libguile/continuations.c

   1 /* Copyright (C) 1995,1996,1998,2000,2001,2004, 2006, 2008, 2009, 2010 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 (sizeof(sym##__unaligned) + alignment - 1); \
  86                sym = ALIGN_PTR (type, sym, alignment);                  \
  87                memcpy (sym, sym##__unaligned, sizeof(sym##__unaligned));) \
  88 static type *sym = NULL;                                                \
  89 static const type sym##__unaligned[]
  90 #endif
  91
  92 #define STATIC_OBJCODE_TAG                                      \
  93   SCM_PACK (scm_tc7_objcode | (SCM_F_OBJCODE_IS_STATIC << 8))
  94
  95 #define SCM_STATIC_OBJCODE(sym)                                         \
  96   SCM_DECLARE_STATIC_ALIGNED_ARRAY (scm_t_uint8, sym##__bytecode);      \
  97   SCM_STATIC_ALIGNED_ARRAY (8, scm_t_cell, sym##__cells) = {            \
  98     { STATIC_OBJCODE_TAG, SCM_PACK (sym##__bytecode) },                 \
  99     { SCM_BOOL_F, SCM_PACK (0) }                                        \
 100   };                                                                    \
 101   static const SCM sym = SCM_PACK (sym##__cells);                       \
 102   SCM_STATIC_ALIGNED_ARRAY (8, scm_t_uint8, sym##__bytecode)
 103
 104
 105 SCM_STATIC_OBJCODE (cont_objcode) = {
 106   /* This code is the same as in gsubr.c, except we use continuation_call
 107      instead of subr_call. */
 108   OBJCODE_HEADER (8, 19),
 109   /* leave args on the stack */
 110   /* 0 */ scm_op_object_ref, 0, /* push scm_t_contregs smob */
 111   /* 2 */ scm_op_continuation_call, /* and longjmp (whee) */
 112   /* 3 */ scm_op_nop, /* pad to 8 bytes */
 113   /* 4 */ scm_op_nop, scm_op_nop, scm_op_nop, scm_op_nop,
 114   /* 8 */
 115
 116   /* We could put some meta-info to say that this proc is a continuation. Not sure
 117      how to do that, though. */
 118   META_HEADER (19),
 119   /* 0 */ scm_op_make_eol, /* bindings */
 120   /* 1 */ scm_op_make_eol, /* sources */
 121   /* 2 */ scm_op_make_int8, 0, scm_op_make_int8, 3, /* arity: from ip 0 to ip 3 */
 122   /* 6 */ scm_op_make_int8_0, /* the arity is 0 required args */
 123   /* 7 */ scm_op_make_int8_0, /* 0 optionals */
 124   /* 8 */ scm_op_make_true, /* and a rest arg */
 125   /* 9 */ scm_op_list, 0, 5, /* make a list of those 5 vals */
 126   /* 12 */ scm_op_list, 0, 1, /* and the arities will be a list of that one list */
 127   /* 15 */ scm_op_list, 0, 3, /* pack bindings, sources, and arities into list */
 128   /* 18 */ scm_op_return /* and return */
 129   /* 19 */
 130 };
 131
 132
 133 SCM_STATIC_OBJCODE (call_cc_objcode) = {
 134   /* Before Scheme's call/cc is compiled, eval.c will use this hand-coded
 135      call/cc. */
 136   OBJCODE_HEADER (8, 17),
 137   /* 0 */ scm_op_assert_nargs_ee, 0, 1, /* assert that nargs==1 */
 138   /* 3 */ scm_op_local_ref, 0, /* push the proc */
 139   /* 5 */ scm_op_tail_call_cc, /* and call/cc */
 140   /* 6 */ scm_op_nop, scm_op_nop, /* pad to 8 bytes */
 141   /* 8 */
 142
 143   META_HEADER (17),
 144   /* 0 */ scm_op_make_eol, /* bindings */
 145   /* 1 */ scm_op_make_eol, /* sources */
 146   /* 2 */ scm_op_make_int8, 3, scm_op_make_int8, 6, /* arity: from ip 0 to ip 6 */
 147   /* 6 */ scm_op_make_int8_1, /* the arity is 0 required args */
 148   /* 7 */ scm_op_list, 0, 3, /* make a list of those 5 vals */
 149   /* 10 */ scm_op_list, 0, 1, /* and the arities will be a list of that one list */
 150   /* 13 */ scm_op_list, 0, 3, /* pack bindings, sources, and arities into list */
 151   /* 16 */ scm_op_return /* and return */
 152   /* 17 */
 153 };
 154
 155
 156 static SCM
 157 make_continuation_trampoline (SCM contregs)
 158 {
 159   SCM ret = scm_make_program (cont_objcode,
 160                               scm_c_make_vector (1, contregs),
 161                               SCM_BOOL_F);
 162   SCM_SET_CELL_WORD_0 (ret,
 163                        SCM_CELL_WORD_0 (ret) | SCM_F_PROGRAM_IS_CONTINUATION);
 164
 165   return ret;
 166 }
 167
 168
 169 /* {Continuations}
 170  */
 171
 172
 173 static int
 174 continuation_print (SCM obj, SCM port, scm_print_state *state SCM_UNUSED)
 175 {
 176   scm_t_contregs *continuation = SCM_CONTREGS (obj);
 177
 178   scm_puts ("#<continuation ", port);
 179   scm_intprint (continuation->num_stack_items, 10, port);
 180   scm_puts (" @ ", port);
 181   scm_uintprint (SCM_SMOB_DATA_1 (obj), 16, port);
 182   scm_putc ('>', port);
 183   return 1;
 184 }
 185
 186 /* this may return more than once: the first time with the escape
 187    procedure, then subsequently with SCM_UNDEFINED (the vals already having been
 188    placed on the VM stack). */
 189 #define FUNC_NAME "scm_i_make_continuation"
 190 SCM
 191 scm_i_make_continuation (int *first, SCM vm, SCM vm_cont)
 192 {
 193   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 194   SCM cont;
 195   scm_t_contregs *continuation;
 196   long stack_size;
 197   SCM_STACKITEM * src;
 198
 199   SCM_FLUSH_REGISTER_WINDOWS;
 200   stack_size = scm_stack_size (thread->continuation_base);
 201   continuation = scm_gc_malloc (sizeof (scm_t_contregs)
 202                                 + (stack_size - 1) * sizeof (SCM_STACKITEM),
 203                                 "continuation");
 204   continuation->num_stack_items = stack_size;
 205   continuation->dynenv = scm_i_dynwinds ();
 206   continuation->root = thread->continuation_root;
 207   src = thread->continuation_base;
 208 #if ! SCM_STACK_GROWS_UP
 209   src -= stack_size;
 210 #endif
 211   continuation->offset = continuation->stack - src;
 212   memcpy (continuation->stack, src, sizeof (SCM_STACKITEM) * stack_size);
 213   continuation->vm = vm;
 214   continuation->vm_cont = vm_cont;
 215
 216   SCM_NEWSMOB (cont, tc16_continuation, continuation);
 217
 218   *first = !SCM_I_SETJMP (continuation->jmpbuf);
 219   if (*first)
 220     {
 221 #ifdef __ia64__
 222       continuation->backing_store_size =
 223         (char *) scm_ia64_ar_bsp(&continuation->jmpbuf.ctx)
 224         -
 225         (char *) thread->register_backing_store_base;
 226       continuation->backing_store = NULL;
 227       continuation->backing_store =
 228         scm_gc_malloc (continuation->backing_store_size,
 229                        "continuation backing store");
 230       memcpy (continuation->backing_store,
 231               (void *) thread->register_backing_store_base,
 232               continuation->backing_store_size);
 233 #endif /* __ia64__ */
 234       return make_continuation_trampoline (cont);
 235     }
 236   else
 237     return SCM_UNDEFINED;
 238 }
 239 #undef FUNC_NAME
 240
 241 SCM
 242 scm_i_call_with_current_continuation (SCM proc)
 243 {
 244   static SCM call_cc = SCM_BOOL_F;
 245
 246   if (scm_is_false (call_cc))
 247     call_cc = scm_make_program (call_cc_objcode, SCM_BOOL_F, SCM_BOOL_F);
 248
 249   return scm_call_1 (call_cc, proc);
 250 }
 251
 252 SCM
 253 scm_i_continuation_to_frame (SCM continuation)
 254 {
 255   SCM contregs;
 256   scm_t_contregs *cont;
 257
 258   contregs = scm_c_vector_ref (scm_program_objects (continuation), 0);
 259   cont = SCM_CONTREGS (contregs);
 260
 261   if (scm_is_true (cont->vm_cont))
 262     {
 263       struct scm_vm_cont *data = SCM_VM_CONT_DATA (cont->vm_cont);
 264       return scm_c_make_frame (cont->vm_cont,
 265                                data->fp + data->reloc,
 266                                data->sp + data->reloc,
 267                                data->ra,
 268                                data->reloc);
 269     }
 270   else
 271     return SCM_BOOL_F;
 272 }
 273
 274 SCM
 275 scm_i_contregs_vm (SCM contregs)
 276 {
 277   return SCM_CONTREGS (contregs)->vm;
 278 }
 279
 280 SCM
 281 scm_i_contregs_vm_cont (SCM contregs)
 282 {
 283   return SCM_CONTREGS (contregs)->vm_cont;
 284 }
 285
 286
 287 /* {Apply}
 288  */
 289
 290 /* Invoking a continuation proceeds as follows:
 291  *
 292  * - the stack is made large enough for the called continuation
 293  * - the old windchain is unwound down to the branching point
 294  * - the continuation stack is copied into place
 295  * - the windchain is rewound up to the continuation's context
 296  * - the continuation is invoked via longjmp (or setcontext)
 297  *
 298  * This order is important so that unwind and rewind handlers are run
 299  * with their correct stack.
 300  */
 301
 302 static void scm_dynthrow (SCM);
 303
 304 /* Grow the stack by a fixed amount to provide space to copy in the
 305  * continuation.  Possibly this function has to be called several times
 306  * recursively before enough space is available.  Make sure the compiler does
 307  * not optimize the growth array away by storing it's address into a global
 308  * variable.
 309  */
 310
 311 static scm_t_bits scm_i_dummy;
 312
 313 static void
 314 grow_stack (SCM cont)
 315 {
 316   scm_t_bits growth[100];
 317
 318   scm_i_dummy = (scm_t_bits) growth;
 319   scm_dynthrow (cont);
 320 }
 321
 322
 323 /* Copy the continuation stack into the current stack.  Calling functions from
 324  * within this function is safe, since only stack frames below this function's
 325  * own frame are overwritten.  Thus, memcpy can be used for best performance.
 326  */
 327
 328 typedef struct {
 329   scm_t_contregs *continuation;
 330   SCM_STACKITEM *dst;
 331 } copy_stack_data;
 332
 333 static void
 334 copy_stack (void *data)
 335 {
 336   copy_stack_data *d = (copy_stack_data *)data;
 337   memcpy (d->dst, d->continuation->stack,
 338           sizeof (SCM_STACKITEM) * d->continuation->num_stack_items);
 339 #ifdef __ia64__
 340   SCM_I_CURRENT_THREAD->pending_rbs_continuation = d->continuation;
 341 #endif
 342 }
 343
 344 static void
 345 copy_stack_and_call (scm_t_contregs *continuation,
 346                      SCM_STACKITEM * dst)
 347 {
 348   long delta;
 349   copy_stack_data data;
 350
 351   delta = scm_ilength (scm_i_dynwinds ()) - scm_ilength (continuation->dynenv);
 352   data.continuation = continuation;
 353   data.dst = dst;
 354   scm_i_dowinds (continuation->dynenv, delta, copy_stack, &data);
 355
 356   SCM_I_LONGJMP (continuation->jmpbuf, 1);
 357 }
 358
 359 #ifdef __ia64__
 360 void
 361 scm_ia64_longjmp (scm_i_jmp_buf *JB, int VAL)
 362 {
 363   scm_i_thread *t = SCM_I_CURRENT_THREAD;
 364
 365   if (t->pending_rbs_continuation)
 366     {
 367       memcpy (t->register_backing_store_base,
 368               t->pending_rbs_continuation->backing_store,
 369               t->pending_rbs_continuation->backing_store_size);
 370       t->pending_rbs_continuation = NULL;
 371     }
 372   setcontext (&JB->ctx);
 373 }
 374 #endif
 375
 376 /* Call grow_stack until the stack space is large enough, then, as the current
 377  * stack frame might get overwritten, let copy_stack_and_call perform the
 378  * actual copying and continuation calling.
 379  */
 380 static void
 381 scm_dynthrow (SCM cont)
 382 {
 383   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 384   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 385   SCM_STACKITEM *dst = thread->continuation_base;
 386   SCM_STACKITEM stack_top_element;
 387
 388   if (thread->critical_section_level)
 389     {
 390       fprintf (stderr, "continuation invoked from within critical section.\n");
 391       abort ();
 392     }
 393
 394 #if SCM_STACK_GROWS_UP
 395   if (dst + continuation->num_stack_items >= &stack_top_element)
 396     grow_stack (cont);
 397 #else
 398   dst -= continuation->num_stack_items;
 399   if (dst <= &stack_top_element)
 400     grow_stack (cont);
 401 #endif /* def SCM_STACK_GROWS_UP */
 402
 403   SCM_FLUSH_REGISTER_WINDOWS;
 404   copy_stack_and_call (continuation, dst);
 405 }
 406
 407
 408 void
 409 scm_i_check_continuation (SCM cont)
 410 {
 411   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 412   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 413
 414   if (continuation->root != thread->continuation_root)
 415     scm_misc_error
 416       ("%continuation-call",
 417        "invoking continuation would cross continuation barrier: ~A",
 418        scm_list_1 (cont));
 419 }
 420
 421 void
 422 scm_i_reinstate_continuation (SCM cont)
 423 {
 424   scm_dynthrow (cont);
 425 }
 426
 427 SCM
 428 scm_i_with_continuation_barrier (scm_t_catch_body body,
 429                                  void *body_data,
 430                                  scm_t_catch_handler handler,
 431                                  void *handler_data,
 432                                  scm_t_catch_handler pre_unwind_handler,
 433                                  void *pre_unwind_handler_data)
 434 {
 435   SCM_STACKITEM stack_item;
 436   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 437   SCM old_controot;
 438   SCM_STACKITEM *old_contbase;
 439   SCM result;
 440
 441   /* Establish a fresh continuation root.
 442    */
 443   old_controot = thread->continuation_root;
 444   old_contbase = thread->continuation_base;
 445   thread->continuation_root = scm_cons (thread->handle, old_controot);
 446   thread->continuation_base = &stack_item;
 447
 448   /* Call FUNC inside a catch all.  This is now guaranteed to return
 449      directly and exactly once.
 450   */
 451   result = scm_c_catch (SCM_BOOL_T,
 452                         body, body_data,
 453                         handler, handler_data,
 454                         pre_unwind_handler, pre_unwind_handler_data);
 455
 456   /* Return to old continuation root.
 457    */
 458   thread->continuation_base = old_contbase;
 459   thread->continuation_root = old_controot;
 460
 461   return result;
 462 }
 463
 464 struct c_data {
 465   void *(*func) (void *);
 466   void *data;
 467   void *result;
 468 };
 469
 470 static SCM
 471 c_body (void *d)
 472 {
 473   struct c_data *data = (struct c_data *)d;
 474   data->result = data->func (data->data);
 475   return SCM_UNSPECIFIED;
 476 }
 477
 478 static SCM
 479 c_handler (void *d, SCM tag, SCM args)
 480 {
 481   struct c_data *data = (struct c_data *)d;
 482   data->result = NULL;
 483   return SCM_UNSPECIFIED;
 484 }
 485
 486 void *
 487 scm_c_with_continuation_barrier (void *(*func) (void *), void *data)
 488 {
 489   struct c_data c_data;
 490   c_data.func = func;
 491   c_data.data = data;
 492   scm_i_with_continuation_barrier (c_body, &c_data,
 493                                    c_handler, &c_data,
 494                                    scm_handle_by_message_noexit, NULL);
 495   return c_data.result;
 496 }
 497
 498 struct scm_data {
 499   SCM proc;
 500 };
 501
 502 static SCM
 503 scm_body (void *d)
 504 {
 505   struct scm_data *data = (struct scm_data *)d;
 506   return scm_call_0 (data->proc);
 507 }
 508
 509 static SCM
 510 scm_handler (void *d, SCM tag, SCM args)
 511 {
 512   return SCM_BOOL_F;
 513 }
 514
 515 SCM_DEFINE (scm_with_continuation_barrier, "with-continuation-barrier", 1,0,0,
 516             (SCM proc),
 517 "Call @var{proc} and return its result.  Do not allow the invocation of\n"
 518 "continuations that would leave or enter the dynamic extent of the call\n"
 519 "to @code{with-continuation-barrier}.  Such an attempt causes an error\n"
 520 "to be signaled.\n"
 521 "\n"
 522 "Throws (such as errors) that are not caught from within @var{proc} are\n"
 523 "caught by @code{with-continuation-barrier}.  In that case, a short\n"
 524 "message is printed to the current error port and @code{#f} is returned.\n"
 525 "\n"
 526 "Thus, @code{with-continuation-barrier} returns exactly once.\n")
 527 #define FUNC_NAME s_scm_with_continuation_barrier
 528 {
 529   struct scm_data scm_data;
 530   scm_data.proc = proc;
 531   return scm_i_with_continuation_barrier (scm_body, &scm_data,
 532                                           scm_handler, &scm_data,
 533                                           scm_handle_by_message_noexit, NULL);
 534 }
 535 #undef FUNC_NAME
 536
 537 void
 538 scm_init_continuations ()
 539 {
 540   tc16_continuation = scm_make_smob_type ("continuation", 0);
 541   scm_set_smob_print (tc16_continuation, continuation_print);
 542 #include "libguile/continuations.x"
 543 }
 544
 545 /*
 546   Local Variables:
 547   c-file-style: "gnu"
 548   End:
 549 */