unsigned long int) (addr) & (page_size - 1)) == 0)
#define ROUNDUP(size) (((unsigned long int) (size) + page_size - 1) \
		       & ~(page_size - 1))
#define ROUND_TO_PAGE(addr) (addr & (~(page_size - 1)))

#define MEM_ALIGN sizeof(double)
#define MEM_ROUNDUP(addr) (((unsigned long int)(addr) + MEM_ALIGN - 1) \
				   & ~(MEM_ALIGN - 1))

/* Data structures of heaps and blocs */
typedef struct heap
{
  struct heap *next;
  struct heap *prev;
  POINTER start;
  POINTER end;
  POINTER bloc_start;		/* start of relocatable blocs */
} *heap_ptr;

#define NIL_HEAP ((heap_ptr) 0)
#define HEAP_PTR_SIZE (sizeof (struct heap))

/* Head and tail of the list of heaps. */
static heap_ptr first_heap, last_heap;

/* These structures are allocated in the malloc arena.
   The linked list is kept in order of increasing '.data' members.
   The data blocks abut each other; if b->next is non-nil, then
   b->data + b->size == b->next->data.  */
typedef struct bp
{
  struct bp *next;
  struct bp *prev;
  POINTER *variable;
  POINTER data;
  SIZE size;
  POINTER new_data;		/* tmporarily used for relocation */
} *bloc_ptr;

#define NIL_BLOC ((bloc_ptr) 0)
#define BLOC_PTR_SIZE (sizeof (struct bp))

/* Head and tail of the list of relocatable blocs. */
static bloc_ptr first_bloc, last_bloc;


/* Functions to get and return memory from the system.  */

/* Obtain SIZE bytes of space starting at ADDRESS in a heap.
   If enough space is not presently available in our reserve, this means
   getting more page-aligned space from the system. If the retuned space
   is not contiguos to the last heap, allocate a new heap, and append it
   to the heap list.

   Return the address of the space if all went well, or zero if we couldn't
   allocate the memory.  */
static POINTER
obtain (address, size)
    POINTER address;
    SIZE size;
{
  heap_ptr heap;
  SIZE already_available;

  for (heap = last_heap; heap; heap = heap->prev)
    {
      if (heap->start <= address && address <= heap->end)
	break;
    }

  if (! heap)
    abort();

  while (heap && address + size > heap->end)
    {
      heap = heap->next;
      if (heap == NIL_HEAP)
	break;
      address = heap->bloc_start;
    }

  if (heap == NIL_HEAP)
    {
      POINTER new = (*real_morecore)(0);
      SIZE get;

      already_available = (char *)last_heap->end - (char *)address;

      if (new != last_heap->end)
	{
	  /* Someone else called sbrk(). */
	  heap_ptr new_heap = (heap_ptr) MEM_ROUNDUP(new);
	  POINTER bloc_start = (POINTER) MEM_ROUNDUP((POINTER)(new_heap + 1));

	  if ((*real_morecore) (bloc_start - new) != new)
	    return 0;

	  new_heap->start = new;
	  new_heap->end = bloc_start;
	  new_heap->bloc_start = bloc_start;
	  new_heap->next = NIL_HEAP;
	  new_heap->prev = last_heap;
	  last_heap->next = new_heap;
	  last_heap = new_heap;

	  address = bloc_start;
	  already_available = 0;
	}

      /* Get some extra, so we can come here less often.  */
      get = size + extra_bytes - already_available;
      get = (char *) ROUNDUP((char *)last_heap->end + get)
	- (char *) last_heap->end;

      if ((*real_morecore) (get) != last_heap->end)
	return 0;

      last_heap->end += get;
    }

  return address;
}

/* If the last heap has a excessive space, return it to the system. */
static void
relinquish ()
{
  register heap_ptr h;
  int excess = 0;

  for (h = last_heap; h && break_value < h->end; h = h->prev)
    {
      excess += (char *) h->end - (char *) ((break_value < h->bloc_start)
					    ? h->bloc_start : break_value);
    }

  if (excess > extra_bytes * 2 && (*real_morecore) (0) == last_heap->end)
    {
      /* Keep extra_bytes worth of empty space.
	 And don't free anything unless we can free at least extra_bytes.  */
      excess -= extra_bytes;

      if ((char *)last_heap->end - (char *)last_heap->bloc_start <= excess)
	{
	  /* Return the last heap with its header to the system */
	  excess = (char *)last_heap->end - (char *)last_heap->start;
	  last_heap = last_heap->prev;
	  last_heap->next = NIL_HEAP;
	}
      else
	{
	  excess = (char *) last_heap->end
			- (char *) ROUNDUP((char *)last_heap->end - excess);
	  last_heap->end -= excess;
	}

      if ((*real_morecore) (- excess) == 0)
	abort ();
    }
}

/* The meat - allocating, freeing, and relocating blocs.  */

/* Find the bloc referenced by the address in PTR.  Returns a pointer
   to that block. */

static bloc_ptr
find_bloc (ptr)
     POINTER *ptr;
{
  register bloc_ptr p = first_bloc;

  while (p != NIL_BLOC)
    {
      if (p->variable == ptr && p->data == *ptr)
	return p;

      p = p->next;
    }

  return p;
}

/* Allocate a bloc of SIZE bytes and append it to the chain of blocs.
   Returns a pointer to the new bloc, or zero if we couldn't allocate
   memory for the new block.  */

static bloc_ptr
get_bloc (size)
     SIZE size;
{
  register bloc_ptr new_bloc;

  if (! (new_bloc = (bloc_ptr) malloc (BLOC_PTR_SIZE))
      || ! (new_bloc->data = obtain (break_value, size)))
    {
      if (new_bloc)
	free (new_bloc);

      return 0;
    }

  break_value = new_bloc->data + size;

  new_bloc->size = size;
  new_bloc->next = NIL_BLOC;
  new_bloc->variable = (POINTER *) NIL;
  new_bloc->new_data = 0;

  if (first_bloc)
    {
      new_bloc->prev = last_bloc;
      last_bloc->next = new_bloc;
      last_bloc = new_bloc;
    }
  else
    {
      first_bloc = last_bloc = new_bloc;
      new_bloc->prev = NIL_BLOC;
    }

  return new_bloc;
}

/* Calculate new locations of blocs in the list begining with BLOC,
   whose spaces is started at ADDRESS in HEAP.  If enough space is
   not presently available in our reserve, obtain() is called for
   more space. 
   
   Do not touch the contents of blocs or break_value. */

static int
relocate_blocs (bloc, heap, address)
    bloc_ptr bloc;
    heap_ptr heap;
    POINTER address;
{
  register bloc_ptr b = bloc;

  while (b)
    {
      while (heap && address + b->size > heap->end)
	{
	  heap = heap->next;
	  if (heap == NIL_HEAP)
	    break;
	  address = heap->bloc_start;
	}

      if (heap == NIL_HEAP)
	{
	  register bloc_ptr tb = b;
	  register SIZE s = 0;

	  while (tb != NIL_BLOC)
	    {
	      s += tb->size;
	      tb = tb->next;
	    }

	  if (! (address = obtain(address, s)))
	    return 0;

	  heap = last_heap;
	}

      b->new_data = address;
      address += b->size;
      b = b->next;
    }

  return 1;
}

/* Resize BLOC to SIZE bytes. */
static int
resize_bloc (bloc, size)
    bloc_ptr bloc;
    SIZE size;
{
  register bloc_ptr b;
  heap_ptr heap;
  POINTER address;
  SIZE old_size;

  if (bloc == NIL_BLOC || size == bloc->size)
    return 1;

  for (heap = first_heap; heap != NIL_HEAP; heap = heap->next)
    {
      if (heap->bloc_start <= bloc->data && bloc->data <= heap->end)
	break;
    }

  if (heap == NIL_HEAP)
    abort();

  old_size = bloc->size;
  bloc->size = size;

  /* Note that bloc could be moved into the previous heap. */
  address = bloc->prev ? bloc->prev->data + bloc->prev->size
			  : first_heap->bloc_start;
  while (heap)
    {
      if (heap->bloc_start <= address && address <= heap->end)
	break;
      heap = heap->prev;
    }

  if (! relocate_blocs (bloc, heap, address))
    {
      bloc->size = old_size;
      return 0;
    }

  if (size > old_size)
    {
      for (b = last_bloc; b != bloc; b = b->prev)
	{
	  safe_bcopy (b->data, b->new_data, b->size);
	  *b->variable = b->data = b->new_data;
	}
      safe_bcopy (bloc->data, bloc->new_data, old_size);
      bzero (bloc->new_data + old_size, size - old_size);
      *bloc->variable = bloc->data = bloc->new_data;
    }
  else
    {
      for (b = bloc; b != NIL_BLOC; b = b->next)
	{
	  safe_bcopy (b->data, b->new_data, b->size);
	  *b->variable = b->data = b->new_data;
	}
    }

  break_value = last_bloc ? last_bloc->data + last_bloc->size
		    : first_heap->bloc_start;
  return 1;
}

/* Free BLOC from the chain of blocs, relocating any blocs above it
   and returning BLOC->size bytes to the free area. */

static void
free_bloc (bloc)
     bloc_ptr bloc;
{
  resize_bloc (bloc, 0);

  if (bloc == first_bloc && bloc == last_bloc)
    {
      first_bloc = last_bloc = NIL_BLOC;
    }
  else if (bloc == last_bloc)
    {
      last_bloc = bloc->prev;
      last_bloc->next = NIL_BLOC;
    }
  else if (bloc == first_bloc)
    {
      first_bloc = bloc->next;
      first_bloc->prev = NIL_BLOC;
    }
  else
    {
      bloc->next->prev = bloc->prev;
      bloc->prev->next = bloc->next;
    }

  relinquish ();
  free (bloc);
}

/* Interface routines.  */

static int use_relocatable_buffers;
static int r_alloc_freeze_level;

/* Obtain SIZE bytes of storage from the free pool, or the system, as
   necessary.  If relocatable blocs are in use, this means relocating
   them.  This function gets plugged into the GNU malloc's __morecore
   hook.

   We provide hysteresis, never relocating by less than extra_bytes.

   If we're out of memory, we should return zero, to imitate the other
   __morecore hook values - in particular, __default_morecore in the
   GNU malloc package.  */

POINTER 
r_alloc_sbrk (size)
     long size;
{
  register bloc_ptr b;
  POINTER address;

  if (! use_relocatable_buffers)
    return (*real_morecore) (size);

  if (size == 0)
    return virtual_break_value;

  if (size > 0)
    {
      /* Allocate a page-aligned space. GNU malloc would reclaim an
	 extra space if we passed an unaligned one. But we could
	 not always find a space which is contiguos to the previous. */
      POINTER new_bloc_start;
      heap_ptr h = first_heap;
      SIZE get = ROUNDUP(size);

      address = (POINTER) ROUNDUP(virtual_break_value);

      /* Search the list upward for a heap which is large enough. */
      while ((char *) h->end < (char *) MEM_ROUNDUP((char *)address + get))
	{
	  h = h->next;
	  if (h == NIL_HEAP)
	    break;
	  address = (POINTER) ROUNDUP(h->start);
	}

      /* If not found, obatin more space. */
      if (h == NIL_HEAP)
	{
	  get += extra_bytes + page_size;

	  if (r_alloc_freeze_level > 0 || ! obtain(address, get))
	    return 0;

	  if (first_heap == last_heap)
	      address = (POINTER) ROUNDUP(virtual_break_value);
	  else
	      address = (POINTER) ROUNDUP(last_heap->start);
	  h = last_heap;
	}

      new_bloc_start = (POINTER) MEM_ROUNDUP((char *)address + get);

      if (first_heap->bloc_start < new_bloc_start)
	{
	  /* Move all blocs upward. */
	  if (r_alloc_freeze_level > 0
	      || ! relocate_blocs (first_bloc, h, new_bloc_start))
	    return 0;

	  /* Note that (POINTER)(h+1) <= new_bloc_start since
	     get >= page_size, so the following does not destroy the heap
	     header. */
	  for (b = last_bloc; b != NIL_BLOC; b = b->prev)
	    {
	      safe_bcopy (b->data, b->new_data, b->size);
	      *b->variable = b->data = b->new_data;
	    }

	  h->bloc_start = new_bloc_start;
	}

      if (h != first_heap)
	{
	  /* Give up managing heaps below the one the new
	     virtual_break_value points to. */
	  first_heap->prev = NIL_HEAP;
	  first_heap->next = h->next;
	  first_heap->start = h->start;
	  first_heap->end = h->end;
	  first_heap->bloc_start = h->bloc_start;

	  if (first_heap->next)
	    first_heap->next->prev = first_heap;
	  else
	    last_heap = first_heap;
	}

      bzero (address, size);
    }
  else /* size < 0 */
    {
      SIZE excess = (char *)first_heap->bloc_start
		      - ((char *)virtual_break_value + size);

      address = virtual_break_value;

      if (r_alloc_freeze_level == 0 && excess > 2 * extra_bytes)
	{
	  excess -= extra_bytes;
	  first_heap->bloc_start
	      = (POINTER) MEM_ROUNDUP((char *)first_heap->bloc_start - excess);

	  relocate_blocs(first_bloc, first_heap, first_heap->bloc_start);

	  for (b = first_bloc; b != NIL_BLOC; b = b->next)
	    {
	      safe_bcopy (b->data, b->new_data, b->size);
	      *b->variable = b->data = b->new_data;
	    }
	}

      if ((char *)virtual_break_value + size < (char *)first_heap->start)
	{
	  /* We found an additional space below the first heap */
	  first_heap->start = (POINTER) ((char *)virtual_break_value + size);
	}
    }

  virtual_break_value = (POINTER) ((char *)address + size);
  break_value = last_bloc ? last_bloc->data + last_bloc->size
		    : first_heap->bloc_start;
  if (size < 0)
    relinquish();

  return address;
}

/* Allocate a relocatable bloc of storage of size SIZE.  A pointer to
   the data is returned in *PTR.  PTR is thus the address of some variable
   which will use the data area.

   If we can't allocate the necessary memory, set *PTR to zero, and
   return zero.  */

POINTER
r_alloc (ptr, size)
     POINTER *ptr;
     SIZE size;
{
  register bloc_ptr new_bloc;

  if (! r_alloc_initialized)
    r_alloc_init ();

  new_bloc = get_bloc (MEM_ROUNDUP(size));
  if (new_bloc)
    {
      new_bloc->variable = ptr;
      *ptr = new_bloc->data;
    }
  else
    *ptr = 0;

  return *ptr;
}

/* Free a bloc of relocatable storage whose data is pointed to by PTR.
   Store 0 in *PTR to show there's no block allocated.  */

void
r_alloc_free (ptr)
     register POINTER *ptr;
{
  register bloc_ptr dead_bloc;

  dead_bloc = find_bloc (ptr);
  if (dead_bloc == NIL_BLOC)
    abort ();

  free_bloc (dead_bloc);
  *ptr = 0;
}

/* Given a pointer at address PTR to relocatable data, resize it to SIZE.
   Do this by shifting all blocks above this one up in memory, unless
   SIZE is less than or equal to the current bloc size, in which case
   do nothing.

   Change *PTR to reflect the new bloc, and return this value.

   If more memory cannot be allocated, then leave *PTR unchanged, and
   return zero.  */

POINTER
r_re_alloc (ptr, size)
     POINTER *ptr;
     SIZE size;
{
  register bloc_ptr bloc;

  bloc = find_bloc (ptr);
  if (bloc == NIL_BLOC)
    abort ();

  if (size <= bloc->size)
    /* Wouldn't it be useful to actually resize the bloc here?  */
    return *ptr;

  if (! resize_bloc (bloc, MEM_ROUNDUP(size)))
    return 0;

  return *ptr;
}

/* Disable relocations, after making room for at least SIZE bytes
   of non-relocatable heap if possible.  The relocatable blocs are
   guaranteed to hold still until thawed, even if this means that
   malloc must return a null pointer.  */
void
r_alloc_freeze (size)
     long size;
{
  /* If already frozen, we can't make any more room, so don't try.  */
  if (r_alloc_freeze_level > 0)
    size = 0;
  /* If we can't get the amount requested, half is better than nothing.  */
  while (size > 0 && r_alloc_sbrk (size) == 0)
    size /= 2;
  ++r_alloc_freeze_level;
  if (size > 0)
    r_alloc_sbrk (-size);
}

void
r_alloc_thaw ()
{
  if (--r_alloc_freeze_level < 0)
    abort ();
}

/* The hook `malloc' uses for the function which gets more space
   from the system.  */
extern POINTER (*__morecore) ();

/* Initialize various things for memory allocation. */

static void
r_alloc_init ()
{
  static struct heap heap_base;
  POINTER end;

  if (r_alloc_initialized)
    return;

  r_alloc_initialized = 1;
  real_morecore = __morecore;
  __morecore = r_alloc_sbrk;

  first_heap = last_heap = &heap_base;
  first_heap->next = first_heap->prev = NIL_HEAP;
  first_heap->start = first_heap->bloc_start
    = virtual_break_value = break_value = (*real_morecore) (0);
  if (break_value == NIL)
    abort ();

  page_size = PAGE;
  extra_bytes = ROUNDUP (50000);

  first_heap->end = (POINTER) ROUNDUP (first_heap->start);

  /* The extra call to real_morecore guarantees that the end of the
     address space is a multiple of page_size, even if page_size is
     not really the page size of the system running the binary in
     which page_size is stored.  This allows a binary to be built on a
     system with one page size and run on a system with a smaller page
     size. */
  (*real_morecore) (first_heap->end - first_heap->start);

  /* Clear the rest of the last page; this memory is in our address space
     even though it is after the sbrk value.  */
  /* Doubly true, with the additional call that explicitly adds the
     rest of that page to the address space.  */
  bzero (first_heap->start, first_heap->end - first_heap->start);
  virtual_break_value = break_value = first_heap->bloc_start = first_heap->end;
  use_relocatable_buffers = 1;
}
#ifdef DEBUG
#include <assert.h>

int
r_alloc_check ()
{
    int found = 0;
    heap_ptr h, ph = 0;
    bloc_ptr b, pb = 0;

    if (!r_alloc_initialized)
      return;

    assert(first_heap);
    assert(last_heap->end <= (POINTER) sbrk(0));
    assert((POINTER) first_heap < first_heap->start);
    assert(first_heap->start <= virtual_break_value);
    assert(virtual_break_value <= first_heap->end);

    for (h = first_heap; h; h = h->next)
      {
	assert(h->prev == ph);
	assert((POINTER) ROUNDUP(h->end) == h->end);
	assert((POINTER) MEM_ROUNDUP(h->start) == h->start);
	assert((POINTER) MEM_ROUNDUP(h->bloc_start) == h->bloc_start);
	assert(h->start <= h->bloc_start && h->bloc_start <= h->end);

	if (ph)
	  {
	    assert (ph->end < h->start);
	    assert (h->start <= (POINTER)h && (POINTER)(h+1) <= h->bloc_start);
	  }

	if (h->bloc_start <= break_value && break_value <= h->end)
	    found = 1;

	ph = h;
      }

    assert(found);
    assert(last_heap == ph);

    for (b = first_bloc; b; b = b->next)
      {
	assert(b->prev == pb);
	assert((POINTER) MEM_ROUNDUP(b->data) == b->data);
	assert((SIZE) MEM_ROUNDUP(b->size) == b->size);

	ph = 0;
	for (h = first_heap; h; h = h->next)
	  {
	    if (h->bloc_start <= b->data && b->data + b->size <= h->end)
		break;
	    ph = h;
	  }

	assert(h);

	if (pb && pb->data + pb->size != b->data)
	  {
	    assert(ph && b->data == h->bloc_start);
	    while (ph)
	      {
		if (ph->bloc_start <= pb->data
		    && pb->data + pb->size <= ph->end)
		  {
		    assert(pb->data + pb->size + b->size > ph->end);
		    break;
		  }
		else
		  {
		    assert(ph->bloc_start + b->size > ph->end);
		  }
		ph = ph->prev;
	      }
	  }
	pb = b;
      }

    assert(last_bloc == pb);

    if (last_bloc)
	assert(last_bloc->data + last_bloc->size == break_value);
    else
	assert(first_heap->bloc_start == break_value);
}
#endif /* DEBUG */