strcache.c

   1 /* Constant string caching for GNU Make.
   2 Copyright (C) 2006 Free Software Foundation, Inc.
   3 This file is part of GNU Make.
   4
   5 GNU Make is free software; you can redistribute it and/or modify
   6 it under the terms of the GNU General Public License as published by
   7 the Free Software Foundation; either version 2, or (at your option)
   8 any later version.
   9
  10 GNU Make is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 GNU General Public License for more details.
  14
  15 You should have received a copy of the GNU General Public License
  16 along with GNU Make; see the file COPYING.  If not, write to
  17 the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
  18 Boston, MA 02110-1301 USA.  */
  19
  20 #include "make.h"
  21
  22 #include <assert.h>
  23
  24 #include "hash.h"
  25
  26 /* The size (in bytes) of each cache buffer.  */
  27 #define CACHE_BUFFER_SIZE   (4096)
  28
  29
  30 /* A string cached here will never be freed, so we don't need to worry about
  31    reference counting.  We just store the string, and then remember it in a
  32    hash so it can be looked up again. */
  33
  34 struct strcache {
  35   struct strcache *next;    /* The next block of strings.  */
  36   char *end;                /* Pointer to the beginning of the free space.  */
  37   int count;                /* # of strings in this buffer (for stats).  */
  38   int bytesfree;            /* The amount of the buffer that is free.  */
  39   char buffer[1];           /* The buffer comes after this.  */
  40 };
  41
  42 static int bufsize = CACHE_BUFFER_SIZE;
  43 static struct strcache *strcache = NULL;
  44
  45 static struct strcache *
  46 new_cache()
  47 {
  48   struct strcache *new;
  49   new = (struct strcache *) xmalloc (sizeof (*new) + bufsize);
  50   new->end = new->buffer;
  51   new->count = 0;
  52   new->bytesfree = bufsize;
  53
  54   new->next = strcache;
  55   strcache = new;
  56
  57   return new;
  58 }
  59
  60 static const char *
  61 add_string(const char *str, int len)
  62 {
  63   struct strcache *best = NULL;
  64   struct strcache *sp;
  65   const char *res;
  66
  67   /* If the string we want is too large to fit into a single buffer, then we're
  68      screwed; nothing will ever fit!  Change the maximum size of the cache to
  69      be big enough.  */
  70   if (len > bufsize)
  71     bufsize = len * 2;
  72
  73   /* First, find a cache with enough free space.  We always look through all
  74      the blocks and choose the one with the best fit (the one that leaves the
  75      least amount of space free).  */
  76   for (sp = strcache; sp != NULL; sp = sp->next)
  77     if (sp->bytesfree > len && (!best || best->bytesfree > sp->bytesfree))
  78       best = sp;
  79
  80   /* If nothing is big enough, make a new cache.  */
  81   if (!best)
  82     best = new_cache();
  83
  84   assert (best->bytesfree > len);
  85
  86   /* Add the string to the best cache.  */
  87   res = best->end;
  88   memcpy (best->end, str, len);
  89   best->end += len;
  90   *(best->end++) = '\0';
  91   best->bytesfree -= len + 1;
  92   ++best->count;
  93
  94   return res;
  95 }
  96
  97
  98 /* Hash table of strings in the cache.  */
  99
 100 static unsigned long
 101 str_hash_1 (const void *key)
 102 {
 103   return_ISTRING_HASH_1 ((const char *) key);
 104 }
 105
 106 static unsigned long
 107 str_hash_2 (const void *key)
 108 {
 109   return_ISTRING_HASH_2 ((const char *) key);
 110 }
 111
 112 static int
 113 str_hash_cmp (const void *x, const void *y)
 114 {
 115   return_ISTRING_COMPARE ((const char *) x, (const char *) y);
 116 }
 117
 118 static struct hash_table strings;
 119
 120 static const char *
 121 add_hash (const char *str, int len)
 122 {
 123   /* Look up the string in the hash.  If it's there, return it.  */
 124   char **slot = (char **) hash_find_slot (&strings, str);
 125   const char *key = *slot;
 126
 127   if (!HASH_VACANT (key))
 128     return key;
 129
 130   /* Not there yet so add it to a buffer, then into the hash table.  */
 131   key = add_string (str, len);
 132   hash_insert_at (&strings, key, slot);
 133   return key;
 134 }
 135
 136 /* Returns true if the string is in the cache; false if not.  */
 137 int
 138 strcache_iscached (const char *str)
 139 {
 140   struct strcache *sp;
 141
 142   for (sp = strcache; sp != 0; sp = sp->next)
 143     if (str >= sp->buffer && str < sp->end)
 144       return 1;
 145
 146   return 0;
 147 }
 148
 149 /* If the string is already in the cache, return a pointer to the cached
 150    version.  If not, add it then return a pointer to the cached version.
 151    Note we do NOT take control of the string passed in.  */
 152 const char *
 153 strcache_add (const char *str)
 154 {
 155   return add_hash (str, strlen (str));
 156 }
 157
 158 const char *
 159 strcache_add_len (const char *str, int len)
 160 {
 161   char *key = alloca (len + 1);
 162   memcpy (key, str, len);
 163   key[len] = '\0';
 164
 165   return add_hash (key, len);
 166 }
 167
 168 int
 169 strcache_setbufsize(int size)
 170 {
 171   if (size > bufsize)
 172     bufsize = size;
 173   return bufsize;
 174 }
 175
 176 void
 177 strcache_init (void)
 178 {
 179   hash_init (&strings, 1000, str_hash_1, str_hash_2, str_hash_cmp);
 180 }
 181
 182
 183 /* Generate some stats output.  */
 184
 185 void
 186 strcache_print_stats (const char *prefix)
 187 {
 188   int numbuffs = 0, numstrs = 0;
 189   int totsize = 0, avgsize, maxsize = 0, minsize = bufsize;
 190   int totfree = 0, avgfree, maxfree = 0, minfree = bufsize;
 191   const struct strcache *sp;
 192
 193   for (sp = strcache; sp != NULL; sp = sp->next)
 194     {
 195       int bf = sp->bytesfree;
 196       int sz = (sp->end - sp->buffer) + bf;
 197
 198       ++numbuffs;
 199       numstrs += sp->count;
 200
 201       totsize += sz;
 202       maxsize = (sz > maxsize ? sz : maxsize);
 203       minsize = (sz < minsize ? sz : minsize);
 204
 205       totfree += bf;
 206       maxfree = (bf > maxfree ? bf : maxfree);
 207       minfree = (bf < minfree ? bf : minfree);
 208     }
 209
 210   avgsize = numbuffs ? (int)(totsize / numbuffs) : 0;
 211   avgfree = numbuffs ? (int)(totfree / numbuffs) : 0;
 212
 213   printf ("\n%s # of strings in strcache: %d\n", prefix, numstrs);
 214   printf ("%s # of strcache buffers: %d\n", prefix, numbuffs);
 215   printf ("%s strcache size: total = %d / max = %d / min = %d / avg = %d\n",
 216           prefix, totsize, maxsize, minsize, avgsize);
 217   printf ("%s strcache free: total = %d / max = %d / min = %d / avg = %d\n",
 218           prefix, totfree, maxfree, minfree, avgfree);
 219 }