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   *first = !setjmp (continuation->jmpbuf);
 128   if (*first)
 129     {
 130 #ifdef __ia64__
 131       continuation->backing_store_size =
 132         (char *) scm_ia64_ar_bsp(&continuation->jmpbuf.ctx)
 133         -
 134         (char *) thread->register_backing_store_base;
 135       continuation->backing_store = NULL;
 136       continuation->backing_store =
 137         scm_gc_malloc (continuation->backing_store_size,
 138                        "continuation backing store");
 139       memcpy (continuation->backing_store,
 140               (void *) thread->register_backing_store_base,
 141               continuation->backing_store_size);
 142 #endif /* __ia64__ */
 143       return cont;
 144     }
 145   else
 146     {
 147       SCM ret = continuation->throw_value;
 148       continuation->throw_value = SCM_BOOL_F;
 149       return ret;
 150     }
 151 }
 152 #undef FUNC_NAME
 153
 154
 155 /* Invoking a continuation proceeds as follows:
 156  *
 157  * - the stack is made large enough for the called continuation
 158  * - the old windchain is unwound down to the branching point
 159  * - the continuation stack is copied into place
 160  * - the windchain is rewound up to the continuation's context
 161  * - the continuation is invoked via longjmp (or setcontext)
 162  *
 163  * This order is important so that unwind and rewind handlers are run
 164  * with their correct stack.
 165  */
 166
 167 static void scm_dynthrow (SCM, SCM);
 168
 169 /* Grow the stack by a fixed amount to provide space to copy in the
 170  * continuation.  Possibly this function has to be called several times
 171  * recursively before enough space is available.  Make sure the compiler does
 172  * not optimize the growth array away by storing it's address into a global
 173  * variable.
 174  */
 175
 176 scm_t_bits scm_i_dummy;
 177
 178 static void
 179 grow_stack (SCM cont, SCM val)
 180 {
 181   scm_t_bits growth[100];
 182
 183   scm_i_dummy = (scm_t_bits) growth;
 184   scm_dynthrow (cont, val);
 185 }
 186
 187
 188 /* Copy the continuation stack into the current stack.  Calling functions from
 189  * within this function is safe, since only stack frames below this function's
 190  * own frame are overwritten.  Thus, memcpy can be used for best performance.
 191  */
 192
 193 typedef struct {
 194   scm_t_contregs *continuation;
 195   SCM_STACKITEM *dst;
 196 } copy_stack_data;
 197
 198 static void
 199 copy_stack (void *data)
 200 {
 201   copy_stack_data *d = (copy_stack_data *)data;
 202   memcpy (d->dst, d->continuation->stack,
 203           sizeof (SCM_STACKITEM) * d->continuation->num_stack_items);
 204 #ifdef __ia64__
 205   SCM_I_CURRENT_THREAD->pending_rbs_continuation = d->continuation;
 206 #endif
 207 }
 208
 209 static void
 210 copy_stack_and_call (scm_t_contregs *continuation, SCM val,
 211                      SCM_STACKITEM * dst)
 212 {
 213   long delta;
 214   copy_stack_data data;
 215
 216   delta = scm_ilength (scm_i_dynwinds ()) - scm_ilength (continuation->dynenv);
 217   data.continuation = continuation;
 218   data.dst = dst;
 219   scm_i_dowinds (continuation->dynenv, delta, copy_stack, &data);
 220
 221   scm_i_set_last_debug_frame (continuation->dframe);
 222
 223   continuation->throw_value = val;
 224   longjmp (continuation->jmpbuf, 1);
 225 }
 226
 227 #ifdef __ia64__
 228 void
 229 scm_ia64_longjmp (jmp_buf *JB, int VAL)
 230 {
 231   scm_i_thread *t = SCM_I_CURRENT_THREAD;
 232
 233   if (t->pending_rbs_continuation)
 234     {
 235       memcpy (t->register_backing_store_base,
 236               t->pending_rbs_continuation->backing_store,
 237               t->pending_rbs_continuation->backing_store_size);
 238       t->pending_rbs_continuation = NULL;
 239     }
 240   setcontext (&JB->ctx);
 241 }
 242 #endif
 243
 244 /* Call grow_stack until the stack space is large enough, then, as the current
 245  * stack frame might get overwritten, let copy_stack_and_call perform the
 246  * actual copying and continuation calling.
 247  */
 248 static void
 249 scm_dynthrow (SCM cont, SCM val)
 250 {
 251   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 252   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 253   SCM_STACKITEM *dst = thread->continuation_base;
 254   SCM_STACKITEM stack_top_element;
 255
 256   if (scm_i_critical_section_level)
 257     {
 258       fprintf (stderr, "continuation invoked from within critical section.\n");
 259       abort ();
 260     }
 261
 262 #if SCM_STACK_GROWS_UP
 263   if (dst + continuation->num_stack_items >= &stack_top_element)
 264     grow_stack (cont, val);
 265 #else
 266   dst -= continuation->num_stack_items;
 267   if (dst <= &stack_top_element)
 268     grow_stack (cont, val);
 269 #endif /* def SCM_STACK_GROWS_UP */
 270
 271   SCM_FLUSH_REGISTER_WINDOWS;
 272   copy_stack_and_call (continuation, val, dst);
 273 }
 274
 275
 276 static SCM
 277 continuation_apply (SCM cont, SCM args)
 278 #define FUNC_NAME "continuation_apply"
 279 {
 280   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 281   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 282
 283   if (continuation->root != thread->continuation_root)
 284     {
 285       SCM_MISC_ERROR
 286         ("invoking continuation would cross continuation barrier: ~A",
 287          scm_list_1 (cont));
 288     }
 289
 290   scm_dynthrow (cont, scm_values (args));
 291   return SCM_UNSPECIFIED; /* not reached */
 292 }
 293 #undef FUNC_NAME
 294
 295 SCM
 296 scm_i_with_continuation_barrier (scm_t_catch_body body,
 297                                  void *body_data,
 298                                  scm_t_catch_handler handler,
 299                                  void *handler_data,
 300                                  scm_t_catch_handler pre_unwind_handler,
 301                                  void *pre_unwind_handler_data)
 302 {
 303   SCM_STACKITEM stack_item;
 304   scm_i_thread *thread = SCM_I_CURRENT_THREAD;
 305   SCM old_controot;
 306   SCM_STACKITEM *old_contbase;
 307   scm_t_debug_frame *old_lastframe;
 308   SCM result;
 309
 310   /* Establish a fresh continuation root.
 311    */
 312   old_controot = thread->continuation_root;
 313   old_contbase = thread->continuation_base;
 314   old_lastframe = thread->last_debug_frame;
 315   thread->continuation_root = scm_cons (thread->handle, old_controot);
 316   thread->continuation_base = &stack_item;
 317   thread->last_debug_frame = NULL;
 318
 319   /* Call FUNC inside a catch all.  This is now guaranteed to return
 320      directly and exactly once.
 321   */
 322   result = scm_c_catch (SCM_BOOL_T,
 323                         body, body_data,
 324                         handler, handler_data,
 325                         pre_unwind_handler, pre_unwind_handler_data);
 326
 327   /* Return to old continuation root.
 328    */
 329   thread->last_debug_frame = old_lastframe;
 330   thread->continuation_base = old_contbase;
 331   thread->continuation_root = old_controot;
 332
 333   return result;
 334 }
 335
 336 struct c_data {
 337   void *(*func) (void *);
 338   void *data;
 339   void *result;
 340 };
 341
 342 static SCM
 343 c_body (void *d)
 344 {
 345   struct c_data *data = (struct c_data *)d;
 346   data->result = data->func (data->data);
 347   return SCM_UNSPECIFIED;
 348 }
 349
 350 static SCM
 351 c_handler (void *d, SCM tag, SCM args)
 352 {
 353   struct c_data *data = (struct c_data *)d;
 354   data->result = NULL;
 355   return SCM_UNSPECIFIED;
 356 }
 357
 358 void *
 359 scm_c_with_continuation_barrier (void *(*func) (void *), void *data)
 360 {
 361   struct c_data c_data;
 362   c_data.func = func;
 363   c_data.data = data;
 364   scm_i_with_continuation_barrier (c_body, &c_data,
 365                                    c_handler, &c_data,
 366                                    scm_handle_by_message_noexit, NULL);
 367   return c_data.result;
 368 }
 369
 370 struct scm_data {
 371   SCM proc;
 372 };
 373
 374 static SCM
 375 scm_body (void *d)
 376 {
 377   struct scm_data *data = (struct scm_data *)d;
 378   return scm_call_0 (data->proc);
 379 }
 380
 381 static SCM
 382 scm_handler (void *d, SCM tag, SCM args)
 383 {
 384   return SCM_BOOL_F;
 385 }
 386
 387 SCM_DEFINE (scm_with_continuation_barrier, "with-continuation-barrier", 1,0,0,
 388             (SCM proc),
 389 "Call @var{proc} and return its result.  Do not allow the invocation of\n"
 390 "continuations that would leave or enter the dynamic extent of the call\n"
 391 "to @code{with-continuation-barrier}.  Such an attempt causes an error\n"
 392 "to be signaled.\n"
 393 "\n"
 394 "Throws (such as errors) that are not caught from within @var{proc} are\n"
 395 "caught by @code{with-continuation-barrier}.  In that case, a short\n"
 396 "message is printed to the current error port and @code{#f} is returned.\n"
 397 "\n"
 398 "Thus, @code{with-continuation-barrier} returns exactly once.\n")
 399 #define FUNC_NAME s_scm_with_continuation_barrier
 400 {
 401   struct scm_data scm_data;
 402   scm_data.proc = proc;
 403   return scm_i_with_continuation_barrier (scm_body, &scm_data,
 404                                           scm_handler, &scm_data,
 405                                           scm_handle_by_message_noexit, NULL);
 406 }
 407 #undef FUNC_NAME
 408
 409 void
 410 scm_init_continuations ()
 411 {
 412   scm_tc16_continuation = scm_make_smob_type ("continuation", 0);
 413   scm_set_smob_mark (scm_tc16_continuation, continuation_mark);
 414   scm_set_smob_free (scm_tc16_continuation, continuation_free);
 415   scm_set_smob_print (scm_tc16_continuation, continuation_print);
 416   scm_set_smob_apply (scm_tc16_continuation, continuation_apply, 0, 0, 1);
 417 #include "libguile/continuations.x"
 418 }
 419
 420 /*
 421   Local Variables:
 422   c-file-style: "gnu"
 423   End:
 424 */