libguile/continuations.c

   1 /* Copyright (C) 1995,1996,1998,2000,2001,2004, 2006, 2008, 2009, 2010, 2011, 2012, 2013 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 <assert.h>
  28 #include <string.h>
  29 #include <stdio.h>
  30
  31 #include "libguile/async.h"
  32 #include "libguile/debug.h"
  33 #include "libguile/root.h"
  34 #include "libguile/stackchk.h"
  35 #include "libguile/smob.h"
  36 #include "libguile/ports.h"
  37 #include "libguile/dynstack.h"
  38 #include "libguile/eval.h"
  39 #include "libguile/vm.h"
  40 #include "libguile/instructions.h"
  41
  42 #include "libguile/validate.h"
  43 #include "libguile/continuations.h"
  44
  45 \f
  46
  47 static scm_t_bits tc16_continuation;
  48 #define SCM_CONTREGSP(x)        SCM_TYP16_PREDICATE (tc16_continuation, x)
  49
  50 #define SCM_CONTREGS(x)         ((scm_t_contregs *) SCM_SMOB_DATA_1 (x))
  51
  52 #define SCM_CONTINUATION_LENGTH(x) (SCM_CONTREGS (x)->num_stack_items)
  53 #define SCM_SET_CONTINUATION_LENGTH(x, n)\
  54    (SCM_CONTREGS (x)->num_stack_items = (n))
  55 #define SCM_JMPBUF(x)            ((SCM_CONTREGS (x))->jmpbuf)
  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 code will
  62    reinstate the continuation. Here, as in gsubr.c, we define the form
  63    of that trampoline function.
  64  */
  65
  66 static const scm_t_uint32 continuation_stub_code[] =
  67   {
  68     SCM_PACK_OP_24 (continuation_call, 0)
  69   };
  70
  71 static SCM
  72 make_continuation_trampoline (SCM contregs)
  73 {
  74   SCM ret;
  75   scm_t_bits nfree = 1;
  76   scm_t_bits flags = SCM_F_PROGRAM_IS_CONTINUATION;
  77
  78   ret = scm_words (scm_tc7_program | (nfree << 16) | flags, nfree + 2);
  79   SCM_SET_CELL_WORD_1 (ret, continuation_stub_code);
  80   SCM_PROGRAM_FREE_VARIABLE_SET (ret, 0, contregs);
  81
  82   return ret;
  83 }
  84
  85
  86 /* {Continuations}
  87  */
  88
  89
  90 static int
  91 continuation_print (SCM obj, SCM port, scm_print_state *state SCM_UNUSED)
  92 {
  93   scm_t_contregs *continuation = SCM_CONTREGS (obj);
  94
  95   scm_puts_unlocked ("#<continuation ", port);
  96   scm_intprint (continuation->num_stack_items, 10, port);
  97   scm_puts_unlocked (" @ ", port);
  98   scm_uintprint (SCM_SMOB_DATA_1 (obj), 16, port);
  99   scm_putc_unlocked ('>', port);
 100   return 1;
 101 }
 102
 103 /* James Clark came up with this neat one instruction fix for
 104  * continuations on the SPARC.  It flushes the register windows so
 105  * that all the state of the process is contained in the stack.
 106  */
 107
 108 #if defined (sparc) || defined (__sparc__) || defined (__sparc)
 109 # define SCM_FLUSH_REGISTER_WINDOWS asm("ta 3")
 110 #else
 111 # define SCM_FLUSH_REGISTER_WINDOWS /* empty */
 112 #endif
 113
 114 /* this may return more than once: the first time with the escape
 115    procedure, then subsequently with SCM_UNDEFINED (the vals already having been
 116    placed on the VM stack). */
 117 #define FUNC_NAME "scm_i_make_continuation"
 118 SCM
 119 scm_i_make_continuation (int *first, SCM vm, SCM vm_cont)
 120 {
 121   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 122   SCM cont;
 123   scm_t_contregs *continuation;
 124   long stack_size;
 125   SCM_STACKITEM * src;
 126
 127   SCM_FLUSH_REGISTER_WINDOWS;
 128   stack_size = scm_stack_size (thread->continuation_base);
 129   continuation = scm_gc_malloc (sizeof (scm_t_contregs)
 130                                 + (stack_size - 1) * sizeof (SCM_STACKITEM),
 131                                 "continuation");
 132   continuation->num_stack_items = stack_size;
 133   continuation->root = thread->continuation_root;
 134   src = thread->continuation_base;
 135 #if ! SCM_STACK_GROWS_UP
 136   src -= stack_size;
 137 #endif
 138   continuation->offset = continuation->stack - src;
 139   memcpy (continuation->stack, src, sizeof (SCM_STACKITEM) * stack_size);
 140   continuation->vm = vm;
 141   continuation->vm_cont = vm_cont;
 142
 143   SCM_NEWSMOB (cont, tc16_continuation, continuation);
 144
 145   *first = !SCM_I_SETJMP (continuation->jmpbuf);
 146   if (*first)
 147     {
 148 #ifdef __ia64__
 149       continuation->backing_store_size =
 150         (char *) scm_ia64_ar_bsp(&continuation->jmpbuf.ctx)
 151         -
 152         (char *) thread->register_backing_store_base;
 153       continuation->backing_store = NULL;
 154       continuation->backing_store =
 155         scm_gc_malloc (continuation->backing_store_size,
 156                        "continuation backing store");
 157       memcpy (continuation->backing_store,
 158               (void *) thread->register_backing_store_base,
 159               continuation->backing_store_size);
 160 #endif /* __ia64__ */
 161       return make_continuation_trampoline (cont);
 162     }
 163   else
 164     return SCM_UNDEFINED;
 165 }
 166 #undef FUNC_NAME
 167
 168 SCM
 169 scm_i_continuation_to_frame (SCM continuation)
 170 {
 171   SCM contregs;
 172   scm_t_contregs *cont;
 173
 174   contregs = SCM_PROGRAM_FREE_VARIABLE_REF (continuation, 0);
 175   cont = SCM_CONTREGS (contregs);
 176
 177   if (scm_is_true (cont->vm_cont))
 178     {
 179       struct scm_vm_cont *data = SCM_VM_CONT_DATA (cont->vm_cont);
 180       return scm_c_make_frame (cont->vm_cont,
 181                                data->fp + data->reloc,
 182                                data->sp + data->reloc,
 183                                data->ra,
 184                                data->reloc);
 185     }
 186   else
 187     return SCM_BOOL_F;
 188 }
 189
 190 SCM
 191 scm_i_contregs_vm (SCM contregs)
 192 {
 193   return SCM_CONTREGS (contregs)->vm;
 194 }
 195
 196 SCM
 197 scm_i_contregs_vm_cont (SCM contregs)
 198 {
 199   return SCM_CONTREGS (contregs)->vm_cont;
 200 }
 201
 202
 203 /* {Apply}
 204  */
 205
 206 /* Invoking a continuation proceeds as follows:
 207  *
 208  * - the stack is made large enough for the called continuation
 209  * - the old windchain is unwound down to the branching point
 210  * - the continuation stack is copied into place
 211  * - the windchain is rewound up to the continuation's context
 212  * - the continuation is invoked via longjmp (or setcontext)
 213  *
 214  * This order is important so that unwind and rewind handlers are run
 215  * with their correct stack.
 216  */
 217
 218 static void scm_dynthrow (SCM);
 219
 220 /* Grow the stack by a fixed amount to provide space to copy in the
 221  * continuation.  Possibly this function has to be called several times
 222  * recursively before enough space is available.  Make sure the compiler does
 223  * not optimize the growth array away by storing it's address into a global
 224  * variable.
 225  */
 226
 227 static scm_t_bits scm_i_dummy;
 228
 229 static void
 230 grow_stack (SCM cont)
 231 {
 232   scm_t_bits growth[100];
 233
 234   scm_i_dummy = (scm_t_bits) growth;
 235   scm_dynthrow (cont);
 236 }
 237
 238
 239 /* Copy the continuation stack into the current stack.  Calling functions from
 240  * within this function is safe, since only stack frames below this function's
 241  * own frame are overwritten.  Thus, memcpy can be used for best performance.
 242  */
 243
 244 static void
 245 copy_stack_and_call (scm_t_contregs *continuation,
 246                      SCM_STACKITEM * dst)
 247 {
 248   scm_t_dynstack *dynstack;
 249   scm_t_bits *joint;
 250   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 251
 252   dynstack = SCM_VM_CONT_DATA (continuation->vm_cont)->dynstack;
 253
 254   joint = scm_dynstack_unwind_fork (&thread->dynstack, dynstack);
 255
 256   memcpy (dst, continuation->stack,
 257           sizeof (SCM_STACKITEM) * continuation->num_stack_items);
 258 #ifdef __ia64__
 259   thread->pending_rbs_continuation = continuation;
 260 #endif
 261
 262   scm_dynstack_wind (&thread->dynstack, joint);
 263
 264   SCM_I_LONGJMP (continuation->jmpbuf, 1);
 265 }
 266
 267 #ifdef __ia64__
 268 void
 269 scm_ia64_longjmp (scm_i_jmp_buf *JB, int VAL)
 270 {
 271   scm_i_thread *t = SCM_I_CURRENT_THREAD;
 272
 273   if (t->pending_rbs_continuation)
 274     {
 275       memcpy (t->register_backing_store_base,
 276               t->pending_rbs_continuation->backing_store,
 277               t->pending_rbs_continuation->backing_store_size);
 278       t->pending_rbs_continuation = NULL;
 279     }
 280   setcontext (&JB->ctx);
 281 }
 282 #endif
 283
 284 /* Call grow_stack until the stack space is large enough, then, as the current
 285  * stack frame might get overwritten, let copy_stack_and_call perform the
 286  * actual copying and continuation calling.
 287  */
 288 static void
 289 scm_dynthrow (SCM cont)
 290 {
 291   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 292   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 293   SCM_STACKITEM *dst = thread->continuation_base;
 294   SCM_STACKITEM stack_top_element;
 295
 296   if (thread->critical_section_level)
 297     {
 298       fprintf (stderr, "continuation invoked from within critical section.\n");
 299       abort ();
 300     }
 301
 302 #if SCM_STACK_GROWS_UP
 303   if (dst + continuation->num_stack_items >= &stack_top_element)
 304     grow_stack (cont);
 305 #else
 306   dst -= continuation->num_stack_items;
 307   if (dst <= &stack_top_element)
 308     grow_stack (cont);
 309 #endif /* def SCM_STACK_GROWS_UP */
 310
 311   SCM_FLUSH_REGISTER_WINDOWS;
 312   copy_stack_and_call (continuation, dst);
 313 }
 314
 315
 316 void
 317 scm_i_check_continuation (SCM cont)
 318 {
 319   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 320   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 321
 322   if (!scm_is_eq (continuation->root, thread->continuation_root))
 323     scm_misc_error
 324       ("%continuation-call",
 325        "invoking continuation would cross continuation barrier: ~A",
 326        scm_list_1 (cont));
 327 }
 328
 329 void
 330 scm_i_reinstate_continuation (SCM cont)
 331 {
 332   scm_dynthrow (cont);
 333 }
 334
 335 SCM
 336 scm_i_with_continuation_barrier (scm_t_catch_body body,
 337                                  void *body_data,
 338                                  scm_t_catch_handler handler,
 339                                  void *handler_data,
 340                                  scm_t_catch_handler pre_unwind_handler,
 341                                  void *pre_unwind_handler_data)
 342 {
 343   SCM_STACKITEM stack_item;
 344   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 345   SCM old_controot;
 346   SCM_STACKITEM *old_contbase;
 347   SCM result;
 348
 349   /* Establish a fresh continuation root.
 350    */
 351   old_controot = thread->continuation_root;
 352   old_contbase = thread->continuation_base;
 353   thread->continuation_root = scm_cons (thread->handle, old_controot);
 354   thread->continuation_base = &stack_item;
 355
 356   /* Call FUNC inside a catch all.  This is now guaranteed to return
 357      directly and exactly once.
 358   */
 359   result = scm_c_catch (SCM_BOOL_T,
 360                         body, body_data,
 361                         handler, handler_data,
 362                         pre_unwind_handler, pre_unwind_handler_data);
 363
 364   /* Return to old continuation root.
 365    */
 366   thread->continuation_base = old_contbase;
 367   thread->continuation_root = old_controot;
 368
 369   return result;
 370 }
 371
 372 \f
 373
 374 static int
 375 should_print_backtrace (SCM tag, SCM stack)
 376 {
 377   return SCM_BACKTRACE_P
 378     && scm_is_true (stack)
 379     && scm_initialized_p
 380     /* It's generally not useful to print backtraces for errors reading
 381        or expanding code in these fallback catch statements. */
 382     && !scm_is_eq (tag, scm_from_latin1_symbol ("read-error"))
 383     && !scm_is_eq (tag, scm_from_latin1_symbol ("syntax-error"));
 384 }
 385
 386 static void
 387 print_exception_and_backtrace (SCM port, SCM tag, SCM args)
 388 {
 389   SCM stack, frame;
 390
 391   /* We get here via a throw to a catch-all.  In that case there is the
 392      throw frame active, and this catch closure, so narrow by two
 393      frames.  */
 394   stack = scm_make_stack (SCM_BOOL_T, scm_list_1 (scm_from_int (2)));
 395   frame = scm_is_true (stack) ? scm_stack_ref (stack, SCM_INUM0) : SCM_BOOL_F;
 396
 397   if (should_print_backtrace (tag, stack))
 398     {
 399       scm_puts_unlocked ("Backtrace:\n", port);
 400       scm_display_backtrace_with_highlights (stack, port,
 401                                              SCM_BOOL_F, SCM_BOOL_F,
 402                                              SCM_EOL);
 403       scm_newline (port);
 404     }
 405
 406   scm_print_exception (port, frame, tag, args);
 407 }
 408
 409 \f
 410
 411 struct c_data {
 412   void *(*func) (void *);
 413   void *data;
 414   void *result;
 415 };
 416
 417 static SCM
 418 c_body (void *d)
 419 {
 420   struct c_data *data = (struct c_data *)d;
 421   data->result = data->func (data->data);
 422   return SCM_UNSPECIFIED;
 423 }
 424
 425 static SCM
 426 c_handler (void *d, SCM tag, SCM args)
 427 {
 428   struct c_data *data;
 429
 430   /* If TAG is `quit', exit() the process.  */
 431   if (scm_is_eq (tag, scm_from_latin1_symbol ("quit")))
 432     exit (scm_exit_status (args));
 433
 434   data = (struct c_data *)d;
 435   data->result = NULL;
 436   return SCM_UNSPECIFIED;
 437 }
 438
 439 static SCM
 440 pre_unwind_handler (void *error_port, SCM tag, SCM args)
 441 {
 442   /* Print the exception unless TAG is  `quit'.  */
 443   if (!scm_is_eq (tag, scm_from_latin1_symbol ("quit")))
 444     print_exception_and_backtrace (SCM_PACK_POINTER (error_port), tag, args);
 445
 446   return SCM_UNSPECIFIED;
 447 }
 448
 449 void *
 450 scm_c_with_continuation_barrier (void *(*func) (void *), void *data)
 451 {
 452   struct c_data c_data;
 453   c_data.func = func;
 454   c_data.data = data;
 455   scm_i_with_continuation_barrier (c_body, &c_data,
 456                                    c_handler, &c_data,
 457                                    pre_unwind_handler,
 458                                    SCM_UNPACK_POINTER (scm_current_error_port ()));
 459   return c_data.result;
 460 }
 461
 462 struct scm_data {
 463   SCM proc;
 464 };
 465
 466 static SCM
 467 scm_body (void *d)
 468 {
 469   struct scm_data *data = (struct scm_data *)d;
 470   return scm_call_0 (data->proc);
 471 }
 472
 473 static SCM
 474 scm_handler (void *d, SCM tag, SCM args)
 475 {
 476   /* Print a message.  Note that if TAG is `quit', this will exit() the
 477      process.  */
 478   scm_handle_by_message_noexit (NULL, tag, args);
 479
 480   return SCM_BOOL_F;
 481 }
 482
 483 SCM_DEFINE (scm_with_continuation_barrier, "with-continuation-barrier", 1,0,0,
 484             (SCM proc),
 485 "Call @var{proc} and return its result.  Do not allow the invocation of\n"
 486 "continuations that would leave or enter the dynamic extent of the call\n"
 487 "to @code{with-continuation-barrier}.  Such an attempt causes an error\n"
 488 "to be signaled.\n"
 489 "\n"
 490 "Throws (such as errors) that are not caught from within @var{proc} are\n"
 491 "caught by @code{with-continuation-barrier}.  In that case, a short\n"
 492 "message is printed to the current error port and @code{#f} is returned.\n"
 493 "\n"
 494 "Thus, @code{with-continuation-barrier} returns exactly once.\n")
 495 #define FUNC_NAME s_scm_with_continuation_barrier
 496 {
 497   struct scm_data scm_data;
 498   scm_data.proc = proc;
 499   return scm_i_with_continuation_barrier (scm_body, &scm_data,
 500                                           scm_handler, &scm_data,
 501                                           pre_unwind_handler,
 502                                           SCM_UNPACK_POINTER (scm_current_error_port ()));
 503 }
 504 #undef FUNC_NAME
 505
 506 void
 507 scm_init_continuations ()
 508 {
 509   tc16_continuation = scm_make_smob_type ("continuation", 0);
 510   scm_set_smob_print (tc16_continuation, continuation_print);
 511 #include "libguile/continuations.x"
 512 }
 513
 514 /*
 515   Local Variables:
 516   c-file-style: "gnu"
 517   End:
 518 */