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, struct scm_vm *vp, 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->vp = vp;
 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 (SCM_VM_FRAME_KIND_CONT, data,
 181                                (data->fp + data->reloc) - data->stack_base,
 182                                (data->sp + data->reloc) - data->stack_base,
 183                                data->ra);
 184     }
 185   else
 186     return SCM_BOOL_F;
 187 }
 188
 189 struct scm_vm *
 190 scm_i_contregs_vp (SCM contregs)
 191 {
 192   return SCM_CONTREGS (contregs)->vp;
 193 }
 194
 195 SCM
 196 scm_i_contregs_vm_cont (SCM contregs)
 197 {
 198   return SCM_CONTREGS (contregs)->vm_cont;
 199 }
 200
 201
 202 /* {Apply}
 203  */
 204
 205 /* Invoking a continuation proceeds as follows:
 206  *
 207  * - the stack is made large enough for the called continuation
 208  * - the old windchain is unwound down to the branching point
 209  * - the continuation stack is copied into place
 210  * - the windchain is rewound up to the continuation's context
 211  * - the continuation is invoked via longjmp (or setcontext)
 212  *
 213  * This order is important so that unwind and rewind handlers are run
 214  * with their correct stack.
 215  */
 216
 217 static void scm_dynthrow (SCM);
 218
 219 /* Grow the stack by a fixed amount to provide space to copy in the
 220  * continuation.  Possibly this function has to be called several times
 221  * recursively before enough space is available.  Make sure the compiler does
 222  * not optimize the growth array away by storing it's address into a global
 223  * variable.
 224  */
 225
 226 static scm_t_bits scm_i_dummy;
 227
 228 static void
 229 grow_stack (SCM cont)
 230 {
 231   scm_t_bits growth[100];
 232
 233   scm_i_dummy = (scm_t_bits) growth;
 234   scm_dynthrow (cont);
 235 }
 236
 237
 238 /* Copy the continuation stack into the current stack.  Calling functions from
 239  * within this function is safe, since only stack frames below this function's
 240  * own frame are overwritten.  Thus, memcpy can be used for best performance.
 241  */
 242
 243 static void
 244 copy_stack_and_call (scm_t_contregs *continuation,
 245                      SCM_STACKITEM * dst)
 246 {
 247   scm_t_dynstack *dynstack;
 248   scm_t_bits *joint;
 249   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 250
 251   dynstack = SCM_VM_CONT_DATA (continuation->vm_cont)->dynstack;
 252
 253   joint = scm_dynstack_unwind_fork (&thread->dynstack, dynstack);
 254
 255   memcpy (dst, continuation->stack,
 256           sizeof (SCM_STACKITEM) * continuation->num_stack_items);
 257 #ifdef __ia64__
 258   thread->pending_rbs_continuation = continuation;
 259 #endif
 260
 261   scm_dynstack_wind (&thread->dynstack, joint);
 262
 263   SCM_I_LONGJMP (continuation->jmpbuf, 1);
 264 }
 265
 266 #ifdef __ia64__
 267 void
 268 scm_ia64_longjmp (scm_i_jmp_buf *JB, int VAL)
 269 {
 270   scm_i_thread *t = SCM_I_CURRENT_THREAD;
 271
 272   if (t->pending_rbs_continuation)
 273     {
 274       memcpy (t->register_backing_store_base,
 275               t->pending_rbs_continuation->backing_store,
 276               t->pending_rbs_continuation->backing_store_size);
 277       t->pending_rbs_continuation = NULL;
 278     }
 279   setcontext (&JB->ctx);
 280 }
 281 #endif
 282
 283 /* Call grow_stack until the stack space is large enough, then, as the current
 284  * stack frame might get overwritten, let copy_stack_and_call perform the
 285  * actual copying and continuation calling.
 286  */
 287 static void
 288 scm_dynthrow (SCM cont)
 289 {
 290   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 291   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 292   SCM_STACKITEM *dst = thread->continuation_base;
 293   SCM_STACKITEM stack_top_element;
 294
 295   if (thread->critical_section_level)
 296     {
 297       fprintf (stderr, "continuation invoked from within critical section.\n");
 298       abort ();
 299     }
 300
 301 #if SCM_STACK_GROWS_UP
 302   if (dst + continuation->num_stack_items >= &stack_top_element)
 303     grow_stack (cont);
 304 #else
 305   dst -= continuation->num_stack_items;
 306   if (dst <= &stack_top_element)
 307     grow_stack (cont);
 308 #endif /* def SCM_STACK_GROWS_UP */
 309
 310   SCM_FLUSH_REGISTER_WINDOWS;
 311   copy_stack_and_call (continuation, dst);
 312 }
 313
 314
 315 void
 316 scm_i_check_continuation (SCM cont)
 317 {
 318   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 319   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 320
 321   if (!scm_is_eq (continuation->root, thread->continuation_root))
 322     scm_misc_error
 323       ("%continuation-call",
 324        "invoking continuation would cross continuation barrier: ~A",
 325        scm_list_1 (cont));
 326 }
 327
 328 void
 329 scm_i_reinstate_continuation (SCM cont)
 330 {
 331   scm_dynthrow (cont);
 332 }
 333
 334 SCM
 335 scm_i_with_continuation_barrier (scm_t_catch_body body,
 336                                  void *body_data,
 337                                  scm_t_catch_handler handler,
 338                                  void *handler_data,
 339                                  scm_t_catch_handler pre_unwind_handler,
 340                                  void *pre_unwind_handler_data)
 341 {
 342   SCM_STACKITEM stack_item;
 343   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 344   SCM old_controot;
 345   SCM_STACKITEM *old_contbase;
 346   SCM result;
 347
 348   /* Establish a fresh continuation root.
 349    */
 350   old_controot = thread->continuation_root;
 351   old_contbase = thread->continuation_base;
 352   thread->continuation_root = scm_cons (thread->handle, old_controot);
 353   thread->continuation_base = &stack_item;
 354
 355   /* Call FUNC inside a catch all.  This is now guaranteed to return
 356      directly and exactly once.
 357   */
 358   result = scm_c_catch (SCM_BOOL_T,
 359                         body, body_data,
 360                         handler, handler_data,
 361                         pre_unwind_handler, pre_unwind_handler_data);
 362
 363   /* Return to old continuation root.
 364    */
 365   thread->continuation_base = old_contbase;
 366   thread->continuation_root = old_controot;
 367
 368   return result;
 369 }
 370
 371 \f
 372
 373 static int
 374 should_print_backtrace (SCM tag, SCM stack)
 375 {
 376   return SCM_BACKTRACE_P
 377     && scm_is_true (stack)
 378     && scm_initialized_p
 379     /* It's generally not useful to print backtraces for errors reading
 380        or expanding code in these fallback catch statements. */
 381     && !scm_is_eq (tag, scm_from_latin1_symbol ("read-error"))
 382     && !scm_is_eq (tag, scm_from_latin1_symbol ("syntax-error"));
 383 }
 384
 385 static void
 386 print_exception_and_backtrace (SCM port, SCM tag, SCM args)
 387 {
 388   SCM stack, frame;
 389
 390   /* We get here via a throw to a catch-all.  In that case there is the
 391      throw frame active, and this catch closure, so narrow by two
 392      frames.  */
 393   stack = scm_make_stack (SCM_BOOL_T, scm_list_1 (scm_from_int (2)));
 394   frame = scm_is_true (stack) ? scm_stack_ref (stack, SCM_INUM0) : SCM_BOOL_F;
 395
 396   if (should_print_backtrace (tag, stack))
 397     {
 398       scm_puts_unlocked ("Backtrace:\n", port);
 399       scm_display_backtrace_with_highlights (stack, port,
 400                                              SCM_BOOL_F, SCM_BOOL_F,
 401                                              SCM_EOL);
 402       scm_newline (port);
 403     }
 404
 405   scm_print_exception (port, frame, tag, args);
 406 }
 407
 408 \f
 409
 410 struct c_data {
 411   void *(*func) (void *);
 412   void *data;
 413   void *result;
 414 };
 415
 416 static SCM
 417 c_body (void *d)
 418 {
 419   struct c_data *data = (struct c_data *)d;
 420   data->result = data->func (data->data);
 421   return SCM_UNSPECIFIED;
 422 }
 423
 424 static SCM
 425 c_handler (void *d, SCM tag, SCM args)
 426 {
 427   struct c_data *data;
 428
 429   /* If TAG is `quit', exit() the process.  */
 430   if (scm_is_eq (tag, scm_from_latin1_symbol ("quit")))
 431     exit (scm_exit_status (args));
 432
 433   data = (struct c_data *)d;
 434   data->result = NULL;
 435   return SCM_UNSPECIFIED;
 436 }
 437
 438 static SCM
 439 pre_unwind_handler (void *error_port, SCM tag, SCM args)
 440 {
 441   /* Print the exception unless TAG is  `quit'.  */
 442   if (!scm_is_eq (tag, scm_from_latin1_symbol ("quit")))
 443     print_exception_and_backtrace (SCM_PACK_POINTER (error_port), tag, args);
 444
 445   return SCM_UNSPECIFIED;
 446 }
 447
 448 void *
 449 scm_c_with_continuation_barrier (void *(*func) (void *), void *data)
 450 {
 451   struct c_data c_data;
 452   c_data.func = func;
 453   c_data.data = data;
 454   scm_i_with_continuation_barrier (c_body, &c_data,
 455                                    c_handler, &c_data,
 456                                    pre_unwind_handler,
 457                                    SCM_UNPACK_POINTER (scm_current_error_port ()));
 458   return c_data.result;
 459 }
 460
 461 struct scm_data {
 462   SCM proc;
 463 };
 464
 465 static SCM
 466 scm_body (void *d)
 467 {
 468   struct scm_data *data = (struct scm_data *)d;
 469   return scm_call_0 (data->proc);
 470 }
 471
 472 static SCM
 473 scm_handler (void *d, SCM tag, SCM args)
 474 {
 475   /* Print a message.  Note that if TAG is `quit', this will exit() the
 476      process.  */
 477   scm_handle_by_message_noexit (NULL, tag, args);
 478
 479   return SCM_BOOL_F;
 480 }
 481
 482 SCM_DEFINE (scm_with_continuation_barrier, "with-continuation-barrier", 1,0,0,
 483             (SCM proc),
 484 "Call @var{proc} and return its result.  Do not allow the invocation of\n"
 485 "continuations that would leave or enter the dynamic extent of the call\n"
 486 "to @code{with-continuation-barrier}.  Such an attempt causes an error\n"
 487 "to be signaled.\n"
 488 "\n"
 489 "Throws (such as errors) that are not caught from within @var{proc} are\n"
 490 "caught by @code{with-continuation-barrier}.  In that case, a short\n"
 491 "message is printed to the current error port and @code{#f} is returned.\n"
 492 "\n"
 493 "Thus, @code{with-continuation-barrier} returns exactly once.\n")
 494 #define FUNC_NAME s_scm_with_continuation_barrier
 495 {
 496   struct scm_data scm_data;
 497   scm_data.proc = proc;
 498   return scm_i_with_continuation_barrier (scm_body, &scm_data,
 499                                           scm_handler, &scm_data,
 500                                           pre_unwind_handler,
 501                                           SCM_UNPACK_POINTER (scm_current_error_port ()));
 502 }
 503 #undef FUNC_NAME
 504
 505 void
 506 scm_init_continuations ()
 507 {
 508   tc16_continuation = scm_make_smob_type ("continuation", 0);
 509   scm_set_smob_print (tc16_continuation, continuation_print);
 510 #include "libguile/continuations.x"
 511 }
 512
 513 /*
 514   Local Variables:
 515   c-file-style: "gnu"
 516   End:
 517 */