libguile/root.c

   1 /* Copyright (C) 1995,1996,1997,1998,1999,2000, 2001, 2002, 2006, 2008, 2009 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 <string.h>
  26 #include <stdio.h>
  27
  28 #include "libguile/_scm.h"
  29 #include "libguile/stackchk.h"
  30 #include "libguile/dynwind.h"
  31 #include "libguile/eval.h"
  32 #include "libguile/smob.h"
  33 #include "libguile/pairs.h"
  34 #include "libguile/throw.h"
  35 #include "libguile/fluids.h"
  36 #include "libguile/ports.h"
  37
  38 #include "libguile/root.h"
  39 \f
  40
  41 /* {call-with-dynamic-root}
  42  *
  43  * Suspending the current thread to evaluate a thunk on the
  44  * same C stack but under a new root.
  45  *
  46  * Calls to call-with-dynamic-root return exactly once (unless
  47  * the process is somehow exitted).  */
  48
  49 /* cwdr fills out both of these structures, and then passes a pointer
  50    to them through scm_internal_catch to the cwdr_body and
  51    cwdr_handler functions, to tell them how to behave and to get
  52    information back from them.
  53
  54    A cwdr is a lot like a catch, except there is no tag (all
  55    exceptions are caught), and the body procedure takes the arguments
  56    passed to cwdr as A1 and ARGS.  The handler is also special since
  57    it is not directly run from scm_internal_catch.  It is executed
  58    outside the new dynamic root. */
  59
  60 struct cwdr_body_data {
  61   /* Arguments to pass to the cwdr body function.  */
  62   SCM a1, args;
  63
  64   /* Scheme procedure to use as body of cwdr.  */
  65   SCM body_proc;
  66 };
  67
  68 struct cwdr_handler_data {
  69   /* Do we need to run the handler? */
  70   int run_handler;
  71
  72   /* The tag and args to pass it. */
  73   SCM tag, args;
  74 };
  75
  76
  77 /* Invoke the body of a cwdr, assuming that the throw handler has
  78    already been set up.  DATA points to a struct set up by cwdr that
  79    says what proc to call, and what args to apply it to.
  80
  81    With a little thought, we could replace this with scm_body_thunk,
  82    but I don't want to mess with that at the moment.  */
  83 static SCM
  84 cwdr_body (void *data)
  85 {
  86   struct cwdr_body_data *c = (struct cwdr_body_data *) data;
  87
  88   return scm_apply (c->body_proc, c->a1, c->args);
  89 }
  90
  91 /* Record the fact that the body of the cwdr has thrown.  Record
  92    enough information to invoke the handler later when the dynamic
  93    root has been deestablished.  */
  94
  95 static SCM
  96 cwdr_handler (void *data, SCM tag, SCM args)
  97 {
  98   struct cwdr_handler_data *c = (struct cwdr_handler_data *) data;
  99
 100   c->run_handler = 1;
 101   c->tag = tag;
 102   c->args = args;
 103   return SCM_UNSPECIFIED;
 104 }
 105
 106 SCM
 107 scm_internal_cwdr (scm_t_catch_body body, void *body_data,
 108                    scm_t_catch_handler handler, void *handler_data,
 109                    SCM_STACKITEM *stack_start)
 110 {
 111   struct cwdr_handler_data my_handler_data;
 112   SCM answer, old_winds;
 113
 114   /* Exit caller's dynamic state.
 115    */
 116   old_winds = scm_i_dynwinds ();
 117   scm_dowinds (SCM_EOL, scm_ilength (old_winds));
 118
 119   scm_dynwind_begin (SCM_F_DYNWIND_REWINDABLE);
 120   scm_dynwind_current_dynamic_state (scm_make_dynamic_state (SCM_UNDEFINED));
 121
 122   my_handler_data.run_handler = 0;
 123   answer = scm_i_with_continuation_barrier (body, body_data,
 124                                             cwdr_handler, &my_handler_data,
 125                                             NULL, NULL);
 126
 127   scm_dynwind_end ();
 128
 129   /* Enter caller's dynamic state.
 130    */
 131   scm_dowinds (old_winds, - scm_ilength (old_winds));
 132
 133   /* Now run the real handler iff the body did a throw. */
 134   if (my_handler_data.run_handler)
 135     return handler (handler_data, my_handler_data.tag, my_handler_data.args);
 136   else
 137     return answer;
 138 }
 139
 140 /* The original CWDR for invoking Scheme code with a Scheme handler. */
 141
 142 static SCM
 143 cwdr (SCM proc, SCM a1, SCM args, SCM handler, SCM_STACKITEM *stack_start)
 144 {
 145   struct cwdr_body_data c;
 146
 147   c.a1 = a1;
 148   c.args = args;
 149   c.body_proc = proc;
 150
 151   return scm_internal_cwdr (cwdr_body, &c,
 152                             scm_handle_by_proc, &handler,
 153                             stack_start);
 154 }
 155
 156 SCM_DEFINE (scm_call_with_dynamic_root, "call-with-dynamic-root", 2, 0, 0,
 157            (SCM thunk, SCM handler),
 158             "Call @var{thunk} with a new dynamic state and within\n"
 159             "a continuation barrier.  The @var{handler} catches all\n"
 160             "otherwise uncaught throws and executes within the same\n"
 161             "dynamic context as @var{thunk}.")
 162 #define FUNC_NAME s_scm_call_with_dynamic_root
 163 {
 164   SCM_STACKITEM stack_place;
 165   return cwdr (thunk, SCM_EOL, SCM_EOL, handler, &stack_place);
 166 }
 167 #undef FUNC_NAME
 168
 169 SCM_DEFINE (scm_dynamic_root, "dynamic-root", 0, 0, 0,
 170            (),
 171             "Return an object representing the current dynamic root.\n\n"
 172             "These objects are only useful for comparison using @code{eq?}.\n")
 173 #define FUNC_NAME s_scm_dynamic_root
 174 {
 175   return SCM_I_CURRENT_THREAD->continuation_root;
 176 }
 177 #undef FUNC_NAME
 178
 179 SCM
 180 scm_apply_with_dynamic_root (SCM proc, SCM a1, SCM args, SCM handler)
 181 {
 182   SCM_STACKITEM stack_place;
 183   return cwdr (proc, a1, args, handler, &stack_place);
 184 }
 185
 186 \f
 187
 188 void
 189 scm_init_root ()
 190 {
 191 #include "libguile/root.x"
 192 }
 193
 194 /*
 195   Local Variables:
 196   c-file-style: "gnu"
 197   End:
 198 */