libguile/continuations.c

   1 /* Copyright (C) 1995,1996,1998,2000,2001,2004, 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 "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 ALIGN_PTR(type,p,align) (type*)(ROUND_UP (((scm_t_bits)p), align))
  75
  76 #ifdef SCM_ALIGNED
  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 #else
  82 #define SCM_DECLARE_STATIC_ALIGNED_ARRAY(type, sym)     \
  83 static type *sym
  84 #define SCM_STATIC_ALIGNED_ARRAY(alignment, type, sym)                  \
  85 SCM_SNARF_INIT(sym = scm_malloc_pointerless (sizeof(sym##__unaligned)); \
  86                memcpy (sym, sym##__unaligned, sizeof(sym##__unaligned));) \
  87 static type *sym = NULL;                                                \
  88 static const type sym##__unaligned[]
  89 #endif
  90
  91 #define STATIC_OBJCODE_TAG                                      \
  92   SCM_PACK (SCM_MAKE_OBJCODE_TAG (SCM_OBJCODE_TYPE_STATIC, 0))
  93
  94 #define SCM_STATIC_OBJCODE(sym)                                         \
  95   SCM_DECLARE_STATIC_ALIGNED_ARRAY (scm_t_uint8, sym##__bytecode);      \
  96   SCM_STATIC_ALIGNED_ARRAY (8, scm_t_cell, sym##__cells) = {            \
  97     { STATIC_OBJCODE_TAG, SCM_PACK (sym##__bytecode) },                 \
  98     { SCM_BOOL_F, SCM_PACK (0) }                                        \
  99   };                                                                    \
 100   static const SCM sym = SCM_PACK (sym##__cells);                       \
 101   SCM_STATIC_ALIGNED_ARRAY (8, scm_t_uint8, sym##__bytecode)
 102
 103
 104 SCM_STATIC_OBJCODE (cont_objcode) = {
 105   /* This code is the same as in gsubr.c, except we use continuation_call
 106      instead of subr_call. */
 107   OBJCODE_HEADER (8, 19),
 108   /* leave args on the stack */
 109   /* 0 */ scm_op_object_ref, 0, /* push scm_t_contregs smob */
 110   /* 2 */ scm_op_continuation_call, /* and longjmp (whee) */
 111   /* 3 */ scm_op_nop, /* pad to 8 bytes */
 112   /* 4 */ scm_op_nop, scm_op_nop, scm_op_nop, scm_op_nop,
 113   /* 8 */
 114
 115   /* We could put some meta-info to say that this proc is a continuation. Not sure
 116      how to do that, though. */
 117   META_HEADER (19),
 118   /* 0 */ scm_op_make_eol, /* bindings */
 119   /* 1 */ scm_op_make_eol, /* sources */
 120   /* 2 */ scm_op_make_int8, 0, scm_op_make_int8, 3, /* arity: from ip 0 to ip 3 */
 121   /* 6 */ scm_op_make_int8_0, /* the arity is 0 required args */
 122   /* 7 */ scm_op_make_int8_0, /* 0 optionals */
 123   /* 8 */ scm_op_make_true, /* and a rest arg */
 124   /* 9 */ scm_op_list, 0, 5, /* make a list of those 5 vals */
 125   /* 12 */ scm_op_list, 0, 1, /* and the arities will be a list of that one list */
 126   /* 15 */ scm_op_list, 0, 3, /* pack bindings, sources, and arities into list */
 127   /* 18 */ scm_op_return /* and return */
 128   /* 19 */
 129 };
 130
 131
 132 SCM_STATIC_OBJCODE (call_cc_objcode) = {
 133   /* Before Scheme's call/cc is compiled, eval.c will use this hand-coded
 134      call/cc. */
 135   OBJCODE_HEADER (8, 17),
 136   /* 0 */ scm_op_assert_nargs_ee, 0, 1, /* assert that nargs==1 */
 137   /* 3 */ scm_op_local_ref, 0, /* push the proc */
 138   /* 5 */ scm_op_tail_call_cc, /* and call/cc */
 139   /* 6 */ scm_op_nop, scm_op_nop, /* pad to 8 bytes */
 140   /* 8 */
 141
 142   META_HEADER (17),
 143   /* 0 */ scm_op_make_eol, /* bindings */
 144   /* 1 */ scm_op_make_eol, /* sources */
 145   /* 2 */ scm_op_make_int8, 3, scm_op_make_int8, 6, /* arity: from ip 0 to ip 6 */
 146   /* 6 */ scm_op_make_int8_1, /* the arity is 0 required args */
 147   /* 7 */ scm_op_list, 0, 3, /* make a list of those 5 vals */
 148   /* 10 */ scm_op_list, 0, 1, /* and the arities will be a list of that one list */
 149   /* 13 */ scm_op_list, 0, 3, /* pack bindings, sources, and arities into list */
 150   /* 16 */ scm_op_return /* and return */
 151   /* 17 */
 152 };
 153
 154
 155 static SCM
 156 make_continuation_trampoline (SCM contregs)
 157 {
 158   SCM ret = scm_make_program (cont_objcode,
 159                               scm_c_make_vector (1, contregs),
 160                               SCM_BOOL_F);
 161   SCM_SET_CELL_WORD_0 (ret,
 162                        SCM_CELL_WORD_0 (ret) | SCM_F_PROGRAM_IS_CONTINUATION);
 163
 164   return ret;
 165 }
 166
 167
 168 /* {Continuations}
 169  */
 170
 171
 172 static int
 173 continuation_print (SCM obj, SCM port, scm_print_state *state SCM_UNUSED)
 174 {
 175   scm_t_contregs *continuation = SCM_CONTREGS (obj);
 176
 177   scm_puts ("#<continuation ", port);
 178   scm_intprint (continuation->num_stack_items, 10, port);
 179   scm_puts (" @ ", port);
 180   scm_uintprint (SCM_SMOB_DATA_1 (obj), 16, port);
 181   scm_putc ('>', port);
 182   return 1;
 183 }
 184
 185 /* this may return more than once: the first time with the escape
 186    procedure, then subsequently with SCM_UNDEFINED (the vals already having been
 187    placed on the VM stack). */
 188 #define FUNC_NAME "scm_i_make_continuation"
 189 SCM
 190 scm_i_make_continuation (int *first, SCM vm, SCM vm_cont)
 191 {
 192   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 193   SCM cont;
 194   scm_t_contregs *continuation;
 195   long stack_size;
 196   SCM_STACKITEM * src;
 197
 198   SCM_FLUSH_REGISTER_WINDOWS;
 199   stack_size = scm_stack_size (thread->continuation_base);
 200   continuation = scm_gc_malloc (sizeof (scm_t_contregs)
 201                                 + (stack_size - 1) * sizeof (SCM_STACKITEM),
 202                                 "continuation");
 203   continuation->num_stack_items = stack_size;
 204   continuation->dynenv = scm_i_dynwinds ();
 205   continuation->root = thread->continuation_root;
 206   src = thread->continuation_base;
 207 #if ! SCM_STACK_GROWS_UP
 208   src -= stack_size;
 209 #endif
 210   continuation->offset = continuation->stack - src;
 211   memcpy (continuation->stack, src, sizeof (SCM_STACKITEM) * stack_size);
 212   continuation->vm = vm;
 213   continuation->vm_cont = vm_cont;
 214
 215   SCM_NEWSMOB (cont, tc16_continuation, continuation);
 216
 217   *first = !SCM_I_SETJMP (continuation->jmpbuf);
 218   if (*first)
 219     {
 220 #ifdef __ia64__
 221       continuation->backing_store_size =
 222         (char *) scm_ia64_ar_bsp(&continuation->jmpbuf.ctx)
 223         -
 224         (char *) thread->register_backing_store_base;
 225       continuation->backing_store = NULL;
 226       continuation->backing_store =
 227         scm_gc_malloc (continuation->backing_store_size,
 228                        "continuation backing store");
 229       memcpy (continuation->backing_store,
 230               (void *) thread->register_backing_store_base,
 231               continuation->backing_store_size);
 232 #endif /* __ia64__ */
 233       return make_continuation_trampoline (cont);
 234     }
 235   else
 236     return SCM_UNDEFINED;
 237 }
 238 #undef FUNC_NAME
 239
 240 SCM
 241 scm_i_call_with_current_continuation (SCM proc)
 242 {
 243   static SCM call_cc = SCM_BOOL_F;
 244
 245   if (scm_is_false (call_cc))
 246     call_cc = scm_make_program (call_cc_objcode, SCM_BOOL_F, SCM_BOOL_F);
 247
 248   return scm_call_1 (call_cc, proc);
 249 }
 250
 251 SCM
 252 scm_i_continuation_to_frame (SCM continuation)
 253 {
 254   SCM contregs;
 255   scm_t_contregs *cont;
 256
 257   contregs = scm_c_vector_ref (scm_program_objects (continuation), 0);
 258   cont = SCM_CONTREGS (contregs);
 259
 260   if (scm_is_true (cont->vm_cont))
 261     {
 262       struct scm_vm_cont *data = SCM_VM_CONT_DATA (cont->vm_cont);
 263       return scm_c_make_frame (cont->vm_cont,
 264                                data->fp + data->reloc,
 265                                data->sp + data->reloc,
 266                                data->ra,
 267                                data->reloc);
 268     }
 269   else
 270     return SCM_BOOL_F;
 271 }
 272
 273 SCM
 274 scm_i_contregs_vm (SCM contregs)
 275 {
 276   return SCM_CONTREGS (contregs)->vm;
 277 }
 278
 279 SCM
 280 scm_i_contregs_vm_cont (SCM contregs)
 281 {
 282   return SCM_CONTREGS (contregs)->vm_cont;
 283 }
 284
 285
 286 /* {Apply}
 287  */
 288
 289 /* Invoking a continuation proceeds as follows:
 290  *
 291  * - the stack is made large enough for the called continuation
 292  * - the old windchain is unwound down to the branching point
 293  * - the continuation stack is copied into place
 294  * - the windchain is rewound up to the continuation's context
 295  * - the continuation is invoked via longjmp (or setcontext)
 296  *
 297  * This order is important so that unwind and rewind handlers are run
 298  * with their correct stack.
 299  */
 300
 301 static void scm_dynthrow (SCM);
 302
 303 /* Grow the stack by a fixed amount to provide space to copy in the
 304  * continuation.  Possibly this function has to be called several times
 305  * recursively before enough space is available.  Make sure the compiler does
 306  * not optimize the growth array away by storing it's address into a global
 307  * variable.
 308  */
 309
 310 static scm_t_bits scm_i_dummy;
 311
 312 static void
 313 grow_stack (SCM cont)
 314 {
 315   scm_t_bits growth[100];
 316
 317   scm_i_dummy = (scm_t_bits) growth;
 318   scm_dynthrow (cont);
 319 }
 320
 321
 322 /* Copy the continuation stack into the current stack.  Calling functions from
 323  * within this function is safe, since only stack frames below this function's
 324  * own frame are overwritten.  Thus, memcpy can be used for best performance.
 325  */
 326
 327 typedef struct {
 328   scm_t_contregs *continuation;
 329   SCM_STACKITEM *dst;
 330 } copy_stack_data;
 331
 332 static void
 333 copy_stack (void *data)
 334 {
 335   copy_stack_data *d = (copy_stack_data *)data;
 336   memcpy (d->dst, d->continuation->stack,
 337           sizeof (SCM_STACKITEM) * d->continuation->num_stack_items);
 338 #ifdef __ia64__
 339   SCM_I_CURRENT_THREAD->pending_rbs_continuation = d->continuation;
 340 #endif
 341 }
 342
 343 static void
 344 copy_stack_and_call (scm_t_contregs *continuation,
 345                      SCM_STACKITEM * dst)
 346 {
 347   long delta;
 348   copy_stack_data data;
 349
 350   delta = scm_ilength (scm_i_dynwinds ()) - scm_ilength (continuation->dynenv);
 351   data.continuation = continuation;
 352   data.dst = dst;
 353   scm_i_dowinds (continuation->dynenv, delta, copy_stack, &data);
 354
 355   SCM_I_LONGJMP (continuation->jmpbuf, 1);
 356 }
 357
 358 #ifdef __ia64__
 359 void
 360 scm_ia64_longjmp (scm_i_jmp_buf *JB, int VAL)
 361 {
 362   scm_i_thread *t = SCM_I_CURRENT_THREAD;
 363
 364   if (t->pending_rbs_continuation)
 365     {
 366       memcpy (t->register_backing_store_base,
 367               t->pending_rbs_continuation->backing_store,
 368               t->pending_rbs_continuation->backing_store_size);
 369       t->pending_rbs_continuation = NULL;
 370     }
 371   setcontext (&JB->ctx);
 372 }
 373 #endif
 374
 375 /* Call grow_stack until the stack space is large enough, then, as the current
 376  * stack frame might get overwritten, let copy_stack_and_call perform the
 377  * actual copying and continuation calling.
 378  */
 379 static void
 380 scm_dynthrow (SCM cont)
 381 {
 382   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 383   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 384   SCM_STACKITEM *dst = thread->continuation_base;
 385   SCM_STACKITEM stack_top_element;
 386
 387   if (thread->critical_section_level)
 388     {
 389       fprintf (stderr, "continuation invoked from within critical section.\n");
 390       abort ();
 391     }
 392
 393 #if SCM_STACK_GROWS_UP
 394   if (dst + continuation->num_stack_items >= &stack_top_element)
 395     grow_stack (cont);
 396 #else
 397   dst -= continuation->num_stack_items;
 398   if (dst <= &stack_top_element)
 399     grow_stack (cont);
 400 #endif /* def SCM_STACK_GROWS_UP */
 401
 402   SCM_FLUSH_REGISTER_WINDOWS;
 403   copy_stack_and_call (continuation, dst);
 404 }
 405
 406
 407 void
 408 scm_i_check_continuation (SCM cont)
 409 {
 410   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 411   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 412
 413   if (!scm_is_eq (continuation->root, thread->continuation_root))
 414     scm_misc_error
 415       ("%continuation-call",
 416        "invoking continuation would cross continuation barrier: ~A",
 417        scm_list_1 (cont));
 418 }
 419
 420 void
 421 scm_i_reinstate_continuation (SCM cont)
 422 {
 423   scm_dynthrow (cont);
 424 }
 425
 426 SCM
 427 scm_i_with_continuation_barrier (scm_t_catch_body body,
 428                                  void *body_data,
 429                                  scm_t_catch_handler handler,
 430                                  void *handler_data,
 431                                  scm_t_catch_handler pre_unwind_handler,
 432                                  void *pre_unwind_handler_data)
 433 {
 434   SCM_STACKITEM stack_item;
 435   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 436   SCM old_controot;
 437   SCM_STACKITEM *old_contbase;
 438   SCM result;
 439
 440   /* Establish a fresh continuation root.
 441    */
 442   old_controot = thread->continuation_root;
 443   old_contbase = thread->continuation_base;
 444   thread->continuation_root = scm_cons (thread->handle, old_controot);
 445   thread->continuation_base = &stack_item;
 446
 447   /* Call FUNC inside a catch all.  This is now guaranteed to return
 448      directly and exactly once.
 449   */
 450   result = scm_c_catch (SCM_BOOL_T,
 451                         body, body_data,
 452                         handler, handler_data,
 453                         pre_unwind_handler, pre_unwind_handler_data);
 454
 455   /* Return to old continuation root.
 456    */
 457   thread->continuation_base = old_contbase;
 458   thread->continuation_root = old_controot;
 459
 460   return result;
 461 }
 462
 463 \f
 464
 465 static int
 466 should_print_backtrace (SCM tag, SCM stack)
 467 {
 468   return SCM_BACKTRACE_P
 469     && scm_is_true (stack)
 470     && scm_initialized_p
 471     /* It's generally not useful to print backtraces for errors reading
 472        or expanding code in these fallback catch statements. */
 473     && !scm_is_eq (tag, scm_from_latin1_symbol ("read-error"))
 474     && !scm_is_eq (tag, scm_from_latin1_symbol ("syntax-error"));
 475 }
 476
 477 static void
 478 print_exception_and_backtrace (SCM port, SCM tag, SCM args)
 479 {
 480   SCM stack, frame;
 481
 482   /* We get here via a throw to a catch-all.  In that case there is the
 483      throw frame active, and this catch closure, so narrow by two
 484      frames.  */
 485   stack = scm_make_stack (SCM_BOOL_T, scm_list_1 (scm_from_int (2)));
 486   frame = scm_is_true (stack) ? scm_stack_ref (stack, SCM_INUM0) : SCM_BOOL_F;
 487
 488   if (should_print_backtrace (tag, stack))
 489     {
 490       scm_puts ("Backtrace:\n", port);
 491       scm_display_backtrace_with_highlights (stack, port,
 492                                              SCM_BOOL_F, SCM_BOOL_F,
 493                                              SCM_EOL);
 494       scm_newline (port);
 495     }
 496
 497   scm_print_exception (port, frame, tag, args);
 498 }
 499
 500 \f
 501
 502 struct c_data {
 503   void *(*func) (void *);
 504   void *data;
 505   void *result;
 506 };
 507
 508 static SCM
 509 c_body (void *d)
 510 {
 511   struct c_data *data = (struct c_data *)d;
 512   data->result = data->func (data->data);
 513   return SCM_UNSPECIFIED;
 514 }
 515
 516 static SCM
 517 c_handler (void *d, SCM tag, SCM args)
 518 {
 519   struct c_data *data;
 520
 521   /* If TAG is `quit', exit() the process.  */
 522   if (scm_is_eq (tag, scm_from_latin1_symbol ("quit")))
 523     exit (scm_exit_status (args));
 524
 525   data = (struct c_data *)d;
 526   data->result = NULL;
 527   return SCM_UNSPECIFIED;
 528 }
 529
 530 static SCM
 531 pre_unwind_handler (void *error_port, SCM tag, SCM args)
 532 {
 533   /* Print the exception unless TAG is  `quit'.  */
 534   if (!scm_is_eq (tag, scm_from_latin1_symbol ("quit")))
 535     print_exception_and_backtrace (PTR2SCM (error_port), tag, args);
 536
 537   return SCM_UNSPECIFIED;
 538 }
 539
 540 void *
 541 scm_c_with_continuation_barrier (void *(*func) (void *), void *data)
 542 {
 543   struct c_data c_data;
 544   c_data.func = func;
 545   c_data.data = data;
 546   scm_i_with_continuation_barrier (c_body, &c_data,
 547                                    c_handler, &c_data,
 548                                    pre_unwind_handler,
 549                                    SCM2PTR (scm_current_error_port ()));
 550   return c_data.result;
 551 }
 552
 553 struct scm_data {
 554   SCM proc;
 555 };
 556
 557 static SCM
 558 scm_body (void *d)
 559 {
 560   struct scm_data *data = (struct scm_data *)d;
 561   return scm_call_0 (data->proc);
 562 }
 563
 564 static SCM
 565 scm_handler (void *d, SCM tag, SCM args)
 566 {
 567   /* Print a message.  Note that if TAG is `quit', this will exit() the
 568      process.  */
 569   scm_handle_by_message_noexit (NULL, tag, args);
 570
 571   return SCM_BOOL_F;
 572 }
 573
 574 SCM_DEFINE (scm_with_continuation_barrier, "with-continuation-barrier", 1,0,0,
 575             (SCM proc),
 576 "Call @var{proc} and return its result.  Do not allow the invocation of\n"
 577 "continuations that would leave or enter the dynamic extent of the call\n"
 578 "to @code{with-continuation-barrier}.  Such an attempt causes an error\n"
 579 "to be signaled.\n"
 580 "\n"
 581 "Throws (such as errors) that are not caught from within @var{proc} are\n"
 582 "caught by @code{with-continuation-barrier}.  In that case, a short\n"
 583 "message is printed to the current error port and @code{#f} is returned.\n"
 584 "\n"
 585 "Thus, @code{with-continuation-barrier} returns exactly once.\n")
 586 #define FUNC_NAME s_scm_with_continuation_barrier
 587 {
 588   struct scm_data scm_data;
 589   scm_data.proc = proc;
 590   return scm_i_with_continuation_barrier (scm_body, &scm_data,
 591                                           scm_handler, &scm_data,
 592                                           pre_unwind_handler,
 593                                           SCM2PTR (scm_current_error_port ()));
 594 }
 595 #undef FUNC_NAME
 596
 597 void
 598 scm_init_continuations ()
 599 {
 600   tc16_continuation = scm_make_smob_type ("continuation", 0);
 601   scm_set_smob_print (tc16_continuation, continuation_print);
 602 #include "libguile/continuations.x"
 603 }
 604
 605 /*
 606   Local Variables:
 607   c-file-style: "gnu"
 608   End:
 609 */