libguile/throw.c

   1 /* Copyright (C) 1995,1996,1997,1998,2000,2001, 2003, 2004, 2006, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
   2  *
   3  * This library is free software; you can redistribute it and/or
   4  * modify it under the terms of the GNU Lesser General Public License
   5  * as published by the Free Software Foundation; either version 3 of
   6  * the License, or (at your option) any later version.
   7  *
   8  * This library is distributed in the hope that it will be useful, but
   9  * WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * Lesser General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU Lesser General Public
  14  * License along with this library; if not, write to the Free Software
  15  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  16  * 02110-1301 USA
  17  */
  18
  19
  20 \f
  21 #ifdef HAVE_CONFIG_H
  22 # include <config.h>
  23 #endif
  24
  25 #include <stdio.h>
  26 #include <unistdio.h>
  27 #include "libguile/_scm.h"
  28 #include "libguile/smob.h"
  29 #include "libguile/eval.h"
  30 #include "libguile/eq.h"
  31 #include "libguile/control.h"
  32 #include "libguile/deprecation.h"
  33 #include "libguile/backtrace.h"
  34 #include "libguile/debug.h"
  35 #include "libguile/stackchk.h"
  36 #include "libguile/stacks.h"
  37 #include "libguile/fluids.h"
  38 #include "libguile/ports.h"
  39 #include "libguile/validate.h"
  40 #include "libguile/vm.h"
  41 #include "libguile/throw.h"
  42 #include "libguile/init.h"
  43 #include "libguile/strings.h"
  44
  45 #include "libguile/private-options.h"
  46
  47
  48 /* Pleasantly enough, the guts of catch are defined in Scheme, in terms of
  49    prompt, abort, and the %exception-handler fluid. This file just provides
  50    shims so that it's easy to have catch functionality from C.
  51
  52    All of these function names and prototypes carry a fair bit of historical
  53    baggage. */
  54
  55
  56 #define CACHE_VAR(var,name)                                             \
  57   static SCM var = SCM_BOOL_F;                                          \
  58   if (scm_is_false (var))                                               \
  59     {                                                                   \
  60       var = scm_module_variable (scm_the_root_module (),                \
  61                                  scm_from_latin1_symbol (name));        \
  62       if (scm_is_false (var))                                           \
  63         abort ();                                                       \
  64     }
  65
  66 \f
  67
  68 SCM
  69 scm_catch (SCM key, SCM thunk, SCM handler)
  70 {
  71   CACHE_VAR (var, "catch");
  72
  73   return scm_call_3 (scm_variable_ref (var), key, thunk, handler);
  74 }
  75
  76 SCM
  77 scm_catch_with_pre_unwind_handler (SCM key, SCM thunk, SCM handler,
  78                                    SCM pre_unwind_handler)
  79 {
  80   if (SCM_UNBNDP (pre_unwind_handler))
  81     return scm_catch (key, thunk, handler);
  82   else
  83     {
  84       CACHE_VAR (var, "catch");
  85
  86       return scm_call_4 (scm_variable_ref (var), key, thunk, handler,
  87                          pre_unwind_handler);
  88     }
  89 }
  90
  91 SCM
  92 scm_with_throw_handler (SCM key, SCM thunk, SCM handler)
  93 {
  94   CACHE_VAR (var, "with-throw-handler");
  95
  96   return scm_call_3 (scm_variable_ref (var), key, thunk, handler);
  97 }
  98
  99 SCM
 100 scm_throw (SCM key, SCM args)
 101 {
 102   CACHE_VAR (var, "throw");
 103
 104   return scm_apply_1 (scm_variable_ref (var), key, args);
 105 }
 106
 107 \f
 108
 109 /* Now some support for C bodies and catch handlers */
 110
 111 static scm_t_bits tc16_catch_closure;
 112
 113 enum {
 114   CATCH_CLOSURE_BODY,
 115   CATCH_CLOSURE_HANDLER
 116 };
 117
 118 static SCM
 119 make_catch_body_closure (scm_t_catch_body body, void *body_data)
 120 {
 121   SCM ret;
 122   SCM_NEWSMOB2 (ret, tc16_catch_closure, body, body_data);
 123   SCM_SET_SMOB_FLAGS (ret, CATCH_CLOSURE_BODY);
 124   return ret;
 125 }
 126
 127 static SCM
 128 make_catch_handler_closure (scm_t_catch_handler handler, void *handler_data)
 129 {
 130   SCM ret;
 131   SCM_NEWSMOB2 (ret, tc16_catch_closure, handler, handler_data);
 132   SCM_SET_SMOB_FLAGS (ret, CATCH_CLOSURE_HANDLER);
 133   return ret;
 134 }
 135
 136 static SCM
 137 apply_catch_closure (SCM clo, SCM args)
 138 {
 139   void *data = (void*)SCM_SMOB_DATA_2 (clo);
 140
 141   switch (SCM_SMOB_FLAGS (clo))
 142     {
 143     case CATCH_CLOSURE_BODY:
 144       {
 145         scm_t_catch_body body = (void*)SCM_SMOB_DATA (clo);
 146         return body (data);
 147       }
 148     case CATCH_CLOSURE_HANDLER:
 149       {
 150         scm_t_catch_handler handler = (void*)SCM_SMOB_DATA (clo);
 151         return handler (data, scm_car (args), scm_cdr (args));
 152       }
 153     default:
 154       abort ();
 155     }
 156 }
 157
 158 /* TAG is the catch tag.  Typically, this is a symbol, but this
 159    function doesn't actually care about that.
 160
 161    BODY is a pointer to a C function which runs the body of the catch;
 162    this is the code you can throw from.  We call it like this:
 163       BODY (BODY_DATA)
 164    where:
 165       BODY_DATA is just the BODY_DATA argument we received; we pass it
 166          through to BODY as its first argument.  The caller can make
 167          BODY_DATA point to anything useful that BODY might need.
 168
 169    HANDLER is a pointer to a C function to deal with a throw to TAG,
 170    should one occur.  We call it like this:
 171       HANDLER (HANDLER_DATA, THROWN_TAG, THROW_ARGS)
 172    where
 173       HANDLER_DATA is the HANDLER_DATA argument we recevied; it's the
 174          same idea as BODY_DATA above.
 175       THROWN_TAG is the tag that the user threw to; usually this is
 176          TAG, but it could be something else if TAG was #t (i.e., a
 177          catch-all), or the user threw to a jmpbuf.
 178       THROW_ARGS is the list of arguments the user passed to the THROW
 179          function, after the tag.
 180
 181    BODY_DATA is just a pointer we pass through to BODY.  HANDLER_DATA
 182    is just a pointer we pass through to HANDLER.  We don't actually
 183    use either of those pointers otherwise ourselves.  The idea is
 184    that, if our caller wants to communicate something to BODY or
 185    HANDLER, it can pass a pointer to it as MUMBLE_DATA, which BODY and
 186    HANDLER can then use.  Think of it as a way to make BODY and
 187    HANDLER closures, not just functions; MUMBLE_DATA points to the
 188    enclosed variables.
 189
 190    Of course, it's up to the caller to make sure that any data a
 191    MUMBLE_DATA needs is protected from GC.  A common way to do this is
 192    to make MUMBLE_DATA a pointer to data stored in an automatic
 193    structure variable; since the collector must scan the stack for
 194    references anyway, this assures that any references in MUMBLE_DATA
 195    will be found.  */
 196
 197 SCM
 198 scm_c_catch (SCM tag,
 199              scm_t_catch_body body, void *body_data,
 200              scm_t_catch_handler handler, void *handler_data,
 201              scm_t_catch_handler pre_unwind_handler, void *pre_unwind_handler_data)
 202 {
 203   SCM sbody, shandler, spre_unwind_handler;
 204
 205   sbody = make_catch_body_closure (body, body_data);
 206   shandler = make_catch_handler_closure (handler, handler_data);
 207   if (pre_unwind_handler)
 208     spre_unwind_handler = make_catch_handler_closure (pre_unwind_handler,
 209                                                       pre_unwind_handler_data);
 210   else
 211     spre_unwind_handler = SCM_UNDEFINED;
 212
 213   return scm_catch_with_pre_unwind_handler (tag, sbody, shandler,
 214                                             spre_unwind_handler);
 215 }
 216
 217 SCM
 218 scm_internal_catch (SCM tag,
 219                     scm_t_catch_body body, void *body_data,
 220                     scm_t_catch_handler handler, void *handler_data)
 221 {
 222   return scm_c_catch (tag,
 223                       body, body_data,
 224                       handler, handler_data,
 225                       NULL, NULL);
 226 }
 227
 228
 229 SCM
 230 scm_c_with_throw_handler (SCM tag,
 231                           scm_t_catch_body body,
 232                           void *body_data,
 233                           scm_t_catch_handler handler,
 234                           void *handler_data,
 235                           int lazy_catch_p)
 236 {
 237   SCM sbody, shandler;
 238
 239   if (lazy_catch_p)
 240     scm_c_issue_deprecation_warning
 241       ("The LAZY_CATCH_P argument to `scm_c_with_throw_handler' is no longer.\n"
 242        "supported. Instead the handler will be invoked from within the dynamic\n"
 243        "context of the corresponding `throw'.\n"
 244        "\nTHIS COULD CHANGE YOUR PROGRAM'S BEHAVIOR.\n\n"
 245        "Please modify your program to pass 0 as the LAZY_CATCH_P argument,\n"
 246        "and adapt it (if necessary) to expect to be within the dynamic context\n"
 247        "of the throw.");
 248
 249   sbody = make_catch_body_closure (body, body_data);
 250   shandler = make_catch_handler_closure (handler, handler_data);
 251
 252   return scm_with_throw_handler (tag, sbody, shandler);
 253 }
 254
 255 \f
 256 /* body and handler functions for use with any of the above catch variants */
 257
 258 /* This is a body function you can pass to scm_internal_catch if you
 259    want the body to be like Scheme's `catch' --- a thunk.
 260
 261    BODY_DATA is a pointer to a scm_body_thunk_data structure, which
 262    contains the Scheme procedure to invoke as the body, and the tag
 263    we're catching.  */
 264
 265 SCM
 266 scm_body_thunk (void *body_data)
 267 {
 268   struct scm_body_thunk_data *c = (struct scm_body_thunk_data *) body_data;
 269
 270   return scm_call_0 (c->body_proc);
 271 }
 272
 273
 274 /* This is a handler function you can pass to scm_internal_catch if
 275    you want the handler to act like Scheme's catch: (throw TAG ARGS ...)
 276    applies a handler procedure to (TAG ARGS ...).
 277
 278    If the user does a throw to this catch, this function runs a
 279    handler procedure written in Scheme.  HANDLER_DATA is a pointer to
 280    an SCM variable holding the Scheme procedure object to invoke.  It
 281    ought to be a pointer to an automatic variable (i.e., one living on
 282    the stack), or the procedure object should be otherwise protected
 283    from GC.  */
 284 SCM
 285 scm_handle_by_proc (void *handler_data, SCM tag, SCM throw_args)
 286 {
 287   SCM *handler_proc_p = (SCM *) handler_data;
 288
 289   return scm_apply_1 (*handler_proc_p, tag, throw_args);
 290 }
 291
 292 /* SCM_HANDLE_BY_PROC_CATCHING_ALL is like SCM_HANDLE_BY_PROC but
 293    catches all throws that the handler might emit itself.  The handler
 294    used for these `secondary' throws is SCM_HANDLE_BY_MESSAGE_NO_EXIT.  */
 295
 296 struct hbpca_data {
 297   SCM proc;
 298   SCM args;
 299 };
 300
 301 static SCM
 302 hbpca_body (void *body_data)
 303 {
 304   struct hbpca_data *data = (struct hbpca_data *)body_data;
 305   return scm_apply_0 (data->proc, data->args);
 306 }
 307
 308 SCM
 309 scm_handle_by_proc_catching_all (void *handler_data, SCM tag, SCM throw_args)
 310 {
 311   SCM *handler_proc_p = (SCM *) handler_data;
 312   struct hbpca_data data;
 313   data.proc = *handler_proc_p;
 314   data.args = scm_cons (tag, throw_args);
 315
 316   return scm_internal_catch (SCM_BOOL_T,
 317                              hbpca_body, &data,
 318                              scm_handle_by_message_noexit, NULL);
 319 }
 320
 321 /* Derive the an exit status from the arguments to (quit ...).  */
 322 int
 323 scm_exit_status (SCM args)
 324 {
 325   if (!SCM_NULL_OR_NIL_P (args))
 326     {
 327       SCM cqa = SCM_CAR (args);
 328
 329       if (scm_is_integer (cqa))
 330         return (scm_to_int (cqa));
 331       else if (scm_is_false (cqa))
 332         return 1;
 333     }
 334   return 0;
 335 }
 336
 337
 338 static int
 339 should_print_backtrace (SCM tag, SCM stack)
 340 {
 341   return SCM_BACKTRACE_P
 342     && scm_is_true (stack)
 343     && scm_initialized_p
 344     /* It's generally not useful to print backtraces for errors reading
 345        or expanding code in these fallback catch statements. */
 346     && !scm_is_eq (tag, scm_from_latin1_symbol ("read-error"))
 347     && !scm_is_eq (tag, scm_from_latin1_symbol ("syntax-error"));
 348 }
 349
 350 static void
 351 handler_message (void *handler_data, SCM tag, SCM args)
 352 {
 353   SCM p, stack, frame;
 354
 355   p = scm_current_error_port ();
 356   /* Usually we get here via a throw to a catch-all.  In that case
 357      there is the throw frame active, and the catch closure, so narrow by
 358      two frames.  It is possible for a user to invoke
 359      scm_handle_by_message directly, though, so it could be this
 360      narrows too much.  We'll have to see how this works out in
 361      practice.  */
 362   stack = scm_make_stack (SCM_BOOL_T, scm_list_1 (scm_from_int (2)));
 363   frame = scm_is_true (stack) ? scm_stack_ref (stack, SCM_INUM0) : SCM_BOOL_F;
 364
 365   if (should_print_backtrace (tag, stack))
 366     {
 367       scm_puts ("Backtrace:\n", p);
 368       scm_display_backtrace_with_highlights (stack, p,
 369                                              SCM_BOOL_F, SCM_BOOL_F,
 370                                              SCM_EOL);
 371       scm_newline (p);
 372     }
 373
 374   scm_print_exception (p, frame, tag, args);
 375 }
 376
 377
 378 /* This is a handler function to use if you want scheme to print a
 379    message and die.  Useful for dealing with throws to uncaught keys
 380    at the top level.
 381
 382    At boot time, we establish a catch-all that uses this as its handler.
 383    1) If the user wants something different, they can use (catch #t
 384    ...) to do what they like.
 385    2) Outside the context of a read-eval-print loop, there isn't
 386    anything else good to do; libguile should not assume the existence
 387    of a read-eval-print loop.
 388    3) Given that we shouldn't do anything complex, it's much more
 389    robust to do it in C code.
 390
 391    HANDLER_DATA, if non-zero, is assumed to be a char * pointing to a
 392    message header to print; if zero, we use "guile" instead.  That
 393    text is followed by a colon, then the message described by ARGS.  */
 394
 395 /* Dirk:FIXME:: The name of the function should make clear that the
 396  * application gets terminated.
 397  */
 398
 399 SCM
 400 scm_handle_by_message (void *handler_data, SCM tag, SCM args)
 401 {
 402   if (scm_is_true (scm_eq_p (tag, scm_from_latin1_symbol ("quit"))))
 403     exit (scm_exit_status (args));
 404
 405   handler_message (handler_data, tag, args);
 406   scm_i_pthread_exit (NULL);
 407
 408   /* this point not reached, but suppress gcc warning about no return value
 409      in case scm_i_pthread_exit isn't marked as "noreturn" (which seemed not
 410      to be the case on cygwin for instance) */
 411   return SCM_BOOL_F;
 412 }
 413
 414
 415 /* This is just like scm_handle_by_message, but it doesn't exit; it
 416    just returns #f.  It's useful in cases where you don't really know
 417    enough about the body to handle things in a better way, but don't
 418    want to let throws fall off the bottom of the wind list.  */
 419 SCM
 420 scm_handle_by_message_noexit (void *handler_data, SCM tag, SCM args)
 421 {
 422   if (scm_is_true (scm_eq_p (tag, scm_from_latin1_symbol ("quit"))))
 423     exit (scm_exit_status (args));
 424
 425   handler_message (handler_data, tag, args);
 426
 427   return SCM_BOOL_F;
 428 }
 429
 430
 431 SCM
 432 scm_handle_by_throw (void *handler_data SCM_UNUSED, SCM tag, SCM args)
 433 {
 434   scm_ithrow (tag, args, 1);
 435   return SCM_UNSPECIFIED;  /* never returns */
 436 }
 437
 438 SCM
 439 scm_ithrow (SCM key, SCM args, int no_return SCM_UNUSED)
 440 {
 441   return scm_throw (key, args);
 442 }
 443
 444 /* Unfortunately we have to support catch and throw before boot-9 has, um,
 445    booted. So here are lame versions, which will get replaced with their scheme
 446    equivalents. */
 447
 448 SCM_SYMBOL (sym_pre_init_catch_tag, "%pre-init-catch-tag");
 449
 450 static SCM
 451 pre_init_catch (SCM tag, SCM thunk, SCM handler, SCM pre_unwind_handler)
 452 {
 453   SCM vm, prompt, res;
 454
 455   /* Only handle catch-alls without pre-unwind handlers */
 456   if (!SCM_UNBNDP (pre_unwind_handler))
 457     abort ();
 458   if (scm_is_false (scm_eqv_p (tag, SCM_BOOL_T)))
 459     abort ();
 460
 461   vm = scm_the_vm ();
 462   prompt = scm_c_make_prompt (sym_pre_init_catch_tag,
 463                               SCM_VM_DATA (vm)->fp, SCM_VM_DATA (vm)->sp,
 464                               SCM_VM_DATA (vm)->ip, 1, -1, scm_i_dynwinds ());
 465   scm_i_set_dynwinds (scm_cons (prompt, SCM_PROMPT_DYNWINDS (prompt)));
 466
 467   if (SCM_PROMPT_SETJMP (prompt))
 468     {
 469       /* nonlocal exit */
 470       SCM args = scm_i_prompt_pop_abort_args_x (vm);
 471       /* cdr past the continuation */
 472       return scm_apply_0 (handler, scm_cdr (args));
 473     }
 474
 475   res = scm_call_0 (thunk);
 476   scm_i_set_dynwinds (scm_cdr (scm_i_dynwinds ()));
 477
 478   return res;
 479 }
 480
 481 static int
 482 find_pre_init_catch (void)
 483 {
 484   SCM winds;
 485
 486   /* Search the wind list for an appropriate prompt.
 487      "Waiter, please bring us the wind list." */
 488   for (winds = scm_i_dynwinds (); scm_is_pair (winds); winds = SCM_CDR (winds))
 489     if (SCM_PROMPT_P (SCM_CAR (winds))
 490         && scm_is_eq (SCM_PROMPT_TAG (SCM_CAR (winds)), sym_pre_init_catch_tag))
 491       return 1;
 492
 493   return 0;
 494 }
 495
 496 static SCM
 497 pre_init_throw (SCM k, SCM args)
 498 {
 499   if (find_pre_init_catch ())
 500     return scm_at_abort (sym_pre_init_catch_tag, scm_cons (k, args));
 501   else
 502     {
 503       static int error_printing_error = 0;
 504       static int error_printing_fallback = 0;
 505
 506       if (error_printing_fallback)
 507         fprintf (stderr, "\nFailed to print exception.\n");
 508       else if (error_printing_error)
 509         {
 510           fprintf (stderr, "\nError while printing exception:\n");
 511           error_printing_fallback = 1;
 512           fprintf (stderr, "Key: ");
 513           scm_write (k, scm_current_error_port ());
 514           fprintf (stderr, ", args: ");
 515           scm_write (args, scm_current_error_port ());
 516           scm_newline (scm_current_error_port ());
 517         }
 518       else
 519         {
 520           fprintf (stderr, "Throw without catch before boot:\n");
 521           error_printing_error = 1;
 522           scm_handle_by_message_noexit (NULL, k, args);
 523         }
 524
 525       fprintf (stderr, "Aborting.\n");
 526       abort ();
 527       return SCM_BOOL_F; /* not reached */
 528     }
 529 }
 530
 531 void
 532 scm_init_throw ()
 533 {
 534   tc16_catch_closure = scm_make_smob_type ("catch-closure", 0);
 535   scm_set_smob_apply (tc16_catch_closure, apply_catch_closure, 0, 0, 1);
 536
 537   scm_c_define ("catch", scm_c_make_gsubr ("catch", 3, 1, 0, pre_init_catch));
 538   scm_c_define ("throw", scm_c_make_gsubr ("throw", 1, 0, 1, pre_init_throw));
 539
 540 #include "libguile/throw.x"
 541 }
 542
 543 /*
 544   Local Variables:
 545   c-file-style: "gnu"
 546   End:
 547 */