libguile/continuations.c

   1 /* Copyright (C) 1995,1996,1998,2000,2001,2004, 2006 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
   5  * License as published by the Free Software Foundation; either
   6  * version 2.1 of the License, or (at your option) any later version.
   7  *
   8  * This library is distributed in the hope that it will be useful,
   9  * but 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 02110-1301 USA
  16  */
  17
  18
  19 \f
  20
  21 #include "libguile/_scm.h"
  22
  23 #include <string.h>
  24 #include <stdio.h>
  25
  26 #include "libguile/async.h"
  27 #include "libguile/debug.h"
  28 #include "libguile/root.h"
  29 #include "libguile/stackchk.h"
  30 #include "libguile/smob.h"
  31 #include "libguile/ports.h"
  32 #include "libguile/dynwind.h"
  33 #include "libguile/values.h"
  34 #include "libguile/eval.h"
  35
  36 #include "libguile/validate.h"
  37 #include "libguile/continuations.h"
  38
  39 \f
  40
  41 /* {Continuations}
  42  */
  43
  44 scm_t_bits scm_tc16_continuation;
  45
  46 static SCM
  47 continuation_mark (SCM obj)
  48 {
  49   scm_t_contregs *continuation = SCM_CONTREGS (obj);
  50
  51   scm_gc_mark (continuation->root);
  52   scm_gc_mark (continuation->throw_value);
  53   scm_mark_locations (continuation->stack, continuation->num_stack_items);
  54 #ifdef __ia64__
  55   if (continuation->backing_store)
  56     scm_mark_locations (continuation->backing_store,
  57                         continuation->backing_store_size /
  58                         sizeof (SCM_STACKITEM));
  59 #endif /* __ia64__ */
  60   return continuation->dynenv;
  61 }
  62
  63 static size_t
  64 continuation_free (SCM obj)
  65 {
  66   scm_t_contregs *continuation = SCM_CONTREGS (obj);
  67   /* stack array size is 1 if num_stack_items is 0.  */
  68   size_t extra_items = (continuation->num_stack_items > 0)
  69     ? (continuation->num_stack_items - 1)
  70     : 0;
  71   size_t bytes_free = sizeof (scm_t_contregs)
  72     + extra_items * sizeof (SCM_STACKITEM);
  73
  74 #ifdef __ia64__
  75   scm_gc_free (continuation->backing_store, continuation->backing_store_size,
  76                "continuation backing store");
  77 #endif /* __ia64__ */
  78   scm_gc_free (continuation, bytes_free, "continuation");
  79   return 0;
  80 }
  81
  82 static int
  83 continuation_print (SCM obj, SCM port, scm_print_state *state SCM_UNUSED)
  84 {
  85   scm_t_contregs *continuation = SCM_CONTREGS (obj);
  86
  87   scm_puts ("#<continuation ", port);
  88   scm_intprint (continuation->num_stack_items, 10, port);
  89   scm_puts (" @ ", port);
  90   scm_uintprint (SCM_CELL_WORD_1 (obj), 16, port);
  91   scm_putc ('>', port);
  92   return 1;
  93 }
  94
  95 /* this may return more than once: the first time with the escape
  96    procedure, then subsequently with the value to be passed to the
  97    continuation.  */
  98 #define FUNC_NAME "scm_make_continuation"
  99 SCM
 100 scm_make_continuation (int *first)
 101 {
 102   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 103   SCM cont;
 104   scm_t_contregs *continuation;
 105   long stack_size;
 106   SCM_STACKITEM * src;
 107
 108   SCM_FLUSH_REGISTER_WINDOWS;
 109   stack_size = scm_stack_size (thread->continuation_base);
 110   continuation = scm_gc_malloc (sizeof (scm_t_contregs)
 111                                 + (stack_size - 1) * sizeof (SCM_STACKITEM),
 112                                 "continuation");
 113   continuation->num_stack_items = stack_size;
 114   continuation->dynenv = scm_i_dynwinds ();
 115   continuation->throw_value = SCM_EOL;
 116   continuation->root = thread->continuation_root;
 117   continuation->dframe = scm_i_last_debug_frame ();
 118   src = thread->continuation_base;
 119   SCM_NEWSMOB (cont, scm_tc16_continuation, continuation);
 120
 121 #if ! SCM_STACK_GROWS_UP
 122   src -= stack_size;
 123 #endif
 124   continuation->offset = continuation->stack - src;
 125   memcpy (continuation->stack, src, sizeof (SCM_STACKITEM) * stack_size);
 126
 127 #ifdef __ia64__
 128   continuation->fresh = 1;
 129   getcontext (&continuation->ctx);
 130   if (continuation->fresh)
 131     {
 132       continuation->backing_store_size =
 133         (char *) scm_ia64_ar_bsp(&continuation->ctx)
 134         -
 135         (char *) scm_ia64_register_backing_store_base ();
 136       continuation->backing_store = NULL;
 137       continuation->backing_store =
 138         scm_gc_malloc (continuation->backing_store_size,
 139                        "continuation backing store");
 140       memcpy (continuation->backing_store,
 141               (void *) scm_ia64_register_backing_store_base (),
 142               continuation->backing_store_size);
 143       *first = 1;
 144       continuation->fresh = 0;
 145       return cont;
 146     }
 147   else
 148     {
 149       SCM ret = continuation->throw_value;
 150       *first = 0;
 151       continuation->throw_value = SCM_BOOL_F;
 152       return ret;
 153     }
 154 #else /* !__ia64__ */
 155   if (setjmp (continuation->jmpbuf))
 156     {
 157       SCM ret = continuation->throw_value;
 158       *first = 0;
 159       continuation->throw_value = SCM_BOOL_F;
 160       return ret;
 161     }
 162   else
 163     {
 164       *first = 1;
 165       return cont;
 166     }
 167 #endif /* !__ia64__ */
 168 }
 169 #undef FUNC_NAME
 170
 171
 172 /* Invoking a continuation proceeds as follows:
 173  *
 174  * - the stack is made large enough for the called continuation
 175  * - the old windchain is unwound down to the branching point
 176  * - the continuation stack is copied into place
 177  * - the windchain is rewound up to the continuation's context
 178  * - the continuation is invoked via longjmp (or setcontext)
 179  *
 180  * This order is important so that unwind and rewind handlers are run
 181  * with their correct stack.
 182  */
 183
 184 static void scm_dynthrow (SCM, SCM);
 185
 186 /* Grow the stack by a fixed amount to provide space to copy in the
 187  * continuation.  Possibly this function has to be called several times
 188  * recursively before enough space is available.  Make sure the compiler does
 189  * not optimize the growth array away by storing it's address into a global
 190  * variable.
 191  */
 192
 193 scm_t_bits scm_i_dummy;
 194
 195 static void
 196 grow_stack (SCM cont, SCM val)
 197 {
 198   scm_t_bits growth[100];
 199
 200   scm_i_dummy = (scm_t_bits) growth;
 201   scm_dynthrow (cont, val);
 202 }
 203
 204
 205 /* Copy the continuation stack into the current stack.  Calling functions from
 206  * within this function is safe, since only stack frames below this function's
 207  * own frame are overwritten.  Thus, memcpy can be used for best performance.
 208  */
 209
 210 typedef struct {
 211   scm_t_contregs *continuation;
 212   SCM_STACKITEM *dst;
 213 } copy_stack_data;
 214
 215 static void
 216 copy_stack (void *data)
 217 {
 218   copy_stack_data *d = (copy_stack_data *)data;
 219   memcpy (d->dst, d->continuation->stack,
 220           sizeof (SCM_STACKITEM) * d->continuation->num_stack_items);
 221 }
 222
 223 static void
 224 copy_stack_and_call (scm_t_contregs *continuation, SCM val,
 225                      SCM_STACKITEM * dst)
 226 {
 227   long delta;
 228   copy_stack_data data;
 229
 230   delta = scm_ilength (scm_i_dynwinds ()) - scm_ilength (continuation->dynenv);
 231   data.continuation = continuation;
 232   data.dst = dst;
 233   scm_i_dowinds (continuation->dynenv, delta, copy_stack, &data);
 234
 235   scm_i_set_last_debug_frame (continuation->dframe);
 236
 237   continuation->throw_value = val;
 238 #ifdef __ia64__
 239   memcpy (scm_ia64_register_backing_store_base (),
 240           continuation->backing_store,
 241           continuation->backing_store_size);
 242   setcontext (&continuation->ctx);
 243 #else
 244   longjmp (continuation->jmpbuf, 1);
 245 #endif
 246 }
 247
 248 /* Call grow_stack until the stack space is large enough, then, as the current
 249  * stack frame might get overwritten, let copy_stack_and_call perform the
 250  * actual copying and continuation calling.
 251  */
 252 static void
 253 scm_dynthrow (SCM cont, SCM val)
 254 {
 255   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 256   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 257   SCM_STACKITEM *dst = thread->continuation_base;
 258   SCM_STACKITEM stack_top_element;
 259
 260   if (scm_i_critical_section_level)
 261     {
 262       fprintf (stderr, "continuation invoked from within critical section.\n");
 263       abort ();
 264     }
 265
 266 #if SCM_STACK_GROWS_UP
 267   if (dst + continuation->num_stack_items >= &stack_top_element)
 268     grow_stack (cont, val);
 269 #else
 270   dst -= continuation->num_stack_items;
 271   if (dst <= &stack_top_element)
 272     grow_stack (cont, val);
 273 #endif /* def SCM_STACK_GROWS_UP */
 274
 275   SCM_FLUSH_REGISTER_WINDOWS;
 276   copy_stack_and_call (continuation, val, dst);
 277 }
 278
 279
 280 static SCM
 281 continuation_apply (SCM cont, SCM args)
 282 #define FUNC_NAME "continuation_apply"
 283 {
 284   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 285   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 286
 287   if (continuation->root != thread->continuation_root)
 288     {
 289       SCM_MISC_ERROR
 290         ("invoking continuation would cross continuation barrier: ~A",
 291          scm_list_1 (cont));
 292     }
 293
 294   scm_dynthrow (cont, scm_values (args));
 295   return SCM_UNSPECIFIED; /* not reached */
 296 }
 297 #undef FUNC_NAME
 298
 299 SCM
 300 scm_i_with_continuation_barrier (scm_t_catch_body body,
 301                                  void *body_data,
 302                                  scm_t_catch_handler handler,
 303                                  void *handler_data,
 304                                  scm_t_catch_handler pre_unwind_handler,
 305                                  void *pre_unwind_handler_data)
 306 {
 307   SCM_STACKITEM stack_item;
 308   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 309   SCM old_controot;
 310   SCM_STACKITEM *old_contbase;
 311   scm_t_debug_frame *old_lastframe;
 312   SCM result;
 313
 314   /* Establish a fresh continuation root.
 315    */
 316   old_controot = thread->continuation_root;
 317   old_contbase = thread->continuation_base;
 318   old_lastframe = thread->last_debug_frame;
 319   thread->continuation_root = scm_cons (thread->handle, old_controot);
 320   thread->continuation_base = &stack_item;
 321   thread->last_debug_frame = NULL;
 322
 323   /* Call FUNC inside a catch all.  This is now guaranteed to return
 324      directly and exactly once.
 325   */
 326   result = scm_c_catch (SCM_BOOL_T,
 327                         body, body_data,
 328                         handler, handler_data,
 329                         pre_unwind_handler, pre_unwind_handler_data);
 330
 331   /* Return to old continuation root.
 332    */
 333   thread->last_debug_frame = old_lastframe;
 334   thread->continuation_base = old_contbase;
 335   thread->continuation_root = old_controot;
 336
 337   return result;
 338 }
 339
 340 struct c_data {
 341   void *(*func) (void *);
 342   void *data;
 343   void *result;
 344 };
 345
 346 static SCM
 347 c_body (void *d)
 348 {
 349   struct c_data *data = (struct c_data *)d;
 350   data->result = data->func (data->data);
 351   return SCM_UNSPECIFIED;
 352 }
 353
 354 static SCM
 355 c_handler (void *d, SCM tag, SCM args)
 356 {
 357   struct c_data *data = (struct c_data *)d;
 358   data->result = NULL;
 359   return SCM_UNSPECIFIED;
 360 }
 361
 362 void *
 363 scm_c_with_continuation_barrier (void *(*func) (void *), void *data)
 364 {
 365   struct c_data c_data;
 366   c_data.func = func;
 367   c_data.data = data;
 368   scm_i_with_continuation_barrier (c_body, &c_data,
 369                                    c_handler, &c_data,
 370                                    scm_handle_by_message_noexit, NULL);
 371   return c_data.result;
 372 }
 373
 374 struct scm_data {
 375   SCM proc;
 376 };
 377
 378 static SCM
 379 scm_body (void *d)
 380 {
 381   struct scm_data *data = (struct scm_data *)d;
 382   return scm_call_0 (data->proc);
 383 }
 384
 385 static SCM
 386 scm_handler (void *d, SCM tag, SCM args)
 387 {
 388   return SCM_BOOL_F;
 389 }
 390
 391 SCM_DEFINE (scm_with_continuation_barrier, "with-continuation-barrier", 1,0,0,
 392             (SCM proc),
 393 "Call @var{proc} and return its result.  Do not allow the invocation of\n"
 394 "continuations that would leave or enter the dynamic extent of the call\n"
 395 "to @code{with-continuation-barrier}.  Such an attempt causes an error\n"
 396 "to be signaled.\n"
 397 "\n"
 398 "Throws (such as errors) that are not caught from within @var{proc} are\n"
 399 "caught by @code{with-continuation-barrier}.  In that case, a short\n"
 400 "message is printed to the current error port and @code{#f} is returned.\n"
 401 "\n"
 402 "Thus, @code{with-continuation-barrier} returns exactly once.\n")
 403 #define FUNC_NAME s_scm_with_continuation_barrier
 404 {
 405   struct scm_data scm_data;
 406   scm_data.proc = proc;
 407   return scm_i_with_continuation_barrier (scm_body, &scm_data,
 408                                           scm_handler, &scm_data,
 409                                           scm_handle_by_message_noexit, NULL);
 410 }
 411 #undef FUNC_NAME
 412
 413 void
 414 scm_init_continuations ()
 415 {
 416   scm_tc16_continuation = scm_make_smob_type ("continuation", 0);
 417   scm_set_smob_mark (scm_tc16_continuation, continuation_mark);
 418   scm_set_smob_free (scm_tc16_continuation, continuation_free);
 419   scm_set_smob_print (scm_tc16_continuation, continuation_print);
 420   scm_set_smob_apply (scm_tc16_continuation, continuation_apply, 0, 0, 1);
 421 #include "libguile/continuations.x"
 422 }
 423
 424 /*
 425   Local Variables:
 426   c-file-style: "gnu"
 427   End:
 428 */