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 /*doc*
  22 @section File Caching
  23 The file caching mechanism is embedded within BFD and allows the application to open as many
  24 BFDs as it wants without regard to the underlying operating system's
  25 file descriptor limit (often as low as 20 open files).
  26
  27 The module in @code{cache.c} maintains a least recently used list of
  28 @code{BFD_CACHE_MAX_OPEN} files, and exports the name
  29 @code{bfd_cache_lookup} which runs around and makes sure that the
  30 required BFD is open. If not, then it chooses a file to close, closes
  31 it and opens the one wanted, returning its file handle.
  32
  33 */
  34
  35
  36
  37 /* $Id$ */
  38 #include <sysdep.h>
  39 #include "bfd.h"
  40 #include "libbfd.h"
  41
  42
  43 /*proto-internal* BFD_CACHE_MAX_OPEN
  44 The maxiumum number of files which the cache will keep open at one
  45 time.
  46 *+
  47 #define BFD_CACHE_MAX_OPEN 10
  48 *-
  49
  50 */
  51
  52
  53 static int open_files;
  54
  55 static bfd *cache_sentinel;     /* Chain of BFDs with active fds we've
  56                                    opened */
  57
  58 /*proto-internal*  bfd_last_cache
  59 Zero, or a pointer to the topmost BFD on the chain.  This is used by
  60 the @code{bfd_cache_lookup} macro in @file{libbfd.h} to determine when
  61 it can avoid a function call.
  62 *+
  63 extern bfd *bfd_last_cache;
  64 *-
  65
  66 */
  67
  68 bfd *bfd_last_cache;
  69
  70 /*proto-internal*  bfd_cache_lookup
  71 Checks to see if the required BFD is the same as the last one looked
  72 up. If so then it can use the iostream in the BFD with impunity, since
  73 it can't have changed since the last lookup, otherwise it has to
  74 perform the complicated lookup function
  75 *+
  76 #define bfd_cache_lookup(x) \
  77      ((x)==bfd_last_cache? \
  78         (FILE*)(bfd_last_cache->iostream): \
  79          bfd_cache_lookup_worker(x))
  80
  81 *-
  82
  83 */
  84
  85 static void bfd_cache_delete();
  86
  87
  88 static void
  89 DEFUN_VOID(close_one)
  90 {
  91     bfd *kill = cache_sentinel;
  92     if (kill == 0)              /* Nothing in the cache */
  93         return ;
  94
  95     /* We can only close files that want to play this game.  */
  96     while (!kill->cacheable) {
  97         kill = kill->lru_prev;
  98         if (kill == cache_sentinel) /* Nobody wants to play */
  99            return ;
 100     }
 101
 102     kill->where = ftell((FILE *)(kill->iostream));
 103     bfd_cache_delete(kill);
 104 }
 105
 106 /* Cuts the BFD abfd out of the chain in the cache */
 107 static void
 108 DEFUN(snip,(abfd),
 109       bfd *abfd)
 110 {
 111   abfd->lru_prev->lru_next = abfd->lru_next;
 112   abfd->lru_next->lru_prev = abfd->lru_prev;
 113   if (cache_sentinel == abfd) cache_sentinel = (bfd *)NULL;
 114 }
 115
 116 static void
 117 DEFUN(bfd_cache_delete,(abfd),
 118       bfd *abfd)
 119 {
 120   fclose ((FILE *)(abfd->iostream));
 121   snip (abfd);
 122   abfd->iostream = NULL;
 123   open_files--;
 124   bfd_last_cache = 0;
 125 }
 126
 127 static bfd *
 128 DEFUN(insert,(x,y),
 129       bfd *x AND
 130       bfd *y)
 131 {
 132   if (y) {
 133     x->lru_next = y;
 134     x->lru_prev = y->lru_prev;
 135     y->lru_prev->lru_next = x;
 136     y->lru_prev = x;
 137
 138   }
 139   else {
 140     x->lru_prev = x;
 141     x->lru_next = x;
 142   }
 143   return x;
 144 }
 145 \f
 146
 147 /*proto-internal*
 148 *i bfd_cache_init
 149 Initialize a BFD by putting it on the cache LRU.
 150 *; PROTO(void, bfd_cache_init, (bfd *));
 151 *-*/
 152
 153 void
 154 DEFUN(bfd_cache_init,(abfd),
 155       bfd *abfd)
 156 {
 157   cache_sentinel = insert(abfd, cache_sentinel);
 158 }
 159
 160
 161 /*proto-internal*
 162 *i bfd_cache_close
 163 Remove the BFD from the cache. If the attatched file is open, then close it too.
 164 *; PROTO(void, bfd_cache_close, (bfd *));
 165 *-*/
 166 void
 167 DEFUN(bfd_cache_close,(abfd),
 168       bfd *abfd)
 169 {
 170   /* If this file is open then remove from the chain */
 171   if (abfd->iostream)
 172     {
 173       bfd_cache_delete(abfd);
 174     }
 175 }
 176
 177 /*proto-internal*
 178 *i bfd_open_file
 179 Call the OS to open a file for this BFD.  Returns the FILE *
 180 (possibly null) that results from this operation.  Sets up the
 181 BFD so that future accesses know the file is open. If the FILE *
 182 returned is null, then there is won't have been put in the cache, so
 183 it won't have to be removed from it.
 184 *; PROTO(FILE *, bfd_open_file, (bfd *));
 185 *-*/
 186 FILE *
 187 DEFUN(bfd_open_file, (abfd),
 188       bfd *abfd)
 189 {
 190   abfd->cacheable = true;       /* Allow it to be closed later. */
 191   if(open_files >= BFD_CACHE_MAX_OPEN) {
 192     close_one();
 193   }
 194   switch (abfd->direction) {
 195   case read_direction:
 196   case no_direction:
 197     abfd->iostream = (char *) fopen(abfd->filename, "r");
 198     break;
 199   case both_direction:
 200   case write_direction:
 201     if (abfd->opened_once == true) {
 202       abfd->iostream = (char *) fopen(abfd->filename, "r+");
 203       if (!abfd->iostream) {
 204         abfd->iostream = (char *) fopen(abfd->filename, "w+");
 205       }
 206     } else {
 207       /*open for creat */
 208       abfd->iostream = (char *) fopen(abfd->filename, "w");
 209       abfd->opened_once = true;
 210     }
 211     break;
 212   }
 213   if (abfd->iostream) {
 214     open_files++;
 215     bfd_cache_init (abfd);
 216   }
 217
 218   return (FILE *)(abfd->iostream);
 219 }
 220
 221 /*proto-internal*
 222 *i bfd_cache_lookup_worker
 223 Called when the macro @code{bfd_cache_lookup} fails to find a quick
 224 answer. Finds a file descriptor for this BFD.  If necessary, it open it.
 225 If there are already more than BFD_CACHE_MAX_OPEN files open, it trys to close
 226 one first, to avoid running out of file descriptors.
 227 *; PROTO(FILE *, bfd_cache_lookup_worker, (bfd *));
 228
 229 *-*/
 230
 231 FILE *
 232 DEFUN(bfd_cache_lookup_worker,(abfd),
 233       bfd *abfd)
 234 {
 235   if (abfd->my_archive)
 236       {
 237         abfd = abfd->my_archive;
 238       }
 239   /* Is this file already open .. if so then quick exit */
 240   if (abfd->iostream)
 241       {
 242         if (abfd != cache_sentinel) {
 243           /* Place onto head of lru chain */
 244           snip (abfd);
 245           cache_sentinel = insert(abfd, cache_sentinel);
 246         }
 247       }
 248   /* This is a BFD without a stream -
 249      so it must have been closed or never opened.
 250      find an empty cache entry and use it.  */
 251   else
 252       {
 253
 254         if (open_files >= BFD_CACHE_MAX_OPEN)
 255             {
 256               close_one();
 257             }
 258
 259         BFD_ASSERT(bfd_open_file (abfd) != (FILE *)NULL) ;
 260         fseek((FILE *)(abfd->iostream), abfd->where, false);
 261       }
 262   bfd_last_cache = abfd;
 263   return (FILE *)(abfd->iostream);
 264 }