libguile/root.c

   1 /* Copyright (C) 1995,1996,1997,1998,1999,2000, 2001, 2002, 2006, 2008 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 SCM scm_sys_protects[SCM_NUM_PROTECTS];
  42
  43 \f
  44
  45 /* {call-with-dynamic-root}
  46  *
  47  * Suspending the current thread to evaluate a thunk on the
  48  * same C stack but under a new root.
  49  *
  50  * Calls to call-with-dynamic-root return exactly once (unless
  51  * the process is somehow exitted).  */
  52
  53 /* cwdr fills out both of these structures, and then passes a pointer
  54    to them through scm_internal_catch to the cwdr_body and
  55    cwdr_handler functions, to tell them how to behave and to get
  56    information back from them.
  57
  58    A cwdr is a lot like a catch, except there is no tag (all
  59    exceptions are caught), and the body procedure takes the arguments
  60    passed to cwdr as A1 and ARGS.  The handler is also special since
  61    it is not directly run from scm_internal_catch.  It is executed
  62    outside the new dynamic root. */
  63
  64 struct cwdr_body_data {
  65   /* Arguments to pass to the cwdr body function.  */
  66   SCM a1, args;
  67
  68   /* Scheme procedure to use as body of cwdr.  */
  69   SCM body_proc;
  70 };
  71
  72 struct cwdr_handler_data {
  73   /* Do we need to run the handler? */
  74   int run_handler;
  75
  76   /* The tag and args to pass it. */
  77   SCM tag, args;
  78 };
  79
  80
  81 /* Invoke the body of a cwdr, assuming that the throw handler has
  82    already been set up.  DATA points to a struct set up by cwdr that
  83    says what proc to call, and what args to apply it to.
  84
  85    With a little thought, we could replace this with scm_body_thunk,
  86    but I don't want to mess with that at the moment.  */
  87 static SCM
  88 cwdr_body (void *data)
  89 {
  90   struct cwdr_body_data *c = (struct cwdr_body_data *) data;
  91
  92   return scm_apply (c->body_proc, c->a1, c->args);
  93 }
  94
  95 /* Record the fact that the body of the cwdr has thrown.  Record
  96    enough information to invoke the handler later when the dynamic
  97    root has been deestablished.  */
  98
  99 static SCM
 100 cwdr_handler (void *data, SCM tag, SCM args)
 101 {
 102   struct cwdr_handler_data *c = (struct cwdr_handler_data *) data;
 103
 104   c->run_handler = 1;
 105   c->tag = tag;
 106   c->args = args;
 107   return SCM_UNSPECIFIED;
 108 }
 109
 110 SCM
 111 scm_internal_cwdr (scm_t_catch_body body, void *body_data,
 112                    scm_t_catch_handler handler, void *handler_data,
 113                    SCM_STACKITEM *stack_start)
 114 {
 115   struct cwdr_handler_data my_handler_data;
 116   SCM answer, old_winds;
 117
 118   /* Exit caller's dynamic state.
 119    */
 120   old_winds = scm_i_dynwinds ();
 121   scm_dowinds (SCM_EOL, scm_ilength (old_winds));
 122
 123   scm_dynwind_begin (SCM_F_DYNWIND_REWINDABLE);
 124   scm_dynwind_current_dynamic_state (scm_make_dynamic_state (SCM_UNDEFINED));
 125
 126   my_handler_data.run_handler = 0;
 127   answer = scm_i_with_continuation_barrier (body, body_data,
 128                                             cwdr_handler, &my_handler_data,
 129                                             NULL, NULL);
 130
 131   scm_dynwind_end ();
 132
 133   /* Enter caller's dynamic state.
 134    */
 135   scm_dowinds (old_winds, - scm_ilength (old_winds));
 136
 137   /* Now run the real handler iff the body did a throw. */
 138   if (my_handler_data.run_handler)
 139     return handler (handler_data, my_handler_data.tag, my_handler_data.args);
 140   else
 141     return answer;
 142 }
 143
 144 /* The original CWDR for invoking Scheme code with a Scheme handler. */
 145
 146 static SCM
 147 cwdr (SCM proc, SCM a1, SCM args, SCM handler, SCM_STACKITEM *stack_start)
 148 {
 149   struct cwdr_body_data c;
 150
 151   c.a1 = a1;
 152   c.args = args;
 153   c.body_proc = proc;
 154
 155   return scm_internal_cwdr (cwdr_body, &c,
 156                             scm_handle_by_proc, &handler,
 157                             stack_start);
 158 }
 159
 160 SCM_DEFINE (scm_call_with_dynamic_root, "call-with-dynamic-root", 2, 0, 0,
 161            (SCM thunk, SCM handler),
 162             "Call @var{thunk} with a new dynamic state and within"
 163             "a continuation barrier.  The @var{handler} catches all"
 164             "otherwise uncaught throws and executes within the same"
 165             "dynamic context as @var{thunk}.")
 166 #define FUNC_NAME s_scm_call_with_dynamic_root
 167 {
 168   SCM_STACKITEM stack_place;
 169   return cwdr (thunk, SCM_EOL, SCM_EOL, handler, &stack_place);
 170 }
 171 #undef FUNC_NAME
 172
 173 SCM_DEFINE (scm_dynamic_root, "dynamic-root", 0, 0, 0,
 174            (),
 175             "Return an object representing the current dynamic root.\n\n"
 176             "These objects are only useful for comparison using @code{eq?}.\n")
 177 #define FUNC_NAME s_scm_dynamic_root
 178 {
 179   return SCM_I_CURRENT_THREAD->continuation_root;
 180 }
 181 #undef FUNC_NAME
 182
 183 SCM
 184 scm_apply_with_dynamic_root (SCM proc, SCM a1, SCM args, SCM handler)
 185 {
 186   SCM_STACKITEM stack_place;
 187   return cwdr (proc, a1, args, handler, &stack_place);
 188 }
 189
 190 \f
 191
 192 void
 193 scm_init_root ()
 194 {
 195 #include "libguile/root.x"
 196 }
 197
 198 /*
 199   Local Variables:
 200   c-file-style: "gnu"
 201   End:
 202 */