bfd/cache.c

   1 /* BFD library -- caching of file descriptors.
   2    Copyright (C) 1990-1991 Free Software Foundation, Inc.
   3    Hacked by Steve Chamberlain of Cygnus Support (steve@cygnus.com).
   4
   5 This file is part of BFD, the Binary File Descriptor library.
   6
   7 This program is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2 of the License, or
  10 (at your option) any later version.
  11
  12 This program is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with this program; if not, write to the Free Software
  19 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  20
  21 /*
  22 SECTION
  23         File Caching
  24
  25         The file caching mechanism is embedded within BFD and allows
  26         the application to open as many BFDs as it wants without
  27         regard to the underlying operating system's file descriptor
  28         limit (often as low as 20 open files).  The module in
  29         <<cache.c>> maintains a least recently used list of
  30         <<BFD_CACHE_MAX_OPEN>> files, and exports the name
  31         <<bfd_cache_lookup>> which runs around and makes sure that
  32         the required BFD is open. If not, then it chooses a file to
  33         close, closes it and opens the one wanted, returning its file
  34         handle.
  35
  36 */
  37
  38 /* $Id$ */
  39
  40 #include "bfd.h"
  41 #include "sysdep.h"
  42 #include "libbfd.h"
  43
  44 /*
  45 INTERNAL_FUNCTION
  46         BFD_CACHE_MAX_OPEN macro
  47
  48 DESCRIPTION
  49         The maxiumum number of files which the cache will keep open at
  50         one time.
  51
  52 .#define BFD_CACHE_MAX_OPEN 10
  53
  54 */
  55
  56
  57 static int open_files;
  58
  59 static bfd *cache_sentinel;     /* Chain of BFDs with active fds we've
  60                                    opened */
  61
  62 /*
  63 INTERNAL_FUNCTION
  64         bfd_last_cache
  65
  66 SYNOPSIS
  67         extern bfd *bfd_last_cache;
  68
  69 DESCRIPTION
  70         Zero, or a pointer to the topmost BFD on the chain.  This is
  71         used by the <<bfd_cache_lookup>> macro in @file{libbfd.h} to
  72         determine when it can avoid a function call.
  73 */
  74
  75 bfd *bfd_last_cache;
  76
  77 /*
  78  * INTERNAL_FUNCTION
  79  *      bfd_cache_lookup
  80  *
  81  * DESCRIPTION
  82  *      Checks to see if the required BFD is the same as the last one
  83  *      looked up. If so then it can use the iostream in the BFD with
  84  *      impunity, since it can't have changed since the last lookup,
  85  *      otherwise it has to perform the complicated lookup function
  86  *
  87  * .#define bfd_cache_lookup(x) \
  88  * .    ((x)==bfd_last_cache? \
  89  * .      (FILE*)(bfd_last_cache->iostream): \
  90  * .       bfd_cache_lookup_worker(x))
  91  *
  92  *
  93  */
  94
  95 static void bfd_cache_delete();
  96
  97
  98 static void
  99 DEFUN_VOID(close_one)
 100 {
 101     bfd *kill = cache_sentinel;
 102     if (kill == 0)              /* Nothing in the cache */
 103         return ;
 104
 105     /* We can only close files that want to play this game.  */
 106     while (!kill->cacheable) {
 107         kill = kill->lru_prev;
 108         if (kill == cache_sentinel) /* Nobody wants to play */
 109            return ;
 110     }
 111
 112     kill->where = ftell((FILE *)(kill->iostream));
 113     bfd_cache_delete(kill);
 114 }
 115
 116 /* Cuts the BFD abfd out of the chain in the cache */
 117 static void
 118 DEFUN(snip,(abfd),
 119       bfd *abfd)
 120 {
 121   abfd->lru_prev->lru_next = abfd->lru_next;
 122   abfd->lru_next->lru_prev = abfd->lru_prev;
 123   if (cache_sentinel == abfd) cache_sentinel = (bfd *)NULL;
 124 }
 125
 126 static void
 127 DEFUN(bfd_cache_delete,(abfd),
 128       bfd *abfd)
 129 {
 130   fclose ((FILE *)(abfd->iostream));
 131   snip (abfd);
 132   abfd->iostream = NULL;
 133   open_files--;
 134   bfd_last_cache = 0;
 135 }
 136
 137 static bfd *
 138 DEFUN(insert,(x,y),
 139       bfd *x AND
 140       bfd *y)
 141 {
 142   if (y) {
 143     x->lru_next = y;
 144     x->lru_prev = y->lru_prev;
 145     y->lru_prev->lru_next = x;
 146     y->lru_prev = x;
 147
 148   }
 149   else {
 150     x->lru_prev = x;
 151     x->lru_next = x;
 152   }
 153   return x;
 154 }
 155 \f
 156
 157 /*
 158 INTERNAL_FUNCTION
 159         bfd_cache_init
 160
 161 SYNOPSIS
 162         void  bfd_cache_init (bfd *);
 163
 164 DESCRIPTION
 165         Initialize a BFD by putting it on the cache LRU.
 166 */
 167
 168 void
 169 DEFUN(bfd_cache_init,(abfd),
 170       bfd *abfd)
 171 {
 172   cache_sentinel = insert(abfd, cache_sentinel);
 173 }
 174
 175
 176 /*
 177 INTERNAL_FUNCTION
 178         bfd_cache_close
 179
 180 DESCRIPTION
 181         Remove the BFD from the cache. If the attached file is open,
 182         then close it too.
 183
 184 SYNOPSIS
 185         void bfd_cache_close (bfd *);
 186 */
 187 void
 188 DEFUN(bfd_cache_close,(abfd),
 189       bfd *abfd)
 190 {
 191   /* If this file is open then remove from the chain */
 192   if (abfd->iostream)
 193     {
 194       bfd_cache_delete(abfd);
 195     }
 196 }
 197
 198 /*
 199 INTERNAL_FUNCTION
 200         bfd_open_file
 201
 202 DESCRIPTION
 203         Call the OS to open a file for this BFD.  Returns the FILE *
 204         (possibly null) that results from this operation.  Sets up the
 205         BFD so that future accesses know the file is open. If the FILE
 206         * returned is null, then there is won't have been put in the
 207         cache, so it won't have to be removed from it.
 208
 209 SYNOPSIS
 210         FILE* bfd_open_file(bfd *);
 211 */
 212
 213 FILE *
 214 DEFUN(bfd_open_file, (abfd),
 215       bfd *abfd)
 216 {
 217   abfd->cacheable = true;       /* Allow it to be closed later. */
 218   if(open_files >= BFD_CACHE_MAX_OPEN) {
 219     close_one();
 220   }
 221   switch (abfd->direction) {
 222   case read_direction:
 223   case no_direction:
 224     abfd->iostream = (char *) fopen(abfd->filename, "rb");
 225     break;
 226   case both_direction:
 227   case write_direction:
 228     if (abfd->opened_once == true) {
 229       abfd->iostream = (char *) fopen(abfd->filename, "r+b");
 230       if (!abfd->iostream) {
 231         abfd->iostream = (char *) fopen(abfd->filename, "w+b");
 232       }
 233     } else {
 234       /*open for creat */
 235       abfd->iostream = (char *) fopen(abfd->filename, "wb");
 236       abfd->opened_once = true;
 237     }
 238     break;
 239   }
 240   if (abfd->iostream) {
 241     open_files++;
 242     bfd_cache_init (abfd);
 243   }
 244
 245   return (FILE *)(abfd->iostream);
 246 }
 247
 248 /*
 249 INTERNAL_FUNCTION
 250         bfd_cache_lookup_worker
 251
 252 DESCRIPTION
 253         Called when the macro <<bfd_cache_lookup>> fails to find a
 254         quick answer. Finds a file descriptor for this BFD.  If
 255         necessary, it open it. If there are already more than
 256         BFD_CACHE_MAX_OPEN files open, it trys to close one first, to
 257         avoid running out of file descriptors.
 258
 259 SYNOPSIS
 260         FILE *bfd_cache_lookup_worker(bfd *);
 261
 262 */
 263
 264 FILE *
 265 DEFUN(bfd_cache_lookup_worker,(abfd),
 266       bfd *abfd)
 267 {
 268   if (abfd->my_archive)
 269       {
 270         abfd = abfd->my_archive;
 271       }
 272   /* Is this file already open .. if so then quick exit */
 273   if (abfd->iostream)
 274       {
 275         if (abfd != cache_sentinel) {
 276           /* Place onto head of lru chain */
 277           snip (abfd);
 278           cache_sentinel = insert(abfd, cache_sentinel);
 279         }
 280       }
 281   /* This is a BFD without a stream -
 282      so it must have been closed or never opened.
 283      find an empty cache entry and use it.  */
 284   else
 285       {
 286
 287         if (open_files >= BFD_CACHE_MAX_OPEN)
 288             {
 289               close_one();
 290             }
 291
 292         BFD_ASSERT(bfd_open_file (abfd) != (FILE *)NULL) ;
 293         fseek((FILE *)(abfd->iostream), abfd->where, false);
 294       }
 295   bfd_last_cache = abfd;
 296   return (FILE *)(abfd->iostream);
 297 }