libguile/continuations.c

   1 /* Copyright (C) 1995,1996,1998,2000,2001,2004, 2006, 2008, 2009, 2010, 2011, 2012 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 "libguile/_scm.h"
  26
  27 #include <string.h>
  28 #include <stdio.h>
  29
  30 #include "libguile/async.h"
  31 #include "libguile/debug.h"
  32 #include "libguile/root.h"
  33 #include "libguile/stackchk.h"
  34 #include "libguile/smob.h"
  35 #include "libguile/ports.h"
  36 #include "libguile/dynwind.h"
  37 #include "libguile/eval.h"
  38 #include "libguile/vm.h"
  39 #include "libguile/instructions.h"
  40
  41 #include "libguile/validate.h"
  42 #include "libguile/continuations.h"
  43
  44 \f
  45
  46 static scm_t_bits tc16_continuation;
  47 #define SCM_CONTREGSP(x)        SCM_TYP16_PREDICATE (tc16_continuation, x)
  48
  49 #define SCM_CONTREGS(x)         ((scm_t_contregs *) SCM_SMOB_DATA_1 (x))
  50
  51 #define SCM_CONTINUATION_LENGTH(x) (SCM_CONTREGS (x)->num_stack_items)
  52 #define SCM_SET_CONTINUATION_LENGTH(x, n)\
  53    (SCM_CONTREGS (x)->num_stack_items = (n))
  54 #define SCM_JMPBUF(x)            ((SCM_CONTREGS (x))->jmpbuf)
  55 #define SCM_DYNENV(x)            ((SCM_CONTREGS (x))->dynenv)
  56 #define SCM_CONTINUATION_ROOT(x) ((SCM_CONTREGS (x))->root)
  57 #define SCM_DFRAME(x)            ((SCM_CONTREGS (x))->dframe)
  58
  59 \f
  60
  61 /* scm_i_make_continuation will return a procedure whose objcode contains an
  62    instruction to reinstate the continuation. Here, as in gsubr.c and smob.c, we
  63    define the form of that trampoline function.
  64  */
  65
  66 #ifdef WORDS_BIGENDIAN
  67 #define OBJCODE_HEADER(main,meta) 0, 0, 0, main, 0, 0, 0, meta+8
  68 #define META_HEADER(meta)         0, 0, 0, meta, 0, 0, 0, 0
  69 #else
  70 #define OBJCODE_HEADER(main,meta) main, 0, 0, 0, meta+8, 0, 0, 0
  71 #define META_HEADER(meta)         meta, 0, 0, 0, 0,      0, 0, 0
  72 #endif
  73
  74 #define OBJCODE_TAG SCM_MAKE_OBJCODE_TAG (SCM_OBJCODE_TYPE_STATIC, 0)
  75
  76 #if defined (SCM_ALIGNED) && 0
  77 #define SCM_DECLARE_STATIC_ALIGNED_ARRAY(type, sym)     \
  78 static const type sym[]
  79 #define SCM_STATIC_ALIGNED_ARRAY(alignment, type, sym)  \
  80 static SCM_ALIGNED (alignment) const type sym[]
  81 #define SCM_STATIC_OBJCODE(sym)                                         \
  82   SCM_DECLARE_STATIC_ALIGNED_ARRAY (scm_t_uint8, sym##__bytecode);      \
  83   SCM_STATIC_ALIGNED_ARRAY (8, scm_t_cell, sym##__cells) = {            \
  84     { SCM_PACK (OBJCODE_TAG), SCM_PACK (sym##__bytecode) },             \
  85     { SCM_BOOL_F, SCM_PACK (0) }                                        \
  86   };                                                                    \
  87   static const SCM sym = SCM_PACK (sym##__cells);                       \
  88   SCM_STATIC_ALIGNED_ARRAY (8, scm_t_uint8, sym##__bytecode)
  89 #else
  90 #define SCM_STATIC_OBJCODE(sym)                                         \
  91 static SCM sym;                                                         \
  92 static scm_t_uint8 *sym##_bytecode;                                     \
  93 SCM_SNARF_INIT(sym##_bytecode = scm_gc_malloc_pointerless (sizeof(sym##_bytecode__unaligned), "partial continuation stub"); \
  94                memcpy (sym##_bytecode, sym##_bytecode__unaligned, sizeof(sym##_bytecode__unaligned));) \
  95 SCM_SNARF_INIT(sym = scm_double_cell (OBJCODE_TAG,                      \
  96                                       (scm_t_bits)sym##_bytecode,       \
  97                                       SCM_UNPACK (SCM_BOOL_F),          \
  98                                       0);)                              \
  99 static const scm_t_uint8 sym##_bytecode__unaligned[]
 100 #endif
 101
 102
 103 SCM_STATIC_OBJCODE (cont_objcode) = {
 104   /* This code is the same as in gsubr.c, except we use continuation_call
 105      instead of subr_call. */
 106   OBJCODE_HEADER (8, 19),
 107   /* leave args on the stack */
 108   /* 0 */ scm_op_object_ref, 0, /* push scm_t_contregs smob */
 109   /* 2 */ scm_op_continuation_call, /* and longjmp (whee) */
 110   /* 3 */ scm_op_nop, /* pad to 8 bytes */
 111   /* 4 */ scm_op_nop, scm_op_nop, scm_op_nop, scm_op_nop,
 112   /* 8 */
 113
 114   /* We could put some meta-info to say that this proc is a continuation. Not sure
 115      how to do that, though. */
 116   META_HEADER (19),
 117   /* 0 */ scm_op_make_eol, /* bindings */
 118   /* 1 */ scm_op_make_eol, /* sources */
 119   /* 2 */ scm_op_make_int8, 0, scm_op_make_int8, 3, /* arity: from ip 0 to ip 3 */
 120   /* 6 */ scm_op_make_int8_0, /* the arity is 0 required args */
 121   /* 7 */ scm_op_make_int8_0, /* 0 optionals */
 122   /* 8 */ scm_op_make_true, /* and a rest arg */
 123   /* 9 */ scm_op_list, 0, 5, /* make a list of those 5 vals */
 124   /* 12 */ scm_op_list, 0, 1, /* and the arities will be a list of that one list */
 125   /* 15 */ scm_op_list, 0, 3, /* pack bindings, sources, and arities into list */
 126   /* 18 */ scm_op_return /* and return */
 127   /* 19 */
 128 };
 129
 130
 131 SCM_STATIC_OBJCODE (call_cc_objcode) = {
 132   /* Before Scheme's call/cc is compiled, eval.c will use this hand-coded
 133      call/cc. */
 134   OBJCODE_HEADER (8, 17),
 135   /* 0 */ scm_op_assert_nargs_ee, 0, 1, /* assert that nargs==1 */
 136   /* 3 */ scm_op_local_ref, 0, /* push the proc */
 137   /* 5 */ scm_op_tail_call_cc, /* and call/cc */
 138   /* 6 */ scm_op_nop, scm_op_nop, /* pad to 8 bytes */
 139   /* 8 */
 140
 141   META_HEADER (17),
 142   /* 0 */ scm_op_make_eol, /* bindings */
 143   /* 1 */ scm_op_make_eol, /* sources */
 144   /* 2 */ scm_op_make_int8, 3, scm_op_make_int8, 6, /* arity: from ip 0 to ip 6 */
 145   /* 6 */ scm_op_make_int8_1, /* the arity is 0 required args */
 146   /* 7 */ scm_op_list, 0, 3, /* make a list of those 5 vals */
 147   /* 10 */ scm_op_list, 0, 1, /* and the arities will be a list of that one list */
 148   /* 13 */ scm_op_list, 0, 3, /* pack bindings, sources, and arities into list */
 149   /* 16 */ scm_op_return /* and return */
 150   /* 17 */
 151 };
 152
 153
 154 static SCM
 155 make_continuation_trampoline (SCM contregs)
 156 {
 157   SCM ret = scm_make_program (cont_objcode,
 158                               scm_c_make_vector (1, contregs),
 159                               SCM_BOOL_F);
 160   SCM_SET_CELL_WORD_0 (ret,
 161                        SCM_CELL_WORD_0 (ret) | SCM_F_PROGRAM_IS_CONTINUATION);
 162
 163   return ret;
 164 }
 165
 166
 167 /* {Continuations}
 168  */
 169
 170
 171 static int
 172 continuation_print (SCM obj, SCM port, scm_print_state *state SCM_UNUSED)
 173 {
 174   scm_t_contregs *continuation = SCM_CONTREGS (obj);
 175
 176   scm_puts ("#<continuation ", port);
 177   scm_intprint (continuation->num_stack_items, 10, port);
 178   scm_puts (" @ ", port);
 179   scm_uintprint (SCM_SMOB_DATA_1 (obj), 16, port);
 180   scm_putc ('>', port);
 181   return 1;
 182 }
 183
 184 /* this may return more than once: the first time with the escape
 185    procedure, then subsequently with SCM_UNDEFINED (the vals already having been
 186    placed on the VM stack). */
 187 #define FUNC_NAME "scm_i_make_continuation"
 188 SCM
 189 scm_i_make_continuation (int *first, SCM vm, SCM vm_cont)
 190 {
 191   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 192   SCM cont;
 193   scm_t_contregs *continuation;
 194   long stack_size;
 195   SCM_STACKITEM * src;
 196
 197   SCM_FLUSH_REGISTER_WINDOWS;
 198   stack_size = scm_stack_size (thread->continuation_base);
 199   continuation = scm_gc_malloc (sizeof (scm_t_contregs)
 200                                 + (stack_size - 1) * sizeof (SCM_STACKITEM),
 201                                 "continuation");
 202   continuation->num_stack_items = stack_size;
 203   continuation->dynenv = scm_i_dynwinds ();
 204   continuation->root = thread->continuation_root;
 205   src = thread->continuation_base;
 206 #if ! SCM_STACK_GROWS_UP
 207   src -= stack_size;
 208 #endif
 209   continuation->offset = continuation->stack - src;
 210   memcpy (continuation->stack, src, sizeof (SCM_STACKITEM) * stack_size);
 211   continuation->vm = vm;
 212   continuation->vm_cont = vm_cont;
 213
 214   SCM_NEWSMOB (cont, tc16_continuation, continuation);
 215
 216   *first = !SCM_I_SETJMP (continuation->jmpbuf);
 217   if (*first)
 218     {
 219 #ifdef __ia64__
 220       continuation->backing_store_size =
 221         (char *) scm_ia64_ar_bsp(&continuation->jmpbuf.ctx)
 222         -
 223         (char *) thread->register_backing_store_base;
 224       continuation->backing_store = NULL;
 225       continuation->backing_store =
 226         scm_gc_malloc (continuation->backing_store_size,
 227                        "continuation backing store");
 228       memcpy (continuation->backing_store,
 229               (void *) thread->register_backing_store_base,
 230               continuation->backing_store_size);
 231 #endif /* __ia64__ */
 232       return make_continuation_trampoline (cont);
 233     }
 234   else
 235     return SCM_UNDEFINED;
 236 }
 237 #undef FUNC_NAME
 238
 239 SCM
 240 scm_i_call_with_current_continuation (SCM proc)
 241 {
 242   static SCM call_cc = SCM_BOOL_F;
 243
 244   if (scm_is_false (call_cc))
 245     call_cc = scm_make_program (call_cc_objcode, SCM_BOOL_F, SCM_BOOL_F);
 246
 247   return scm_call_1 (call_cc, proc);
 248 }
 249
 250 SCM
 251 scm_i_continuation_to_frame (SCM continuation)
 252 {
 253   SCM contregs;
 254   scm_t_contregs *cont;
 255
 256   contregs = scm_c_vector_ref (scm_program_objects (continuation), 0);
 257   cont = SCM_CONTREGS (contregs);
 258
 259   if (scm_is_true (cont->vm_cont))
 260     {
 261       struct scm_vm_cont *data = SCM_VM_CONT_DATA (cont->vm_cont);
 262       return scm_c_make_frame (cont->vm_cont,
 263                                data->fp + data->reloc,
 264                                data->sp + data->reloc,
 265                                data->ra,
 266                                data->reloc);
 267     }
 268   else
 269     return SCM_BOOL_F;
 270 }
 271
 272 SCM
 273 scm_i_contregs_vm (SCM contregs)
 274 {
 275   return SCM_CONTREGS (contregs)->vm;
 276 }
 277
 278 SCM
 279 scm_i_contregs_vm_cont (SCM contregs)
 280 {
 281   return SCM_CONTREGS (contregs)->vm_cont;
 282 }
 283
 284
 285 /* {Apply}
 286  */
 287
 288 /* Invoking a continuation proceeds as follows:
 289  *
 290  * - the stack is made large enough for the called continuation
 291  * - the old windchain is unwound down to the branching point
 292  * - the continuation stack is copied into place
 293  * - the windchain is rewound up to the continuation's context
 294  * - the continuation is invoked via longjmp (or setcontext)
 295  *
 296  * This order is important so that unwind and rewind handlers are run
 297  * with their correct stack.
 298  */
 299
 300 static void scm_dynthrow (SCM);
 301
 302 /* Grow the stack by a fixed amount to provide space to copy in the
 303  * continuation.  Possibly this function has to be called several times
 304  * recursively before enough space is available.  Make sure the compiler does
 305  * not optimize the growth array away by storing it's address into a global
 306  * variable.
 307  */
 308
 309 static scm_t_bits scm_i_dummy;
 310
 311 static void
 312 grow_stack (SCM cont)
 313 {
 314   scm_t_bits growth[100];
 315
 316   scm_i_dummy = (scm_t_bits) growth;
 317   scm_dynthrow (cont);
 318 }
 319
 320
 321 /* Copy the continuation stack into the current stack.  Calling functions from
 322  * within this function is safe, since only stack frames below this function's
 323  * own frame are overwritten.  Thus, memcpy can be used for best performance.
 324  */
 325
 326 typedef struct {
 327   scm_t_contregs *continuation;
 328   SCM_STACKITEM *dst;
 329 } copy_stack_data;
 330
 331 static void
 332 copy_stack (void *data)
 333 {
 334   copy_stack_data *d = (copy_stack_data *)data;
 335   memcpy (d->dst, d->continuation->stack,
 336           sizeof (SCM_STACKITEM) * d->continuation->num_stack_items);
 337 #ifdef __ia64__
 338   SCM_I_CURRENT_THREAD->pending_rbs_continuation = d->continuation;
 339 #endif
 340 }
 341
 342 static void
 343 copy_stack_and_call (scm_t_contregs *continuation,
 344                      SCM_STACKITEM * dst)
 345 {
 346   long delta;
 347   copy_stack_data data;
 348
 349   delta = scm_ilength (scm_i_dynwinds ()) - scm_ilength (continuation->dynenv);
 350   data.continuation = continuation;
 351   data.dst = dst;
 352   scm_i_dowinds (continuation->dynenv, delta, copy_stack, &data);
 353
 354   SCM_I_LONGJMP (continuation->jmpbuf, 1);
 355 }
 356
 357 #ifdef __ia64__
 358 void
 359 scm_ia64_longjmp (scm_i_jmp_buf *JB, int VAL)
 360 {
 361   scm_i_thread *t = SCM_I_CURRENT_THREAD;
 362
 363   if (t->pending_rbs_continuation)
 364     {
 365       memcpy (t->register_backing_store_base,
 366               t->pending_rbs_continuation->backing_store,
 367               t->pending_rbs_continuation->backing_store_size);
 368       t->pending_rbs_continuation = NULL;
 369     }
 370   setcontext (&JB->ctx);
 371 }
 372 #endif
 373
 374 /* Call grow_stack until the stack space is large enough, then, as the current
 375  * stack frame might get overwritten, let copy_stack_and_call perform the
 376  * actual copying and continuation calling.
 377  */
 378 static void
 379 scm_dynthrow (SCM cont)
 380 {
 381   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 382   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 383   SCM_STACKITEM *dst = thread->continuation_base;
 384   SCM_STACKITEM stack_top_element;
 385
 386   if (thread->critical_section_level)
 387     {
 388       fprintf (stderr, "continuation invoked from within critical section.\n");
 389       abort ();
 390     }
 391
 392 #if SCM_STACK_GROWS_UP
 393   if (dst + continuation->num_stack_items >= &stack_top_element)
 394     grow_stack (cont);
 395 #else
 396   dst -= continuation->num_stack_items;
 397   if (dst <= &stack_top_element)
 398     grow_stack (cont);
 399 #endif /* def SCM_STACK_GROWS_UP */
 400
 401   SCM_FLUSH_REGISTER_WINDOWS;
 402   copy_stack_and_call (continuation, dst);
 403 }
 404
 405
 406 void
 407 scm_i_check_continuation (SCM cont)
 408 {
 409   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 410   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 411
 412   if (!scm_is_eq (continuation->root, thread->continuation_root))
 413     scm_misc_error
 414       ("%continuation-call",
 415        "invoking continuation would cross continuation barrier: ~A",
 416        scm_list_1 (cont));
 417 }
 418
 419 void
 420 scm_i_reinstate_continuation (SCM cont)
 421 {
 422   scm_dynthrow (cont);
 423 }
 424
 425 SCM
 426 scm_i_with_continuation_barrier (scm_t_catch_body body,
 427                                  void *body_data,
 428                                  scm_t_catch_handler handler,
 429                                  void *handler_data,
 430                                  scm_t_catch_handler pre_unwind_handler,
 431                                  void *pre_unwind_handler_data)
 432 {
 433   SCM_STACKITEM stack_item;
 434   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 435   SCM old_controot;
 436   SCM_STACKITEM *old_contbase;
 437   SCM result;
 438
 439   /* Establish a fresh continuation root.
 440    */
 441   old_controot = thread->continuation_root;
 442   old_contbase = thread->continuation_base;
 443   thread->continuation_root = scm_cons (thread->handle, old_controot);
 444   thread->continuation_base = &stack_item;
 445
 446   /* Call FUNC inside a catch all.  This is now guaranteed to return
 447      directly and exactly once.
 448   */
 449   result = scm_c_catch (SCM_BOOL_T,
 450                         body, body_data,
 451                         handler, handler_data,
 452                         pre_unwind_handler, pre_unwind_handler_data);
 453
 454   /* Return to old continuation root.
 455    */
 456   thread->continuation_base = old_contbase;
 457   thread->continuation_root = old_controot;
 458
 459   return result;
 460 }
 461
 462 \f
 463
 464 static int
 465 should_print_backtrace (SCM tag, SCM stack)
 466 {
 467   return SCM_BACKTRACE_P
 468     && scm_is_true (stack)
 469     && scm_initialized_p
 470     /* It's generally not useful to print backtraces for errors reading
 471        or expanding code in these fallback catch statements. */
 472     && !scm_is_eq (tag, scm_from_latin1_symbol ("read-error"))
 473     && !scm_is_eq (tag, scm_from_latin1_symbol ("syntax-error"));
 474 }
 475
 476 static void
 477 print_exception_and_backtrace (SCM port, SCM tag, SCM args)
 478 {
 479   SCM stack, frame;
 480
 481   /* We get here via a throw to a catch-all.  In that case there is the
 482      throw frame active, and this catch closure, so narrow by two
 483      frames.  */
 484   stack = scm_make_stack (SCM_BOOL_T, scm_list_1 (scm_from_int (2)));
 485   frame = scm_is_true (stack) ? scm_stack_ref (stack, SCM_INUM0) : SCM_BOOL_F;
 486
 487   if (should_print_backtrace (tag, stack))
 488     {
 489       scm_puts ("Backtrace:\n", port);
 490       scm_display_backtrace_with_highlights (stack, port,
 491                                              SCM_BOOL_F, SCM_BOOL_F,
 492                                              SCM_EOL);
 493       scm_newline (port);
 494     }
 495
 496   scm_print_exception (port, frame, tag, args);
 497 }
 498
 499 \f
 500
 501 struct c_data {
 502   void *(*func) (void *);
 503   void *data;
 504   void *result;
 505 };
 506
 507 static SCM
 508 c_body (void *d)
 509 {
 510   struct c_data *data = (struct c_data *)d;
 511   data->result = data->func (data->data);
 512   return SCM_UNSPECIFIED;
 513 }
 514
 515 static SCM
 516 c_handler (void *d, SCM tag, SCM args)
 517 {
 518   struct c_data *data;
 519
 520   /* If TAG is `quit', exit() the process.  */
 521   if (scm_is_eq (tag, scm_from_latin1_symbol ("quit")))
 522     exit (scm_exit_status (args));
 523
 524   data = (struct c_data *)d;
 525   data->result = NULL;
 526   return SCM_UNSPECIFIED;
 527 }
 528
 529 static SCM
 530 pre_unwind_handler (void *error_port, SCM tag, SCM args)
 531 {
 532   /* Print the exception unless TAG is  `quit'.  */
 533   if (!scm_is_eq (tag, scm_from_latin1_symbol ("quit")))
 534     print_exception_and_backtrace (PTR2SCM (error_port), tag, args);
 535
 536   return SCM_UNSPECIFIED;
 537 }
 538
 539 void *
 540 scm_c_with_continuation_barrier (void *(*func) (void *), void *data)
 541 {
 542   struct c_data c_data;
 543   c_data.func = func;
 544   c_data.data = data;
 545   scm_i_with_continuation_barrier (c_body, &c_data,
 546                                    c_handler, &c_data,
 547                                    pre_unwind_handler,
 548                                    SCM2PTR (scm_current_error_port ()));
 549   return c_data.result;
 550 }
 551
 552 struct scm_data {
 553   SCM proc;
 554 };
 555
 556 static SCM
 557 scm_body (void *d)
 558 {
 559   struct scm_data *data = (struct scm_data *)d;
 560   return scm_call_0 (data->proc);
 561 }
 562
 563 static SCM
 564 scm_handler (void *d, SCM tag, SCM args)
 565 {
 566   /* Print a message.  Note that if TAG is `quit', this will exit() the
 567      process.  */
 568   scm_handle_by_message_noexit (NULL, tag, args);
 569
 570   return SCM_BOOL_F;
 571 }
 572
 573 SCM_DEFINE (scm_with_continuation_barrier, "with-continuation-barrier", 1,0,0,
 574             (SCM proc),
 575 "Call @var{proc} and return its result.  Do not allow the invocation of\n"
 576 "continuations that would leave or enter the dynamic extent of the call\n"
 577 "to @code{with-continuation-barrier}.  Such an attempt causes an error\n"
 578 "to be signaled.\n"
 579 "\n"
 580 "Throws (such as errors) that are not caught from within @var{proc} are\n"
 581 "caught by @code{with-continuation-barrier}.  In that case, a short\n"
 582 "message is printed to the current error port and @code{#f} is returned.\n"
 583 "\n"
 584 "Thus, @code{with-continuation-barrier} returns exactly once.\n")
 585 #define FUNC_NAME s_scm_with_continuation_barrier
 586 {
 587   struct scm_data scm_data;
 588   scm_data.proc = proc;
 589   return scm_i_with_continuation_barrier (scm_body, &scm_data,
 590                                           scm_handler, &scm_data,
 591                                           pre_unwind_handler,
 592                                           SCM2PTR (scm_current_error_port ()));
 593 }
 594 #undef FUNC_NAME
 595
 596 void
 597 scm_init_continuations ()
 598 {
 599   tc16_continuation = scm_make_smob_type ("continuation", 0);
 600   scm_set_smob_print (tc16_continuation, continuation_print);
 601 #include "libguile/continuations.x"
 602 }
 603
 604 /*
 605   Local Variables:
 606   c-file-style: "gnu"
 607   End:
 608 */