libguile/root.c

   1 /* Copyright (C) 1995,1996,1997,1998,1999,2000, 2001, 2002 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 <string.h>
  22 #include <stdio.h>
  23
  24 #include "libguile/_scm.h"
  25 #include "libguile/stackchk.h"
  26 #include "libguile/dynwind.h"
  27 #include "libguile/eval.h"
  28 #include "libguile/smob.h"
  29 #include "libguile/pairs.h"
  30 #include "libguile/throw.h"
  31 #include "libguile/fluids.h"
  32 #include "libguile/ports.h"
  33
  34 #include "libguile/root.h"
  35 \f
  36
  37 SCM scm_sys_protects[SCM_NUM_PROTECTS];
  38
  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
 126   scm_dynwind_end ();
 127
 128   /* Enter caller's dynamic state.
 129    */
 130   scm_dowinds (old_winds, - scm_ilength (old_winds));
 131
 132   /* Now run the real handler iff the body did a throw. */
 133   if (my_handler_data.run_handler)
 134     return handler (handler_data, my_handler_data.tag, my_handler_data.args);
 135   else
 136     return answer;
 137 }
 138
 139 /* The original CWDR for invoking Scheme code with a Scheme handler. */
 140
 141 static SCM
 142 cwdr (SCM proc, SCM a1, SCM args, SCM handler, SCM_STACKITEM *stack_start)
 143 {
 144   struct cwdr_body_data c;
 145
 146   c.a1 = a1;
 147   c.args = args;
 148   c.body_proc = proc;
 149
 150   return scm_internal_cwdr (cwdr_body, &c,
 151                             scm_handle_by_proc, &handler,
 152                             stack_start);
 153 }
 154
 155 SCM_DEFINE (scm_call_with_dynamic_root, "call-with-dynamic-root", 2, 0, 0,
 156            (SCM thunk, SCM handler),
 157             "Call @var{thunk} with a new dynamic state and within"
 158             "a continuation barrier.  The @var{handler} catches all"
 159             "otherwise uncaught throws and executes within the same"
 160             "dynamic context as @var{thunk}.")
 161 #define FUNC_NAME s_scm_call_with_dynamic_root
 162 {
 163   SCM_STACKITEM stack_place;
 164   return cwdr (thunk, SCM_EOL, SCM_EOL, handler, &stack_place);
 165 }
 166 #undef FUNC_NAME
 167
 168 SCM_DEFINE (scm_dynamic_root, "dynamic-root", 0, 0, 0,
 169            (),
 170             "Return an object representing the current dynamic root.\n\n"
 171             "These objects are only useful for comparison using @code{eq?}.\n")
 172 #define FUNC_NAME s_scm_dynamic_root
 173 {
 174   return SCM_I_CURRENT_THREAD->continuation_root;
 175 }
 176 #undef FUNC_NAME
 177
 178 SCM
 179 scm_apply_with_dynamic_root (SCM proc, SCM a1, SCM args, SCM handler)
 180 {
 181   SCM_STACKITEM stack_place;
 182   return cwdr (proc, a1, args, handler, &stack_place);
 183 }
 184
 185 \f
 186
 187 void
 188 scm_init_root ()
 189 {
 190 #include "libguile/root.x"
 191 }
 192
 193 /*
 194   Local Variables:
 195   c-file-style: "gnu"
 196   End:
 197 */