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
   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 #ifdef HAVE_CONFIG_H
  21 # include <config.h>
  22 #endif
  23
  24 #include <string.h>
  25 #include <stdio.h>
  26
  27 #include "libguile/_scm.h"
  28 #include "libguile/stackchk.h"
  29 #include "libguile/dynwind.h"
  30 #include "libguile/eval.h"
  31 #include "libguile/smob.h"
  32 #include "libguile/pairs.h"
  33 #include "libguile/throw.h"
  34 #include "libguile/fluids.h"
  35 #include "libguile/ports.h"
  36
  37 #include "libguile/root.h"
  38 \f
  39
  40 SCM scm_sys_protects[SCM_NUM_PROTECTS];
  41
  42 \f
  43
  44 /* {call-with-dynamic-root}
  45  *
  46  * Suspending the current thread to evaluate a thunk on the
  47  * same C stack but under a new root.
  48  *
  49  * Calls to call-with-dynamic-root return exactly once (unless
  50  * the process is somehow exitted).  */
  51
  52 /* cwdr fills out both of these structures, and then passes a pointer
  53    to them through scm_internal_catch to the cwdr_body and
  54    cwdr_handler functions, to tell them how to behave and to get
  55    information back from them.
  56
  57    A cwdr is a lot like a catch, except there is no tag (all
  58    exceptions are caught), and the body procedure takes the arguments
  59    passed to cwdr as A1 and ARGS.  The handler is also special since
  60    it is not directly run from scm_internal_catch.  It is executed
  61    outside the new dynamic root. */
  62
  63 struct cwdr_body_data {
  64   /* Arguments to pass to the cwdr body function.  */
  65   SCM a1, args;
  66
  67   /* Scheme procedure to use as body of cwdr.  */
  68   SCM body_proc;
  69 };
  70
  71 struct cwdr_handler_data {
  72   /* Do we need to run the handler? */
  73   int run_handler;
  74
  75   /* The tag and args to pass it. */
  76   SCM tag, args;
  77 };
  78
  79
  80 /* Invoke the body of a cwdr, assuming that the throw handler has
  81    already been set up.  DATA points to a struct set up by cwdr that
  82    says what proc to call, and what args to apply it to.
  83
  84    With a little thought, we could replace this with scm_body_thunk,
  85    but I don't want to mess with that at the moment.  */
  86 static SCM
  87 cwdr_body (void *data)
  88 {
  89   struct cwdr_body_data *c = (struct cwdr_body_data *) data;
  90
  91   return scm_apply (c->body_proc, c->a1, c->args);
  92 }
  93
  94 /* Record the fact that the body of the cwdr has thrown.  Record
  95    enough information to invoke the handler later when the dynamic
  96    root has been deestablished.  */
  97
  98 static SCM
  99 cwdr_handler (void *data, SCM tag, SCM args)
 100 {
 101   struct cwdr_handler_data *c = (struct cwdr_handler_data *) data;
 102
 103   c->run_handler = 1;
 104   c->tag = tag;
 105   c->args = args;
 106   return SCM_UNSPECIFIED;
 107 }
 108
 109 SCM
 110 scm_internal_cwdr (scm_t_catch_body body, void *body_data,
 111                    scm_t_catch_handler handler, void *handler_data,
 112                    SCM_STACKITEM *stack_start)
 113 {
 114   struct cwdr_handler_data my_handler_data;
 115   SCM answer, old_winds;
 116
 117   /* Exit caller's dynamic state.
 118    */
 119   old_winds = scm_i_dynwinds ();
 120   scm_dowinds (SCM_EOL, scm_ilength (old_winds));
 121
 122   scm_dynwind_begin (SCM_F_DYNWIND_REWINDABLE);
 123   scm_dynwind_current_dynamic_state (scm_make_dynamic_state (SCM_UNDEFINED));
 124
 125   my_handler_data.run_handler = 0;
 126   answer = scm_i_with_continuation_barrier (body, body_data,
 127                                             cwdr_handler, &my_handler_data,
 128                                             NULL, NULL);
 129
 130   scm_dynwind_end ();
 131
 132   /* Enter caller's dynamic state.
 133    */
 134   scm_dowinds (old_winds, - scm_ilength (old_winds));
 135
 136   /* Now run the real handler iff the body did a throw. */
 137   if (my_handler_data.run_handler)
 138     return handler (handler_data, my_handler_data.tag, my_handler_data.args);
 139   else
 140     return answer;
 141 }
 142
 143 /* The original CWDR for invoking Scheme code with a Scheme handler. */
 144
 145 static SCM
 146 cwdr (SCM proc, SCM a1, SCM args, SCM handler, SCM_STACKITEM *stack_start)
 147 {
 148   struct cwdr_body_data c;
 149
 150   c.a1 = a1;
 151   c.args = args;
 152   c.body_proc = proc;
 153
 154   return scm_internal_cwdr (cwdr_body, &c,
 155                             scm_handle_by_proc, &handler,
 156                             stack_start);
 157 }
 158
 159 SCM_DEFINE (scm_call_with_dynamic_root, "call-with-dynamic-root", 2, 0, 0,
 160            (SCM thunk, SCM handler),
 161             "Call @var{thunk} with a new dynamic state and within"
 162             "a continuation barrier.  The @var{handler} catches all"
 163             "otherwise uncaught throws and executes within the same"
 164             "dynamic context as @var{thunk}.")
 165 #define FUNC_NAME s_scm_call_with_dynamic_root
 166 {
 167   SCM_STACKITEM stack_place;
 168   return cwdr (thunk, SCM_EOL, SCM_EOL, handler, &stack_place);
 169 }
 170 #undef FUNC_NAME
 171
 172 SCM_DEFINE (scm_dynamic_root, "dynamic-root", 0, 0, 0,
 173            (),
 174             "Return an object representing the current dynamic root.\n\n"
 175             "These objects are only useful for comparison using @code{eq?}.\n")
 176 #define FUNC_NAME s_scm_dynamic_root
 177 {
 178   return SCM_I_CURRENT_THREAD->continuation_root;
 179 }
 180 #undef FUNC_NAME
 181
 182 SCM
 183 scm_apply_with_dynamic_root (SCM proc, SCM a1, SCM args, SCM handler)
 184 {
 185   SCM_STACKITEM stack_place;
 186   return cwdr (proc, a1, args, handler, &stack_place);
 187 }
 188
 189 \f
 190
 191 void
 192 scm_init_root ()
 193 {
 194 #include "libguile/root.x"
 195 }
 196
 197 /*
 198   Local Variables:
 199   c-file-style: "gnu"
 200   End:
 201 */