libguile/continuations.c

   1 /* Copyright (C) 1995,1996,1998,2000,2001 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  16  */
  17
  18
  19 \f
  20
  21 #include "libguile/_scm.h"
  22
  23 #include <string.h>
  24
  25 #include "libguile/debug.h"
  26 #include "libguile/root.h"
  27 #include "libguile/stackchk.h"
  28 #include "libguile/smob.h"
  29 #include "libguile/ports.h"
  30 #include "libguile/dynwind.h"
  31 #include "libguile/values.h"
  32
  33 #include "libguile/validate.h"
  34 #include "libguile/continuations.h"
  35
  36 \f
  37
  38 /* {Continuations}
  39  */
  40
  41 scm_t_bits scm_tc16_continuation;
  42
  43 static SCM
  44 continuation_mark (SCM obj)
  45 {
  46   scm_t_contregs *continuation = SCM_CONTREGS (obj);
  47
  48   scm_gc_mark (continuation->throw_value);
  49   scm_mark_locations (continuation->stack, continuation->num_stack_items);
  50 #ifdef __ia64__
  51   if (continuation->backing_store)
  52     scm_mark_locations (continuation->backing_store,
  53                         continuation->backing_store_size /
  54                         sizeof (SCM_STACKITEM));
  55 #endif /* __ia64__ */
  56   return continuation->dynenv;
  57 }
  58
  59 static size_t
  60 continuation_free (SCM obj)
  61 {
  62   scm_t_contregs *continuation = SCM_CONTREGS (obj);
  63   /* stack array size is 1 if num_stack_items is 0 (rootcont).  */
  64   size_t extra_items = (continuation->num_stack_items > 0)
  65     ? (continuation->num_stack_items - 1)
  66     : 0;
  67   size_t bytes_free = sizeof (scm_t_contregs)
  68     + extra_items * sizeof (SCM_STACKITEM);
  69
  70 #ifdef __ia64__
  71   scm_gc_free (continuation->backing_store, continuation->backing_store_size,
  72                "continuation backing store");
  73 #endif /* __ia64__ */
  74   scm_gc_free (continuation, bytes_free, "continuation");
  75   return 0;
  76 }
  77
  78 static int
  79 continuation_print (SCM obj, SCM port, scm_print_state *state SCM_UNUSED)
  80 {
  81   scm_t_contregs *continuation = SCM_CONTREGS (obj);
  82
  83   scm_puts ("#<continuation ", port);
  84   scm_intprint (continuation->num_stack_items, 10, port);
  85   scm_puts (" @ ", port);
  86   scm_intprint (SCM_CELL_WORD_1 (obj), 16, port);
  87   scm_putc ('>', port);
  88   return 1;
  89 }
  90
  91 #ifdef __ia64__
  92 /* Extern declaration of getcontext()/setcontext() in order to redefine
  93    getcontext() since on ia64-linux the second return value indicates whether
  94    it returned from getcontext() itself or by running setcontext(). */
  95 struct rv
  96 {
  97   long retval;
  98   long first_return;
  99 };
 100 extern struct rv getcontext (ucontext_t *);
 101 extern int setcontext (ucontext_t *);
 102 #endif /* __ia64__ */
 103
 104 /* this may return more than once: the first time with the escape
 105    procedure, then subsequently with the value to be passed to the
 106    continuation.  */
 107 #define FUNC_NAME "scm_make_continuation"
 108 SCM
 109 scm_make_continuation (int *first)
 110 {
 111   volatile SCM cont;
 112   scm_t_contregs *continuation;
 113   scm_t_contregs *rootcont = SCM_CONTREGS (scm_rootcont);
 114   long stack_size;
 115   SCM_STACKITEM * src;
 116 #ifdef __ia64__
 117   struct rv rv;
 118 #endif /* __ia64__ */
 119
 120   SCM_ENTER_A_SECTION;
 121   SCM_FLUSH_REGISTER_WINDOWS;
 122   stack_size = scm_stack_size (rootcont->base);
 123   continuation = scm_gc_malloc (sizeof (scm_t_contregs)
 124                                 + (stack_size - 1) * sizeof (SCM_STACKITEM),
 125                                 "continuation");
 126   continuation->num_stack_items = stack_size;
 127   continuation->dynenv = scm_dynwinds;
 128   continuation->throw_value = SCM_EOL;
 129   continuation->base = src = rootcont->base;
 130   continuation->seq = rootcont->seq;
 131   continuation->dframe = scm_last_debug_frame;
 132   SCM_NEWSMOB (cont, scm_tc16_continuation, continuation);
 133   SCM_EXIT_A_SECTION;
 134
 135 #if ! SCM_STACK_GROWS_UP
 136   src -= stack_size;
 137 #endif
 138   memcpy (continuation->stack, src, sizeof (SCM_STACKITEM) * stack_size);
 139
 140 #ifdef __ia64__
 141   rv = getcontext (&continuation->ctx);
 142   if (rv.first_return)
 143     {
 144       continuation->backing_store_size =
 145         continuation->ctx.uc_mcontext.sc_ar_bsp -
 146         (unsigned long) __libc_ia64_register_backing_store_base;
 147       continuation->backing_store = NULL;
 148       continuation->backing_store =
 149         scm_gc_malloc (continuation->backing_store_size,
 150                        "continuation backing store");
 151       memcpy (continuation->backing_store,
 152               (void *) __libc_ia64_register_backing_store_base,
 153               continuation->backing_store_size);
 154       *first = 1;
 155       return cont;
 156     }
 157   else
 158     {
 159       SCM ret = continuation->throw_value;
 160       *first = 0;
 161       continuation->throw_value = SCM_BOOL_F;
 162       return ret;
 163     }
 164 #else /* !__ia64__ */
 165   if (setjmp (continuation->jmpbuf))
 166     {
 167       SCM ret = continuation->throw_value;
 168       *first = 0;
 169       continuation->throw_value = SCM_BOOL_F;
 170       return ret;
 171     }
 172   else
 173     {
 174       *first = 1;
 175       return cont;
 176     }
 177 #endif /* !__ia64__ */
 178 }
 179 #undef FUNC_NAME
 180
 181 static void scm_dynthrow (SCM, SCM);
 182
 183 /* Grow the stack by a fixed amount to provide space to copy in the
 184  * continuation.  Possibly this function has to be called several times
 185  * recursively before enough space is available.  Make sure the compiler does
 186  * not optimize the growth array away by storing it's address into a global
 187  * variable.
 188  */
 189
 190 scm_t_bits scm_i_dummy;
 191
 192 static void
 193 grow_stack (SCM cont, SCM val)
 194 {
 195   scm_t_bits growth[100];
 196
 197   scm_i_dummy = (scm_t_bits) growth;
 198   scm_dynthrow (cont, val);
 199 }
 200
 201
 202 /* Copy the continuation stack into the current stack.  Calling functions from
 203  * within this function is safe, since only stack frames below this function's
 204  * own frame are overwritten.  Thus, memcpy can be used for best performance.
 205  */
 206 static void
 207 copy_stack_and_call (scm_t_contregs *continuation, SCM val,
 208                      SCM_STACKITEM * dst)
 209 {
 210   memcpy (dst, continuation->stack,
 211           sizeof (SCM_STACKITEM) * continuation->num_stack_items);
 212
 213   scm_last_debug_frame = continuation->dframe;
 214
 215   continuation->throw_value = val;
 216 #ifdef __ia64__
 217   memcpy ((void *) __libc_ia64_register_backing_store_base,
 218           continuation->backing_store,
 219           continuation->backing_store_size);
 220   setcontext (&continuation->ctx);
 221 #else
 222   longjmp (continuation->jmpbuf, 1);
 223 #endif
 224 }
 225
 226
 227 /* Call grow_stack until the stack space is large enough, then, as the current
 228  * stack frame might get overwritten, let copy_stack_and_call perform the
 229  * actual copying and continuation calling.
 230  */
 231 static void
 232 scm_dynthrow (SCM cont, SCM val)
 233 {
 234   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 235   SCM_STACKITEM * dst = SCM_BASE (scm_rootcont);
 236   SCM_STACKITEM stack_top_element;
 237
 238 #if SCM_STACK_GROWS_UP
 239   if (SCM_PTR_GE (dst + continuation->num_stack_items, &stack_top_element))
 240     grow_stack (cont, val);
 241 #else
 242   dst -= continuation->num_stack_items;
 243   if (dst <= &stack_top_element)
 244     grow_stack (cont, val);
 245 #endif /* def SCM_STACK_GROWS_UP */
 246
 247   SCM_FLUSH_REGISTER_WINDOWS;
 248   copy_stack_and_call (continuation, val, dst);
 249 }
 250
 251
 252 static SCM
 253 continuation_apply (SCM cont, SCM args)
 254 #define FUNC_NAME "continuation_apply"
 255 {
 256   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 257   scm_t_contregs *rootcont = SCM_CONTREGS (scm_rootcont);
 258
 259   if (continuation->seq != rootcont->seq
 260       /* this base comparison isn't needed */
 261       || continuation->base != rootcont->base)
 262     {
 263       SCM_MISC_ERROR ("continuation from wrong top level: ~S",
 264                       scm_list_1 (cont));
 265     }
 266
 267   scm_dowinds (continuation->dynenv,
 268                scm_ilength (scm_dynwinds)
 269                - scm_ilength (continuation->dynenv));
 270
 271   scm_dynthrow (cont, scm_values (args));
 272   return SCM_UNSPECIFIED; /* not reached */
 273 }
 274 #undef FUNC_NAME
 275
 276
 277 void
 278 scm_init_continuations ()
 279 {
 280   scm_tc16_continuation = scm_make_smob_type ("continuation", 0);
 281   scm_set_smob_mark (scm_tc16_continuation, continuation_mark);
 282   scm_set_smob_free (scm_tc16_continuation, continuation_free);
 283   scm_set_smob_print (scm_tc16_continuation, continuation_print);
 284   scm_set_smob_apply (scm_tc16_continuation, continuation_apply, 0, 0, 1);
 285 #include "libguile/continuations.x"
 286 }
 287
 288 /*
 289   Local Variables:
 290   c-file-style: "gnu"
 291   End:
 292 */