libguile/continuations.c

   1 /* Copyright (C) 1995,1996,1998,2000,2001,2004, 2006, 2008, 2009, 2010, 2011, 2012, 2013, 2014 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     {
 165       scm_gc_after_nonlocal_exit ();
 166       return SCM_UNDEFINED;
 167     }
 168 }
 169 #undef FUNC_NAME
 170
 171 int
 172 scm_i_continuation_to_frame (SCM continuation, struct scm_frame *frame)
 173 {
 174   SCM contregs;
 175   scm_t_contregs *cont;
 176
 177   contregs = SCM_PROGRAM_FREE_VARIABLE_REF (continuation, 0);
 178   cont = SCM_CONTREGS (contregs);
 179
 180   if (scm_is_true (cont->vm_cont))
 181     {
 182       struct scm_vm_cont *data = SCM_VM_CONT_DATA (cont->vm_cont);
 183
 184       frame->stack_holder = data;
 185       frame->fp_offset = (data->fp + data->reloc) - data->stack_base;
 186       frame->sp_offset = (data->sp + data->reloc) - data->stack_base;
 187       frame->ip = data->ra;
 188
 189       return 1;
 190     }
 191   else
 192     return 0;
 193 }
 194
 195 struct scm_vm *
 196 scm_i_contregs_vp (SCM contregs)
 197 {
 198   return SCM_CONTREGS (contregs)->vp;
 199 }
 200
 201 SCM
 202 scm_i_contregs_vm_cont (SCM contregs)
 203 {
 204   return SCM_CONTREGS (contregs)->vm_cont;
 205 }
 206
 207
 208 /* {Apply}
 209  */
 210
 211 /* Invoking a continuation proceeds as follows:
 212  *
 213  * - the stack is made large enough for the called continuation
 214  * - the old windchain is unwound down to the branching point
 215  * - the continuation stack is copied into place
 216  * - the windchain is rewound up to the continuation's context
 217  * - the continuation is invoked via longjmp (or setcontext)
 218  *
 219  * This order is important so that unwind and rewind handlers are run
 220  * with their correct stack.
 221  */
 222
 223 static void scm_dynthrow (SCM);
 224
 225 /* Grow the stack by a fixed amount to provide space to copy in the
 226  * continuation.  Possibly this function has to be called several times
 227  * recursively before enough space is available.  Make sure the compiler does
 228  * not optimize the growth array away by storing it's address into a global
 229  * variable.
 230  */
 231
 232 static scm_t_bits scm_i_dummy;
 233
 234 static void
 235 grow_stack (SCM cont)
 236 {
 237   scm_t_bits growth[100];
 238
 239   scm_i_dummy = (scm_t_bits) growth;
 240   scm_dynthrow (cont);
 241 }
 242
 243
 244 /* Copy the continuation stack into the current stack.  Calling functions from
 245  * within this function is safe, since only stack frames below this function's
 246  * own frame are overwritten.  Thus, memcpy can be used for best performance.
 247  */
 248
 249 static void
 250 copy_stack_and_call (scm_t_contregs *continuation,
 251                      SCM_STACKITEM * dst)
 252 {
 253   scm_t_dynstack *dynstack;
 254   scm_t_bits *joint;
 255   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 256
 257   dynstack = SCM_VM_CONT_DATA (continuation->vm_cont)->dynstack;
 258
 259   joint = scm_dynstack_unwind_fork (&thread->dynstack, dynstack);
 260
 261   memcpy (dst, continuation->stack,
 262           sizeof (SCM_STACKITEM) * continuation->num_stack_items);
 263 #ifdef __ia64__
 264   thread->pending_rbs_continuation = continuation;
 265 #endif
 266
 267   scm_dynstack_wind (&thread->dynstack, joint);
 268
 269   SCM_I_LONGJMP (continuation->jmpbuf, 1);
 270 }
 271
 272 #ifdef __ia64__
 273 void
 274 scm_ia64_longjmp (scm_i_jmp_buf *JB, int VAL)
 275 {
 276   scm_i_thread *t = SCM_I_CURRENT_THREAD;
 277
 278   if (t->pending_rbs_continuation)
 279     {
 280       memcpy (t->register_backing_store_base,
 281               t->pending_rbs_continuation->backing_store,
 282               t->pending_rbs_continuation->backing_store_size);
 283       t->pending_rbs_continuation = NULL;
 284     }
 285   setcontext (&JB->ctx);
 286 }
 287 #endif
 288
 289 /* Call grow_stack until the stack space is large enough, then, as the current
 290  * stack frame might get overwritten, let copy_stack_and_call perform the
 291  * actual copying and continuation calling.
 292  */
 293 static void
 294 scm_dynthrow (SCM cont)
 295 {
 296   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 297   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 298   SCM_STACKITEM *dst = thread->continuation_base;
 299   SCM_STACKITEM stack_top_element;
 300
 301   if (thread->critical_section_level)
 302     {
 303       fprintf (stderr, "continuation invoked from within critical section.\n");
 304       abort ();
 305     }
 306
 307 #if SCM_STACK_GROWS_UP
 308   if (dst + continuation->num_stack_items >= &stack_top_element)
 309     grow_stack (cont);
 310 #else
 311   dst -= continuation->num_stack_items;
 312   if (dst <= &stack_top_element)
 313     grow_stack (cont);
 314 #endif /* def SCM_STACK_GROWS_UP */
 315
 316   SCM_FLUSH_REGISTER_WINDOWS;
 317   copy_stack_and_call (continuation, dst);
 318 }
 319
 320
 321 void
 322 scm_i_check_continuation (SCM cont)
 323 {
 324   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 325   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 326
 327   if (!scm_is_eq (continuation->root, thread->continuation_root))
 328     scm_misc_error
 329       ("%continuation-call",
 330        "invoking continuation would cross continuation barrier: ~A",
 331        scm_list_1 (cont));
 332 }
 333
 334 void
 335 scm_i_reinstate_continuation (SCM cont)
 336 {
 337   scm_dynthrow (cont);
 338 }
 339
 340 SCM
 341 scm_i_with_continuation_barrier (scm_t_catch_body body,
 342                                  void *body_data,
 343                                  scm_t_catch_handler handler,
 344                                  void *handler_data,
 345                                  scm_t_catch_handler pre_unwind_handler,
 346                                  void *pre_unwind_handler_data)
 347 {
 348   SCM_STACKITEM stack_item;
 349   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 350   SCM old_controot;
 351   SCM_STACKITEM *old_contbase;
 352   SCM result;
 353
 354   /* Establish a fresh continuation root.
 355    */
 356   old_controot = thread->continuation_root;
 357   old_contbase = thread->continuation_base;
 358   thread->continuation_root = scm_cons (thread->handle, old_controot);
 359   thread->continuation_base = &stack_item;
 360
 361   /* Call FUNC inside a catch all.  This is now guaranteed to return
 362      directly and exactly once.
 363   */
 364   result = scm_c_catch (SCM_BOOL_T,
 365                         body, body_data,
 366                         handler, handler_data,
 367                         pre_unwind_handler, pre_unwind_handler_data);
 368
 369   /* Return to old continuation root.
 370    */
 371   thread->continuation_base = old_contbase;
 372   thread->continuation_root = old_controot;
 373
 374   return result;
 375 }
 376
 377 \f
 378
 379 static int
 380 should_print_backtrace (SCM tag, SCM stack)
 381 {
 382   return SCM_BACKTRACE_P
 383     && scm_is_true (stack)
 384     && scm_initialized_p
 385     /* It's generally not useful to print backtraces for errors reading
 386        or expanding code in these fallback catch statements. */
 387     && !scm_is_eq (tag, scm_from_latin1_symbol ("read-error"))
 388     && !scm_is_eq (tag, scm_from_latin1_symbol ("syntax-error"));
 389 }
 390
 391 static void
 392 print_exception_and_backtrace (SCM port, SCM tag, SCM args)
 393 {
 394   SCM stack, frame;
 395
 396   /* We get here via a throw to a catch-all.  In that case there is the
 397      throw frame active, and this catch closure, so narrow by two
 398      frames.  */
 399   stack = scm_make_stack (SCM_BOOL_T, scm_list_1 (scm_from_int (2)));
 400   frame = scm_is_true (stack) ? scm_stack_ref (stack, SCM_INUM0) : SCM_BOOL_F;
 401
 402   if (should_print_backtrace (tag, stack))
 403     {
 404       scm_puts_unlocked ("Backtrace:\n", port);
 405       scm_display_backtrace_with_highlights (stack, port,
 406                                              SCM_BOOL_F, SCM_BOOL_F,
 407                                              SCM_EOL);
 408       scm_newline (port);
 409     }
 410
 411   scm_print_exception (port, frame, tag, args);
 412 }
 413
 414 \f
 415
 416 struct c_data {
 417   void *(*func) (void *);
 418   void *data;
 419   void *result;
 420 };
 421
 422 static SCM
 423 c_body (void *d)
 424 {
 425   struct c_data *data = (struct c_data *)d;
 426   data->result = data->func (data->data);
 427   return SCM_UNSPECIFIED;
 428 }
 429
 430 static SCM
 431 c_handler (void *d, SCM tag, SCM args)
 432 {
 433   struct c_data *data;
 434
 435   /* If TAG is `quit', exit() the process.  */
 436   if (scm_is_eq (tag, scm_from_latin1_symbol ("quit")))
 437     exit (scm_exit_status (args));
 438
 439   data = (struct c_data *)d;
 440   data->result = NULL;
 441   return SCM_UNSPECIFIED;
 442 }
 443
 444 static SCM
 445 pre_unwind_handler (void *error_port, SCM tag, SCM args)
 446 {
 447   /* Print the exception unless TAG is  `quit'.  */
 448   if (!scm_is_eq (tag, scm_from_latin1_symbol ("quit")))
 449     print_exception_and_backtrace (SCM_PACK_POINTER (error_port), tag, args);
 450
 451   return SCM_UNSPECIFIED;
 452 }
 453
 454 void *
 455 scm_c_with_continuation_barrier (void *(*func) (void *), void *data)
 456 {
 457   struct c_data c_data;
 458   c_data.func = func;
 459   c_data.data = data;
 460   scm_i_with_continuation_barrier (c_body, &c_data,
 461                                    c_handler, &c_data,
 462                                    pre_unwind_handler,
 463                                    SCM_UNPACK_POINTER (scm_current_error_port ()));
 464   return c_data.result;
 465 }
 466
 467 struct scm_data {
 468   SCM proc;
 469 };
 470
 471 static SCM
 472 scm_body (void *d)
 473 {
 474   struct scm_data *data = (struct scm_data *)d;
 475   return scm_call_0 (data->proc);
 476 }
 477
 478 static SCM
 479 scm_handler (void *d, SCM tag, SCM args)
 480 {
 481   /* Print a message.  Note that if TAG is `quit', this will exit() the
 482      process.  */
 483   scm_handle_by_message_noexit (NULL, tag, args);
 484
 485   return SCM_BOOL_F;
 486 }
 487
 488 SCM_DEFINE (scm_with_continuation_barrier, "with-continuation-barrier", 1,0,0,
 489             (SCM proc),
 490 "Call @var{proc} and return its result.  Do not allow the invocation of\n"
 491 "continuations that would leave or enter the dynamic extent of the call\n"
 492 "to @code{with-continuation-barrier}.  Such an attempt causes an error\n"
 493 "to be signaled.\n"
 494 "\n"
 495 "Throws (such as errors) that are not caught from within @var{proc} are\n"
 496 "caught by @code{with-continuation-barrier}.  In that case, a short\n"
 497 "message is printed to the current error port and @code{#f} is returned.\n"
 498 "\n"
 499 "Thus, @code{with-continuation-barrier} returns exactly once.\n")
 500 #define FUNC_NAME s_scm_with_continuation_barrier
 501 {
 502   struct scm_data scm_data;
 503   scm_data.proc = proc;
 504   return scm_i_with_continuation_barrier (scm_body, &scm_data,
 505                                           scm_handler, &scm_data,
 506                                           pre_unwind_handler,
 507                                           SCM_UNPACK_POINTER (scm_current_error_port ()));
 508 }
 509 #undef FUNC_NAME
 510
 511 void
 512 scm_init_continuations ()
 513 {
 514   tc16_continuation = scm_make_smob_type ("continuation", 0);
 515   scm_set_smob_print (tc16_continuation, continuation_print);
 516 #include "libguile/continuations.x"
 517 }
 518
 519 /*
 520   Local Variables:
 521   c-file-style: "gnu"
 522   End:
 523 */