contrib/gdb-6.2.1/gdb/observer.c

   1 /* GDB Notifications to Observers.
   2    Copyright 2003 Free Software Foundation, Inc.
   3
   4    This file is part of GDB.
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 2 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program; if not, write to the Free Software
  18    Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 /* An observer is an entity who is interested in being notified when GDB
  22    reaches certain states, or certain events occur in GDB. The entity being
  23    observed is called the Subject. To receive notifications, the observer
  24    attaches a callback to the subject. One subject can have several
  25    observers.
  26
  27    This file implements an internal generic low-level event notification
  28    mechanism based on the Observer paradigm described in the book "Design
  29    Patterns".  This generic event notification mechansim is then re-used
  30    to implement the exported high-level notification management routines
  31    for all possible notifications.
  32
  33    The current implementation of the generic observer provides support
  34    for contextual data. This contextual data is given to the subject
  35    when attaching the callback. In return, the subject will provide
  36    this contextual data back to the observer as a parameter of the
  37    callback.
  38
  39    FIXME: The current support for the contextual data is only partial,
  40    as it lacks a mechanism that would deallocate this data when the
  41    callback is detached. This is not a problem so far, as this contextual
  42    data is only used internally to hold a function pointer. Later on,
  43    if a certain observer needs to provide support for user-level
  44    contextual data, then the generic notification mechanism will need
  45    need to be enhanced to allow the observer to provide a routine to
  46    deallocate the data when attaching the callback.
  47
  48    This file is currently maintained by hand, but the long term plan
  49    if the number of different notifications starts growing is to create
  50    a new script (observer.sh) that would generate this file, and the
  51    associated documentation.  */
  52
  53 #include "defs.h"
  54 #include "observer.h"
  55 #include "command.h"
  56 #include "gdbcmd.h"
  57
  58 static int observer_debug;
  59
  60 /* The internal generic observer.  */
  61
  62 typedef void (generic_observer_notification_ftype) (const void *data,
  63                                                     const void *args);
  64
  65 struct observer
  66 {
  67   generic_observer_notification_ftype *notify;
  68   /* No memory management needed for the following field for now.  */
  69   void *data;
  70 };
  71
  72 /* A list of observers, maintained by the subject.  A subject is
  73    actually represented by its list of observers.  */
  74
  75 struct observer_list
  76 {
  77   struct observer_list *next;
  78   struct observer *observer;
  79 };
  80
  81 /* Allocate a struct observer_list, intended to be used as a node
  82    in the list of observers maintained by a subject.  */
  83
  84 static struct observer_list *
  85 xalloc_observer_list_node (void)
  86 {
  87   struct observer_list *node = XMALLOC (struct observer_list);
  88   node->observer = XMALLOC (struct observer);
  89   return node;
  90 }
  91
  92 /* The opposite of xalloc_observer_list_node, frees the memory for
  93    the given node.  */
  94
  95 static void
  96 xfree_observer_list_node (struct observer_list *node)
  97 {
  98   xfree (node->observer);
  99   xfree (node);
 100 }
 101
 102 /* Attach the callback NOTIFY to a SUBJECT.  The DATA is also stored,
 103    in order for the subject to provide it back to the observer during
 104    a notification.  */
 105
 106 static struct observer *
 107 generic_observer_attach (struct observer_list **subject,
 108                          generic_observer_notification_ftype * notify,
 109                          void *data)
 110 {
 111   struct observer_list *observer_list = xalloc_observer_list_node ();
 112
 113   observer_list->next = *subject;
 114   observer_list->observer->notify = notify;
 115   observer_list->observer->data = data;
 116   *subject = observer_list;
 117
 118   return observer_list->observer;
 119 }
 120
 121 /* Remove the given OBSERVER from the SUBJECT.  Once detached, OBSERVER
 122    should no longer be used, as it is no longer valid.  */
 123
 124 static void
 125 generic_observer_detach (struct observer_list **subject,
 126                          const struct observer *observer)
 127 {
 128   struct observer_list *previous_node = NULL;
 129   struct observer_list *current_node = *subject;
 130
 131   while (current_node != NULL)
 132     {
 133       if (current_node->observer == observer)
 134         {
 135           if (previous_node != NULL)
 136             previous_node->next = current_node->next;
 137           else
 138             *subject = current_node->next;
 139           xfree_observer_list_node (current_node);
 140           return;
 141         }
 142       previous_node = current_node;
 143       current_node = current_node->next;
 144     }
 145
 146   /* We should never reach this point.  However, this should not be
 147      a very serious error, so simply report a warning to the user.  */
 148   warning ("Failed to detach observer");
 149 }
 150
 151 /* Send a notification to all the observers of SUBJECT.  ARGS is passed to
 152    all observers as an argument to the notification callback.  */
 153
 154 static void
 155 generic_observer_notify (struct observer_list *subject, const void *args)
 156 {
 157   struct observer_list *current_node = subject;
 158
 159   while (current_node != NULL)
 160     {
 161       (*current_node->observer->notify) (current_node->observer->data, args);
 162       current_node = current_node->next;
 163     }
 164 }
 165
 166
 167 /* The following code is only used to unit-test the observers from our
 168    testsuite.  DO NOT USE IT within observer.c (or anywhere else for
 169    that matter)!  */
 170
 171 /* If we define these variables and functions as `static', the
 172    compiler will optimize them out.  */
 173
 174 int observer_test_first_observer = 0;
 175 int observer_test_second_observer = 0;
 176 int observer_test_third_observer = 0;
 177
 178 void
 179 observer_test_first_notification_function (struct bpstats *bs)
 180 {
 181   observer_test_first_observer++;
 182 }
 183
 184 void
 185 observer_test_second_notification_function (struct bpstats *bs)
 186 {
 187   observer_test_second_observer++;
 188 }
 189
 190 void
 191 observer_test_third_notification_function (struct bpstats *bs)
 192 {
 193   observer_test_third_observer++;
 194 }
 195
 196 extern initialize_file_ftype _initialize_observer; /* -Wmissing-prototypes */
 197
 198 void
 199 _initialize_observer (void)
 200 {
 201   add_setshow_zinteger_cmd ("observer", class_maintenance, &observer_debug, "\
 202 Set observer debugging.\n\
 203 When non-zero, observer debugging is enabled.",  "\
 204 Show observer debugging.\n\
 205 When non-zero, observer debugging is enabled.",
 206                             NULL, NULL,
 207                             &setdebuglist, &showdebuglist);
 208 }
 209
 210 #include "observer.inc"