libguile/root.c

   1 /*      Copyright (C) 1995,1996,1997,1998, 1999, 2000 Free Software Foundation, Inc.
   2  *
   3  * This program is free software; you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation; either version 2, or (at your option)
   6  * any later version.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License
  14  * along with this software; see the file COPYING.  If not, write to
  15  * the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  16  * Boston, MA 02111-1307 USA
  17  *
  18  * As a special exception, the Free Software Foundation gives permission
  19  * for additional uses of the text contained in its release of GUILE.
  20  *
  21  * The exception is that, if you link the GUILE library with other files
  22  * to produce an executable, this does not by itself cause the
  23  * resulting executable to be covered by the GNU General Public License.
  24  * Your use of that executable is in no way restricted on account of
  25  * linking the GUILE library code into it.
  26  *
  27  * This exception does not however invalidate any other reasons why
  28  * the executable file might be covered by the GNU General Public License.
  29  *
  30  * This exception applies only to the code released by the
  31  * Free Software Foundation under the name GUILE.  If you copy
  32  * code from other Free Software Foundation releases into a copy of
  33  * GUILE, as the General Public License permits, the exception does
  34  * not apply to the code that you add in this way.  To avoid misleading
  35  * anyone as to the status of such modified files, you must delete
  36  * this exception notice from them.
  37  *
  38  * If you write modifications of your own for GUILE, it is your choice
  39  * whether to permit this exception to apply to your modifications.
  40  * If you do not wish that, delete this exception notice.  */
  41
  42 /* Software engineering face-lift by Greg J. Badros, 11-Dec-1999,
  43    gjb@cs.washington.edu, http://www.cs.washington.edu/homes/gjb */
  44
  45 \f
  46
  47 #include <stdio.h>
  48 #include "libguile/_scm.h"
  49 #include "libguile/stackchk.h"
  50 #include "libguile/dynwind.h"
  51 #include "libguile/eval.h"
  52 #include "libguile/smob.h"
  53 #include "libguile/pairs.h"
  54 #include "libguile/throw.h"
  55 #include "libguile/fluids.h"
  56 #include "libguile/ports.h"
  57
  58 #include "libguile/root.h"
  59 \f
  60
  61 SCM scm_sys_protects[SCM_NUM_PROTECTS];
  62
  63 long scm_tc16_root;
  64
  65 #ifndef USE_THREADS
  66 struct scm_root_state *scm_root;
  67 #endif
  68
  69 \f
  70
  71 static SCM
  72 mark_root (SCM root)
  73 {
  74   scm_root_state *s = SCM_ROOT_STATE (root);
  75
  76   scm_gc_mark (s->rootcont);
  77   scm_gc_mark (s->dynwinds);
  78   scm_gc_mark (s->continuation_stack);
  79   scm_gc_mark (s->continuation_stack_ptr);
  80   scm_gc_mark (s->progargs);
  81   scm_gc_mark (s->exitval);
  82   scm_gc_mark (s->cur_inp);
  83   scm_gc_mark (s->cur_outp);
  84   scm_gc_mark (s->cur_errp);
  85   scm_gc_mark (s->def_inp);
  86   scm_gc_mark (s->def_outp);
  87   scm_gc_mark (s->def_errp);
  88   /* No need to gc mark def_loadp */
  89   scm_gc_mark (s->fluids);
  90   return SCM_ROOT_STATE (root) -> parent;
  91 }
  92
  93
  94 static int
  95 print_root (SCM exp,SCM port,scm_print_state *pstate)
  96 {
  97   scm_puts ("#<root ", port);
  98   scm_intprint(SCM_SEQ (SCM_ROOT_STATE (exp) -> rootcont), 16, port);
  99   scm_putc('>', port);
 100   return 1;
 101 }
 102
 103
 104 \f
 105
 106 SCM
 107 scm_make_root (SCM parent)
 108 {
 109   SCM root;
 110   scm_root_state *root_state;
 111
 112   root_state = (scm_root_state *) scm_must_malloc (sizeof (scm_root_state),
 113                                                    "scm_make_root");
 114   if (SCM_ROOTP (parent))
 115     {
 116       memcpy (root_state, SCM_ROOT_STATE (parent), sizeof (scm_root_state));
 117       scm_copy_fluids (root_state);
 118       root_state->parent = parent;
 119     }
 120   else
 121     {
 122       root_state->parent = SCM_BOOL_F;
 123
 124       /* Initialize everything right now, in case a GC happens early.  */
 125       root_state->rootcont
 126         = root_state->dynwinds
 127         = root_state->continuation_stack
 128         = root_state->continuation_stack_ptr
 129         = root_state->progargs
 130         = root_state->exitval
 131         = root_state->cur_inp
 132         = root_state->cur_outp
 133         = root_state->cur_errp
 134         = root_state->def_inp
 135         = root_state->def_outp
 136         = root_state->def_errp
 137         = root_state->cur_loadp
 138         = root_state->fluids
 139         = root_state->handle
 140         = root_state->parent
 141         = SCM_BOOL_F;
 142     }
 143   SCM_REDEFER_INTS;
 144   SCM_NEWSMOB (root, scm_tc16_root, root_state);
 145   root_state->handle = root;
 146   SCM_REALLOW_INTS;
 147   return root;
 148 }
 149
 150 /* {call-with-dynamic-root}
 151  *
 152  * Suspending the current thread to evaluate a thunk on the
 153  * same C stack but under a new root.
 154  *
 155  * Calls to call-with-dynamic-root return exactly once (unless
 156  * the process is somehow exitted).  */
 157
 158 /* Some questions about cwdr:
 159
 160    Couldn't the body just be a closure?  Do we really need to pass
 161    args through to it?
 162
 163    The semantics are a lot like catch's; in fact, we call
 164    scm_internal_catch to take care of that part of things.  Wouldn't
 165    it be cleaner to say that uncaught throws just disappear into the
 166    ether (or print a message to stderr), and let the caller use catch
 167    themselves if they want to?
 168
 169    -JimB */
 170
 171 #if 0
 172 SCM scm_exitval;                /* INUM with return value */
 173 #endif
 174 static int n_dynamic_roots = 0;
 175
 176
 177 /* cwdr fills out both of these structures, and then passes a pointer
 178    to them through scm_internal_catch to the cwdr_body and
 179    cwdr_handler functions, to tell them how to behave and to get
 180    information back from them.
 181
 182    A cwdr is a lot like a catch, except there is no tag (all
 183    exceptions are caught), and the body procedure takes the arguments
 184    passed to cwdr as A1 and ARGS.  The handler is also special since
 185    it is not directly run from scm_internal_catch.  It is executed
 186    outside the new dynamic root. */
 187
 188 struct cwdr_body_data {
 189   /* Arguments to pass to the cwdr body function.  */
 190   SCM a1, args;
 191
 192   /* Scheme procedure to use as body of cwdr.  */
 193   SCM body_proc;
 194 };
 195
 196 struct cwdr_handler_data {
 197   /* Do we need to run the handler? */
 198   int run_handler;
 199
 200   /* The tag and args to pass it. */
 201   SCM tag, args;
 202 };
 203
 204
 205 /* Invoke the body of a cwdr, assuming that the throw handler has
 206    already been set up.  DATA points to a struct set up by cwdr that
 207    says what proc to call, and what args to apply it to.
 208
 209    With a little thought, we could replace this with scm_body_thunk,
 210    but I don't want to mess with that at the moment.  */
 211 static SCM
 212 cwdr_body (void *data)
 213 {
 214   struct cwdr_body_data *c = (struct cwdr_body_data *) data;
 215
 216   return scm_apply (c->body_proc, c->a1, c->args);
 217 }
 218
 219 /* Record the fact that the body of the cwdr has thrown.  Record
 220    enough information to invoke the handler later when the dynamic
 221    root has been deestablished.  */
 222
 223 static SCM
 224 cwdr_handler (void *data, SCM tag, SCM args)
 225 {
 226   struct cwdr_handler_data *c = (struct cwdr_handler_data *) data;
 227
 228   c->run_handler = 1;
 229   c->tag = tag;
 230   c->args = args;
 231   return SCM_UNSPECIFIED;
 232 }
 233
 234 /* This is the basic code for new root creation.
 235  *
 236  * WARNING!  The order of actions in this routine is in many ways
 237  * critical.  E. g., it is essential that an error doesn't leave Guile
 238  * in a messed up state.  */
 239
 240 SCM
 241 scm_internal_cwdr (scm_catch_body_t body, void *body_data,
 242                    scm_catch_handler_t handler, void *handler_data,
 243                    SCM_STACKITEM *stack_start)
 244 {
 245   int old_ints_disabled = scm_ints_disabled;
 246   SCM old_rootcont, old_winds;
 247   struct cwdr_handler_data my_handler_data;
 248   SCM answer;
 249
 250   /* Create a fresh root continuation.  */
 251   {
 252     SCM new_rootcont;
 253
 254     SCM_REDEFER_INTS;
 255     {
 256       scm_contregs *contregs = scm_must_malloc (sizeof (scm_contregs),
 257                                                 "inferior root continuation");
 258
 259       contregs->num_stack_items = 0;
 260       contregs->dynenv = SCM_EOL;
 261       contregs->base = stack_start;
 262       contregs->seq = ++n_dynamic_roots;
 263       contregs->throw_value = SCM_BOOL_F;
 264 #ifdef DEBUG_EXTENSIONS
 265       contregs->dframe = 0;
 266 #endif
 267       SCM_NEWSMOB (new_rootcont, scm_tc16_continuation, contregs);
 268     }
 269     old_rootcont = scm_rootcont;
 270     scm_rootcont = new_rootcont;
 271     SCM_REALLOW_INTS;
 272   }
 273
 274   /* Exit caller's dynamic state.
 275    */
 276   old_winds = scm_dynwinds;
 277   scm_dowinds (SCM_EOL, scm_ilength (scm_dynwinds));
 278 #ifdef DEBUG_EXTENSIONS
 279   SCM_DFRAME (old_rootcont) = scm_last_debug_frame;
 280   scm_last_debug_frame = 0;
 281 #endif
 282
 283   {
 284     my_handler_data.run_handler = 0;
 285     answer = scm_internal_catch (SCM_BOOL_T,
 286                                  body, body_data,
 287                                  cwdr_handler, &my_handler_data);
 288   }
 289
 290   scm_dowinds (old_winds, - scm_ilength (old_winds));
 291   SCM_REDEFER_INTS;
 292 #ifdef DEBUG_EXTENSIONS
 293   scm_last_debug_frame = SCM_DFRAME (old_rootcont);
 294 #endif
 295   scm_rootcont = old_rootcont;
 296   SCM_REALLOW_INTS;
 297   scm_ints_disabled = old_ints_disabled;
 298
 299   /* Now run the real handler iff the body did a throw. */
 300   if (my_handler_data.run_handler)
 301     return handler (handler_data, my_handler_data.tag, my_handler_data.args);
 302   else
 303     return answer;
 304 }
 305
 306 /* The original CWDR for invoking Scheme code with a Scheme handler. */
 307
 308 static SCM
 309 cwdr (SCM proc, SCM a1, SCM args, SCM handler, SCM_STACKITEM *stack_start)
 310 {
 311   struct cwdr_body_data c;
 312
 313   c.a1 = a1;
 314   c.args = args;
 315   c.body_proc = proc;
 316
 317   return scm_internal_cwdr (cwdr_body, &c,
 318                             scm_handle_by_proc, &handler,
 319                             stack_start);
 320 }
 321
 322 SCM_DEFINE (scm_call_with_dynamic_root, "call-with-dynamic-root", 2, 0, 0,
 323            (SCM thunk, SCM handler),
 324             "Evaluate @code{(thunk)} in a new dynamic context, returning its value.\n\n"
 325             "If an error occurs during evaluation, apply @var{handler} to the\n"
 326             "arguments to the throw, just as @code{throw} would.  If this happens,\n"
 327             "@var{handler} is called outside the scope of the new root -- it is\n"
 328             "called in the same dynamic context in which\n"
 329             "@code{call-with-dynamic-root} was evaluated.\n\n"
 330             "If @var{thunk} captures a continuation, the continuation is rooted at\n"
 331             "the call to @var{thunk}.  In particular, the call to\n"
 332             "@code{call-with-dynamic-root} is not captured.  Therefore,\n"
 333             "@code{call-with-dynamic-root} always returns at most one time.\n\n"
 334             "Before calling @var{thunk}, the dynamic-wind chain is un-wound back to\n"
 335             "the root and a new chain started for @var{thunk}.  Therefore, this call\n"
 336             "may not do what you expect:\n\n"
 337             "@example\n"
 338             ";; Almost certainly a bug:\n"
 339             "(with-output-to-port\n"
 340             " some-port\n\n"
 341             " (lambda ()\n"
 342             "   (call-with-dynamic-root\n"
 343             "    (lambda ()\n"
 344             "      (display 'fnord)\n"
 345             "      (newline))\n"
 346             "    (lambda (errcode) errcode))))\n"
 347             "@end example\n\n"
 348             "The problem is, on what port will @samp{fnord} be displayed?  You\n"
 349             "might expect that because of the @code{with-output-to-port} that\n"
 350             "it will be displayed on the port bound to @code{some-port}.  But it\n"
 351             "probably won't -- before evaluating the thunk, dynamic winds are\n"
 352             "unwound, including those created by @code{with-output-to-port}.\n"
 353             "So, the standard output port will have been re-set to its default value\n"
 354             "before @code{display} is evaluated.\n\n"
 355             "(This function was added to Guile mostly to help calls to functions in C\n"
 356             "libraries that can not tolerate non-local exits or calls that return\n"
 357             "multiple times.  If such functions call back to the interpreter, it should\n"
 358             "be under a new dynamic root.)")
 359 #define FUNC_NAME s_scm_call_with_dynamic_root
 360 {
 361   SCM_STACKITEM stack_place;
 362   return cwdr (thunk, SCM_EOL, SCM_EOL, handler, &stack_place);
 363 }
 364 #undef FUNC_NAME
 365
 366 SCM_DEFINE (scm_dynamic_root, "dynamic-root", 0, 0, 0,
 367            (),
 368             "Return an object representing the current dynamic root.\n\n"
 369             "These objects are only useful for comparison using @code{eq?}.\n"
 370             "They are currently represented as numbers, but your code should\n"
 371             "in no way depend on this.")
 372 #define FUNC_NAME s_scm_dynamic_root
 373 {
 374   return scm_ulong2num (SCM_SEQ (scm_root->rootcont));
 375 }
 376 #undef FUNC_NAME
 377
 378 SCM
 379 scm_apply_with_dynamic_root (SCM proc, SCM a1, SCM args, SCM handler)
 380 {
 381   SCM_STACKITEM stack_place;
 382   return cwdr (proc, a1, args, handler, &stack_place);
 383 }
 384
 385 \f
 386
 387 #if (SCM_DEBUG_DEPRECATED == 0)
 388
 389 /* Call thunk(closure) underneath a top-level error handler.
 390  * If an error occurs, pass the exitval through err_filter and return it.
 391  * If no error occurs, return the value of thunk.
 392  */
 393
 394 #ifdef _UNICOS
 395 typedef int setjmp_type;
 396 #else
 397 typedef long setjmp_type;
 398 #endif
 399
 400
 401 SCM
 402 scm_call_catching_errors (SCM (*thunk)(), SCM (*err_filter)(), void *closure)
 403 {
 404   SCM answer;
 405   setjmp_type i;
 406 #ifdef DEBUG_EXTENSIONS
 407   SCM_DFRAME (scm_rootcont) = scm_last_debug_frame;
 408 #endif
 409   i = setjmp (SCM_JMPBUF (scm_rootcont));
 410   scm_stack_checking_enabled_p = SCM_STACK_CHECKING_P;
 411   if (!i)
 412     {
 413       scm_gc_heap_lock = 0;
 414       answer = thunk (closure);
 415     }
 416   else
 417     {
 418       scm_gc_heap_lock = 1;
 419       answer = err_filter (scm_exitval, closure);
 420     }
 421   return answer;
 422 }
 423
 424 #endif  /* SCM_DEBUG_DEPRECATED == 0 */
 425
 426
 427 void
 428 scm_init_root ()
 429 {
 430   scm_tc16_root = scm_make_smob_type ("root", sizeof (struct scm_root_state));
 431   scm_set_smob_mark (scm_tc16_root, mark_root);
 432   scm_set_smob_print (scm_tc16_root, print_root);
 433
 434 #ifndef SCM_MAGIC_SNARFER
 435 #include "libguile/root.x"
 436 #endif
 437 }
 438
 439 /*
 440   Local Variables:
 441   c-file-style: "gnu"
 442   End:
 443 */