unwind_prot.c

   1 /* unwind_prot.c - a simple unwind-protect system for internal variables */
   2
   3 /* I can't stand it anymore!  Please can't we just write the
   4    whole Unix system in lisp or something? */
   5
   6 /* Copyright (C) 1987-2009 Free Software Foundation, Inc.
   7
   8    This file is part of GNU Bash, the Bourne Again SHell.
   9
  10    Bash is free software: you can redistribute it and/or modify
  11    it under the terms of the GNU General Public License as published by
  12    the Free Software Foundation, either version 3 of the License, or
  13    (at your option) any later version.
  14
  15    Bash is distributed in the hope that it will be useful,
  16    but WITHOUT ANY WARRANTY; without even the implied warranty of
  17    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18    GNU General Public License for more details.
  19
  20    You should have received a copy of the GNU General Public License
  21    along with Bash.  If not, see <http://www.gnu.org/licenses/>.
  22 */
  23
  24 /* **************************************************************** */
  25 /*                                                                  */
  26 /*                    Unwind Protection Scheme for Bash             */
  27 /*                                                                  */
  28 /* **************************************************************** */
  29 #include "config.h"
  30
  31 #include "bashtypes.h"
  32 #include "bashansi.h"
  33
  34 #if defined (HAVE_UNISTD_H)
  35 #  include <unistd.h>
  36 #endif
  37
  38 #if STDC_HEADERS
  39 #  include <stddef.h>
  40 #endif
  41
  42 #ifndef offsetof
  43 #  define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
  44 #endif
  45
  46 #include "command.h"
  47 #include "general.h"
  48 #include "unwind_prot.h"
  49 #include "quit.h"
  50 #include "sig.h"
  51 #include "error.h"      /* for internal_warning */
  52
  53 /* Structure describing a saved variable and the value to restore it to.  */
  54 typedef struct {
  55   char *variable;
  56   int size;
  57   char desired_setting[1]; /* actual size is `size' */
  58 } SAVED_VAR;
  59
  60 /* If HEAD.CLEANUP is null, then ARG.V contains a tag to throw back to.
  61    If HEAD.CLEANUP is restore_variable, then SV.V contains the saved
  62    variable.  Otherwise, call HEAD.CLEANUP (ARG.V) to clean up.  */
  63 typedef union uwp {
  64   struct uwp_head {
  65     union uwp *next;
  66     Function *cleanup;
  67   } head;
  68   struct {
  69     struct uwp_head uwp_head;
  70     char *v;
  71   } arg;
  72   struct {
  73     struct uwp_head uwp_head;
  74     SAVED_VAR v;
  75   } sv;
  76 } UNWIND_ELT;
  77
  78
  79 static void without_interrupts __P((VFunction *, char *, char *));
  80 static void unwind_frame_discard_internal __P((char *, char *));
  81 static void unwind_frame_run_internal __P((char *, char *));
  82 static void add_unwind_protect_internal __P((Function *, char *));
  83 static void remove_unwind_protect_internal __P((char *, char *));
  84 static void run_unwind_protects_internal __P((char *, char *));
  85 static void clear_unwind_protects_internal __P((char *, char *));
  86 static inline void restore_variable __P((SAVED_VAR *));
  87 static void unwind_protect_mem_internal __P((char *, char *));
  88
  89 static UNWIND_ELT *unwind_protect_list = (UNWIND_ELT *)NULL;
  90
  91 #define uwpalloc(elt)   (elt) = (UNWIND_ELT *)xmalloc (sizeof (UNWIND_ELT))
  92 #define uwpfree(elt)    free(elt)
  93
  94 /* Run a function without interrupts.  This relies on the fact that the
  95    FUNCTION cannot change the value of interrupt_immediately.  (I.e., does
  96    not call QUIT (). */
  97 static void
  98 without_interrupts (function, arg1, arg2)
  99      VFunction *function;
 100      char *arg1, *arg2;
 101 {
 102   int old_interrupt_immediately;
 103
 104   old_interrupt_immediately = interrupt_immediately;
 105   interrupt_immediately = 0;
 106
 107   (*function)(arg1, arg2);
 108
 109   interrupt_immediately = old_interrupt_immediately;
 110 }
 111
 112 /* Start the beginning of a region. */
 113 void
 114 begin_unwind_frame (tag)
 115      char *tag;
 116 {
 117   add_unwind_protect ((Function *)NULL, tag);
 118 }
 119
 120 /* Discard the unwind protects back to TAG. */
 121 void
 122 discard_unwind_frame (tag)
 123      char *tag;
 124 {
 125   if (unwind_protect_list)
 126     without_interrupts (unwind_frame_discard_internal, tag, (char *)NULL);
 127 }
 128
 129 /* Run the unwind protects back to TAG. */
 130 void
 131 run_unwind_frame (tag)
 132      char *tag;
 133 {
 134   if (unwind_protect_list)
 135     without_interrupts (unwind_frame_run_internal, tag, (char *)NULL);
 136 }
 137
 138 /* Add the function CLEANUP with ARG to the list of unwindable things. */
 139 void
 140 add_unwind_protect (cleanup, arg)
 141      Function *cleanup;
 142      char *arg;
 143 {
 144   without_interrupts (add_unwind_protect_internal, (char *)cleanup, arg);
 145 }
 146
 147 /* Remove the top unwind protect from the list. */
 148 void
 149 remove_unwind_protect ()
 150 {
 151   if (unwind_protect_list)
 152     without_interrupts
 153       (remove_unwind_protect_internal, (char *)NULL, (char *)NULL);
 154 }
 155
 156 /* Run the list of cleanup functions in unwind_protect_list. */
 157 void
 158 run_unwind_protects ()
 159 {
 160   if (unwind_protect_list)
 161     without_interrupts
 162       (run_unwind_protects_internal, (char *)NULL, (char *)NULL);
 163 }
 164
 165 /* Erase the unwind-protect list.  If flags is 1, free the elements. */
 166 void
 167 clear_unwind_protect_list (flags)
 168      int flags;
 169 {
 170   char *flag;
 171
 172   if (unwind_protect_list)
 173     {
 174       flag = flags ? "" : (char *)NULL;
 175       without_interrupts
 176         (clear_unwind_protects_internal, flag, (char *)NULL);
 177     }
 178 }
 179
 180 int
 181 have_unwind_protects ()
 182 {
 183   return (unwind_protect_list != 0);
 184 }
 185
 186 /* **************************************************************** */
 187 /*                                                                  */
 188 /*                      The Actual Functions                        */
 189 /*                                                                  */
 190 /* **************************************************************** */
 191
 192 static void
 193 add_unwind_protect_internal (cleanup, arg)
 194      Function *cleanup;
 195      char *arg;
 196 {
 197   UNWIND_ELT *elt;
 198
 199   uwpalloc (elt);
 200   elt->head.next = unwind_protect_list;
 201   elt->head.cleanup = cleanup;
 202   elt->arg.v = arg;
 203   unwind_protect_list = elt;
 204 }
 205
 206 static void
 207 remove_unwind_protect_internal (ignore1, ignore2)
 208      char *ignore1, *ignore2;
 209 {
 210   UNWIND_ELT *elt;
 211
 212   elt = unwind_protect_list;
 213   if (elt)
 214     {
 215       unwind_protect_list = unwind_protect_list->head.next;
 216       uwpfree (elt);
 217     }
 218 }
 219
 220 static void
 221 run_unwind_protects_internal (ignore1, ignore2)
 222      char *ignore1, *ignore2;
 223 {
 224   unwind_frame_run_internal ((char *) NULL, (char *) NULL);
 225 }
 226
 227 static void
 228 clear_unwind_protects_internal (flag, ignore)
 229      char *flag, *ignore;
 230 {
 231   if (flag)
 232     {
 233       while (unwind_protect_list)
 234         remove_unwind_protect_internal ((char *)NULL, (char *)NULL);
 235     }
 236   unwind_protect_list = (UNWIND_ELT *)NULL;
 237 }
 238
 239 static void
 240 unwind_frame_discard_internal (tag, ignore)
 241      char *tag, *ignore;
 242 {
 243   UNWIND_ELT *elt;
 244   int found;
 245
 246   found = 0;
 247   while (elt = unwind_protect_list)
 248     {
 249       unwind_protect_list = unwind_protect_list->head.next;
 250       if (elt->head.cleanup == 0 && (STREQ (elt->arg.v, tag)))
 251         {
 252           uwpfree (elt);
 253           found = 1;
 254           break;
 255         }
 256       else
 257         uwpfree (elt);
 258     }
 259
 260   if (found == 0)
 261     internal_warning ("unwind_frame_discard: %s: frame not found", tag);
 262 }
 263
 264 /* Restore the value of a variable, based on the contents of SV.
 265    sv->desired_setting is a block of memory SIZE bytes long holding the
 266    value itself.  This block of memory is copied back into the variable. */
 267 static inline void
 268 restore_variable (sv)
 269      SAVED_VAR *sv;
 270 {
 271   FASTCOPY (sv->desired_setting, sv->variable, sv->size);
 272 }
 273
 274 static void
 275 unwind_frame_run_internal (tag, ignore)
 276      char *tag, *ignore;
 277 {
 278   UNWIND_ELT *elt;
 279   int found;
 280
 281   found = 0;
 282   while (elt = unwind_protect_list)
 283     {
 284       unwind_protect_list = elt->head.next;
 285
 286       /* If tag, then compare. */
 287       if (elt->head.cleanup == 0)
 288         {
 289           if (tag && STREQ (elt->arg.v, tag))
 290             {
 291               uwpfree (elt);
 292               found = 1;
 293               break;
 294             }
 295         }
 296       else
 297         {
 298           if (elt->head.cleanup == (Function *) restore_variable)
 299             restore_variable (&elt->sv.v);
 300           else
 301             (*(elt->head.cleanup)) (elt->arg.v);
 302         }
 303
 304       uwpfree (elt);
 305     }
 306   if (tag && found == 0)
 307     internal_warning ("unwind_frame_run: %s: frame not found", tag);
 308 }
 309
 310 static void
 311 unwind_protect_mem_internal (var, psize)
 312      char *var;
 313      char *psize;
 314 {
 315   int size, allocated;
 316   UNWIND_ELT *elt;
 317
 318   size = *(int *) psize;
 319   allocated = size + offsetof (UNWIND_ELT, sv.v.desired_setting[0]);
 320   elt = (UNWIND_ELT *)xmalloc (allocated);
 321   elt->head.next = unwind_protect_list;
 322   elt->head.cleanup = (Function *) restore_variable;
 323   elt->sv.v.variable = var;
 324   elt->sv.v.size = size;
 325   FASTCOPY (var, elt->sv.v.desired_setting, size);
 326   unwind_protect_list = elt;
 327 }
 328
 329 /* Save the value of a variable so it will be restored when unwind-protects
 330    are run.  VAR is a pointer to the variable.  SIZE is the size in
 331    bytes of VAR.  */
 332 void
 333 unwind_protect_mem (var, size)
 334      char *var;
 335      int size;
 336 {
 337   without_interrupts (unwind_protect_mem_internal, var, (char *) &size);
 338 }
 339
 340 #if defined (DEBUG)
 341 #include <stdio.h>
 342
 343 void
 344 print_unwind_protect_tags ()
 345 {
 346   UNWIND_ELT *elt;
 347
 348   elt = unwind_protect_list;
 349   while (elt)
 350     {
 351       unwind_protect_list = unwind_protect_list->head.next;
 352       if (elt->head.cleanup == 0)
 353         fprintf(stderr, "tag: %s\n", elt->arg.v);
 354       elt = unwind_protect_list;
 355     }
 356 }
 357 #endif