1 /* GDB Notifications to Observers. 2 3 Copyright 2003, 2004 Free Software Foundation, Inc. 4 5 This file is part of GDB. 6 7 This program is free software; you can redistribute it and/or modify 8 it under the terms of the GNU General Public License as published by 9 the Free Software Foundation; either version 2 of the License, or 10 (at your option) any later version. 11 12 This program is distributed in the hope that it will be useful, 13 but WITHOUT ANY WARRANTY; without even the implied warranty of 14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 GNU General Public License for more details. 16 17 You should have received a copy of the GNU General Public License 18 along with this program; if not, write to the Free Software 19 Foundation, Inc., 59 Temple Place - Suite 330, 20 Boston, MA 02111-1307, USA. */ 21 22 /* An observer is an entity who is interested in being notified when GDB 23 reaches certain states, or certain events occur in GDB. The entity being 24 observed is called the Subject. To receive notifications, the observer 25 attaches a callback to the subject. One subject can have several 26 observers. 27 28 This file implements an internal generic low-level event notification 29 mechanism based on the Observer paradigm described in the book "Design 30 Patterns". This generic event notification mechansim is then re-used 31 to implement the exported high-level notification management routines 32 for all possible notifications. 33 34 The current implementation of the generic observer provides support 35 for contextual data. This contextual data is given to the subject 36 when attaching the callback. In return, the subject will provide 37 this contextual data back to the observer as a parameter of the 38 callback. 39 40 FIXME: The current support for the contextual data is only partial, 41 as it lacks a mechanism that would deallocate this data when the 42 callback is detached. This is not a problem so far, as this contextual 43 data is only used internally to hold a function pointer. Later on, 44 if a certain observer needs to provide support for user-level 45 contextual data, then the generic notification mechanism will need 46 need to be enhanced to allow the observer to provide a routine to 47 deallocate the data when attaching the callback. 48 49 This file is currently maintained by hand, but the long term plan 50 if the number of different notifications starts growing is to create 51 a new script (observer.sh) that would generate this file, and the 52 associated documentation. */ 53 54 #include "defs.h" 55 #include "observer.h" 56 #include "command.h" 57 #include "gdbcmd.h" 58 59 static int observer_debug; 60 61 /* The internal generic observer. */ 62 63 typedef void (generic_observer_notification_ftype) (const void *data, 64 const void *args); 65 66 struct observer 67 { 68 generic_observer_notification_ftype *notify; 69 /* No memory management needed for the following field for now. */ 70 void *data; 71 }; 72 73 /* A list of observers, maintained by the subject. A subject is 74 actually represented by its list of observers. */ 75 76 struct observer_list 77 { 78 struct observer_list *next; 79 struct observer *observer; 80 }; 81 82 /* Allocate a struct observer_list, intended to be used as a node 83 in the list of observers maintained by a subject. */ 84 85 static struct observer_list * 86 xalloc_observer_list_node (void) 87 { 88 struct observer_list *node = XMALLOC (struct observer_list); 89 node->observer = XMALLOC (struct observer); 90 return node; 91 } 92 93 /* The opposite of xalloc_observer_list_node, frees the memory for 94 the given node. */ 95 96 static void 97 xfree_observer_list_node (struct observer_list *node) 98 { 99 xfree (node->observer); 100 xfree (node); 101 } 102 103 /* Attach the callback NOTIFY to a SUBJECT. The DATA is also stored, 104 in order for the subject to provide it back to the observer during 105 a notification. */ 106 107 static struct observer * 108 generic_observer_attach (struct observer_list **subject, 109 generic_observer_notification_ftype * notify, 110 void *data) 111 { 112 struct observer_list *observer_list = xalloc_observer_list_node (); 113 114 observer_list->next = *subject; 115 observer_list->observer->notify = notify; 116 observer_list->observer->data = data; 117 *subject = observer_list; 118 119 return observer_list->observer; 120 } 121 122 /* Remove the given OBSERVER from the SUBJECT. Once detached, OBSERVER 123 should no longer be used, as it is no longer valid. */ 124 125 static void 126 generic_observer_detach (struct observer_list **subject, 127 const struct observer *observer) 128 { 129 struct observer_list *previous_node = NULL; 130 struct observer_list *current_node = *subject; 131 132 while (current_node != NULL) 133 { 134 if (current_node->observer == observer) 135 { 136 if (previous_node != NULL) 137 previous_node->next = current_node->next; 138 else 139 *subject = current_node->next; 140 xfree_observer_list_node (current_node); 141 return; 142 } 143 previous_node = current_node; 144 current_node = current_node->next; 145 } 146 147 /* We should never reach this point. However, this should not be 148 a very serious error, so simply report a warning to the user. */ 149 warning ("Failed to detach observer"); 150 } 151 152 /* Send a notification to all the observers of SUBJECT. ARGS is passed to 153 all observers as an argument to the notification callback. */ 154 155 static void 156 generic_observer_notify (struct observer_list *subject, const void *args) 157 { 158 struct observer_list *current_node = subject; 159 160 while (current_node != NULL) 161 { 162 (*current_node->observer->notify) (current_node->observer->data, args); 163 current_node = current_node->next; 164 } 165 } 166 167 168 /* The following code is only used to unit-test the observers from our 169 testsuite. DO NOT USE IT within observer.c (or anywhere else for 170 that matter)! */ 171 172 /* If we define these variables and functions as `static', the 173 compiler will optimize them out. */ 174 175 int observer_test_first_observer = 0; 176 int observer_test_second_observer = 0; 177 int observer_test_third_observer = 0; 178 179 void 180 observer_test_first_notification_function (struct bpstats *bs) 181 { 182 observer_test_first_observer++; 183 } 184 185 void 186 observer_test_second_notification_function (struct bpstats *bs) 187 { 188 observer_test_second_observer++; 189 } 190 191 void 192 observer_test_third_notification_function (struct bpstats *bs) 193 { 194 observer_test_third_observer++; 195 } 196 197 extern initialize_file_ftype _initialize_observer; /* -Wmissing-prototypes */ 198 199 void 200 _initialize_observer (void) 201 { 202 add_setshow_zinteger_cmd ("observer", class_maintenance, &observer_debug, "\ 203 Set observer debugging.", "\ 204 Show observer debugging.", "\ 205 When non-zero, observer debugging is enabled.", "\ 206 Observer debugging is %s.", 207 NULL, NULL, 208 &setdebuglist, &showdebuglist); 209 } 210 211 #include "observer.inc" 212