libguile/continuations.c

   1 /* Copyright (C) 1995,1996,1998,2000,2001,2004 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_uintprint (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 ia64_getcontext (ucontext_t *) __asm__ ("getcontext");
 101 #endif /* __ia64__ */
 102
 103 /* this may return more than once: the first time with the escape
 104    procedure, then subsequently with the value to be passed to the
 105    continuation.  */
 106 #define FUNC_NAME "scm_make_continuation"
 107 SCM
 108 scm_make_continuation (int *first)
 109 {
 110   volatile SCM cont;
 111   scm_t_contregs *continuation;
 112   scm_t_contregs *rootcont = SCM_CONTREGS (scm_rootcont);
 113   long stack_size;
 114   SCM_STACKITEM * src;
 115 #ifdef __ia64__
 116   struct rv rv;
 117 #endif /* __ia64__ */
 118
 119   SCM_ENTER_A_SECTION;
 120   SCM_FLUSH_REGISTER_WINDOWS;
 121   stack_size = scm_stack_size (rootcont->base);
 122   continuation = scm_gc_malloc (sizeof (scm_t_contregs)
 123                                 + (stack_size - 1) * sizeof (SCM_STACKITEM),
 124                                 "continuation");
 125   continuation->num_stack_items = stack_size;
 126   continuation->dynenv = scm_dynwinds;
 127   continuation->throw_value = SCM_EOL;
 128   continuation->base = src = rootcont->base;
 129   continuation->seq = rootcont->seq;
 130   continuation->dframe = scm_last_debug_frame;
 131   SCM_NEWSMOB (cont, scm_tc16_continuation, continuation);
 132   SCM_EXIT_A_SECTION;
 133
 134 #if ! SCM_STACK_GROWS_UP
 135   src -= stack_size;
 136 #endif
 137   memcpy (continuation->stack, src, sizeof (SCM_STACKITEM) * stack_size);
 138
 139 #ifdef __ia64__
 140   rv = ia64_getcontext (&continuation->ctx);
 141   if (rv.first_return)
 142     {
 143       continuation->backing_store_size =
 144         continuation->ctx.uc_mcontext.sc_ar_bsp -
 145         (unsigned long) __libc_ia64_register_backing_store_base;
 146       continuation->backing_store = NULL;
 147       continuation->backing_store =
 148         scm_gc_malloc (continuation->backing_store_size,
 149                        "continuation backing store");
 150       memcpy (continuation->backing_store,
 151               (void *) __libc_ia64_register_backing_store_base,
 152               continuation->backing_store_size);
 153       *first = 1;
 154       return cont;
 155     }
 156   else
 157     {
 158       SCM ret = continuation->throw_value;
 159       *first = 0;
 160       continuation->throw_value = SCM_BOOL_F;
 161       return ret;
 162     }
 163 #else /* !__ia64__ */
 164   if (setjmp (continuation->jmpbuf))
 165     {
 166       SCM ret = continuation->throw_value;
 167       *first = 0;
 168       continuation->throw_value = SCM_BOOL_F;
 169       return ret;
 170     }
 171   else
 172     {
 173       *first = 1;
 174       return cont;
 175     }
 176 #endif /* !__ia64__ */
 177 }
 178 #undef FUNC_NAME
 179
 180
 181 /* Invoking a continuation proceeds as follows:
 182  *
 183  * - the stack is made large enough for the called continuation
 184  * - the old windchain is unwound down to the branching point
 185  * - the continuation stack is copied into place
 186  * - the windchain is rewound up to the continuation's context
 187  * - the continuation is invoked via longjmp (or setcontext)
 188  *
 189  * This order is important so that unwind and rewind handlers are run
 190  * with their correct stack.
 191  */
 192
 193 static void scm_dynthrow (SCM, SCM);
 194
 195 /* Grow the stack by a fixed amount to provide space to copy in the
 196  * continuation.  Possibly this function has to be called several times
 197  * recursively before enough space is available.  Make sure the compiler does
 198  * not optimize the growth array away by storing it's address into a global
 199  * variable.
 200  */
 201
 202 scm_t_bits scm_i_dummy;
 203
 204 static void
 205 grow_stack (SCM cont, SCM val)
 206 {
 207   scm_t_bits growth[100];
 208
 209   scm_i_dummy = (scm_t_bits) growth;
 210   scm_dynthrow (cont, val);
 211 }
 212
 213
 214 /* Copy the continuation stack into the current stack.  Calling functions from
 215  * within this function is safe, since only stack frames below this function's
 216  * own frame are overwritten.  Thus, memcpy can be used for best performance.
 217  */
 218
 219 typedef struct {
 220   scm_t_contregs *continuation;
 221   SCM_STACKITEM *dst;
 222 } copy_stack_data;
 223
 224 static void
 225 copy_stack (void *data)
 226 {
 227   copy_stack_data *d = (copy_stack_data *)data;
 228   memcpy (d->dst, d->continuation->stack,
 229           sizeof (SCM_STACKITEM) * d->continuation->num_stack_items);
 230 }
 231
 232 static void
 233 copy_stack_and_call (scm_t_contregs *continuation, SCM val,
 234                      SCM_STACKITEM * dst)
 235 {
 236   long delta;
 237   copy_stack_data data;
 238
 239   delta = scm_ilength (scm_dynwinds) - scm_ilength (continuation->dynenv);
 240   data.continuation = continuation;
 241   data.dst = dst;
 242   scm_i_dowinds (continuation->dynenv, delta, copy_stack, &data);
 243
 244   scm_last_debug_frame = continuation->dframe;
 245
 246   continuation->throw_value = val;
 247 #ifdef __ia64__
 248   memcpy ((void *) __libc_ia64_register_backing_store_base,
 249           continuation->backing_store,
 250           continuation->backing_store_size);
 251   setcontext (&continuation->ctx);
 252 #else
 253   longjmp (continuation->jmpbuf, 1);
 254 #endif
 255 }
 256
 257 /* Call grow_stack until the stack space is large enough, then, as the current
 258  * stack frame might get overwritten, let copy_stack_and_call perform the
 259  * actual copying and continuation calling.
 260  */
 261 static void
 262 scm_dynthrow (SCM cont, SCM val)
 263 {
 264   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 265   SCM_STACKITEM * dst = SCM_BASE (scm_rootcont);
 266   SCM_STACKITEM stack_top_element;
 267
 268 #if SCM_STACK_GROWS_UP
 269   if (dst + continuation->num_stack_items >= &stack_top_element)
 270     grow_stack (cont, val);
 271 #else
 272   dst -= continuation->num_stack_items;
 273   if (dst <= &stack_top_element)
 274     grow_stack (cont, val);
 275 #endif /* def SCM_STACK_GROWS_UP */
 276
 277   SCM_FLUSH_REGISTER_WINDOWS;
 278   copy_stack_and_call (continuation, val, dst);
 279 }
 280
 281
 282 static SCM
 283 continuation_apply (SCM cont, SCM args)
 284 #define FUNC_NAME "continuation_apply"
 285 {
 286   scm_t_contregs *continuation = SCM_CONTREGS (cont);
 287   scm_t_contregs *rootcont = SCM_CONTREGS (scm_rootcont);
 288
 289   if (continuation->seq != rootcont->seq
 290       /* this base comparison isn't needed */
 291       || continuation->base != rootcont->base)
 292     {
 293       SCM_MISC_ERROR ("continuation from wrong top level: ~S",
 294                       scm_list_1 (cont));
 295     }
 296
 297   scm_dynthrow (cont, scm_values (args));
 298   return SCM_UNSPECIFIED; /* not reached */
 299 }
 300 #undef FUNC_NAME
 301
 302
 303 void
 304 scm_init_continuations ()
 305 {
 306   scm_tc16_continuation = scm_make_smob_type ("continuation", 0);
 307   scm_set_smob_mark (scm_tc16_continuation, continuation_mark);
 308   scm_set_smob_free (scm_tc16_continuation, continuation_free);
 309   scm_set_smob_print (scm_tc16_continuation, continuation_print);
 310   scm_set_smob_apply (scm_tc16_continuation, continuation_apply, 0, 0, 1);
 311 #include "libguile/continuations.x"
 312 }
 313
 314 /*
 315   Local Variables:
 316   c-file-style: "gnu"
 317   End:
 318 */