make/strcache.c

/* Constant string caching for GNU Make.
Copyright (C) 2006 Free Software Foundation, Inc.
This file is part of GNU Make.

GNU Make 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 2, or (at your option) any later version.

GNU Make 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 Make; see the file COPYING.  If not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.  */

#include "make.h"

#include <assert.h>

#include "hash.h"

/* The size (in bytes) of each cache buffer.  */
#define CACHE_BUFFER_SIZE   (4096)


/* A string cached here will never be freed, so we don't need to worry about
   reference counting.  We just store the string, and then remember it in a
   hash so it can be looked up again. */

struct strcache {
  struct strcache *next;    /* The next block of strings.  */
  char *end;                /* Pointer to the beginning of the free space.  */
  int count;                /* # of strings in this buffer (for stats).  */
  int bytesfree;            /* The amount of the buffer that is free.  */
  char buffer[1];           /* The buffer comes after this.  */
};

static int bufsize = CACHE_BUFFER_SIZE;
static struct strcache *strcache = NULL;

static struct strcache *
new_cache()
{
  struct strcache *new;
  new = (struct strcache *) xmalloc (sizeof (*new) + bufsize);
  new->end = new->buffer;
  new->count = 0;
  new->bytesfree = bufsize;

  new->next = strcache;
  strcache = new;

  return new;
}

static const char *
add_string(const char *str, int len)
{
  struct strcache *best = NULL;
  struct strcache *sp;
  const char *res;

  /* If the string we want is too large to fit into a single buffer, then we're
     screwed; nothing will ever fit!  Change the maximum size of the cache to
     be big enough.  */
  if (len > bufsize)
    bufsize = len * 2;

  /* First, find a cache with enough free space.  We always look through all
     the blocks and choose the one with the best fit (the one that leaves the
     least amount of space free).  */
  for (sp = strcache; sp != NULL; sp = sp->next)
    if (sp->bytesfree > len && (!best || best->bytesfree > sp->bytesfree))
      best = sp;

  /* If nothing is big enough, make a new cache.  */
  if (!best)
    best = new_cache();

  assert (best->bytesfree > len);

  /* Add the string to the best cache.  */
  res = best->end;
  memcpy (best->end, str, len);
  best->end += len;
  *(best->end++) = '\0';
  best->bytesfree -= len + 1;
  ++best->count;

  return res;
}


/* Hash table of strings in the cache.  */

static unsigned long
str_hash_1 (const void *key)
{
  return_ISTRING_HASH_1 ((const char *) key);
}

static unsigned long
str_hash_2 (const void *key)
{
  return_ISTRING_HASH_2 ((const char *) key);
}

static int
str_hash_cmp (const void *x, const void *y)
{
  return_ISTRING_COMPARE ((const char *) x, (const char *) y);
}

static struct hash_table strings;

static const char *
add_hash (const char *str, int len)
{
  /* Look up the string in the hash.  If it's there, return it.  */
  char **slot = (char **) hash_find_slot (&strings, str);
  const char *key = *slot;

  if (!HASH_VACANT (key))
    return key;

  /* Not there yet so add it to a buffer, then into the hash table.  */
  key = add_string (str, len);
  hash_insert_at (&strings, key, slot);
  return key;
}

/* Returns true if the string is in the cache; false if not.  */
int
strcache_iscached (const char *str)
{
  struct strcache *sp;

  for (sp = strcache; sp != 0; sp = sp->next)
    if (str >= sp->buffer && str < sp->end)
      return 1;

  return 0;
}

/* If the string is already in the cache, return a pointer to the cached
   version.  If not, add it then return a pointer to the cached version.
   Note we do NOT take control of the string passed in.  */
const char *
strcache_add (const char *str)
{
  return add_hash (str, strlen (str));
}

const char *
strcache_add_len (const char *str, int len)
{
  char *key = alloca (len + 1);
  memcpy (key, str, len);
  key[len] = '\0';

  return add_hash (key, len);
}

int
strcache_setbufsize(int size)
{
  if (size > bufsize)
    bufsize = size;
  return bufsize;
}

void
strcache_init (void)
{
  hash_init (&strings, 1000, str_hash_1, str_hash_2, str_hash_cmp);
}


/* Generate some stats output.  */

void
strcache_print_stats (const char *prefix)
{
  int numbuffs = 0, numstrs = 0;
  int totsize = 0, avgsize, maxsize = 0, minsize = bufsize;
  int totfree = 0, avgfree, maxfree = 0, minfree = bufsize;
  const struct strcache *sp;

  for (sp = strcache; sp != NULL; sp = sp->next)
    {
      int bf = sp->bytesfree;
      int sz = (sp->end - sp->buffer) + bf;

      ++numbuffs;
      numstrs += sp->count;

      totsize += sz;
      maxsize = (sz > maxsize ? sz : maxsize);
      minsize = (sz < minsize ? sz : minsize);

      totfree += bf;
      maxfree = (bf > maxfree ? bf : maxfree);
      minfree = (bf < minfree ? bf : minfree);
    }

  avgsize = numbuffs ? (int)(totsize / numbuffs) : 0;
  avgfree = numbuffs ? (int)(totfree / numbuffs) : 0;

  printf (_("\n%s # of strings in strcache: %d\n"), prefix, numstrs);
  printf (_("%s # of strcache buffers: %d\n"), prefix, numbuffs);
  printf (_("%s strcache size: total = %d / max = %d / min = %d / avg = %d\n"),
          prefix, totsize, maxsize, minsize, avgsize);
  printf (_("%s strcache free: total = %d / max = %d / min = %d / avg = %d\n"),
          prefix, totfree, maxfree, minfree, avgfree);
}