| 1 | /* GDB Notifications to Observers. |
| 2 | |
| 3 | Copyright (C) 2003, 2004, 2007, 2008, 2009 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 3 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, see <http://www.gnu.org/licenses/>. */ |
| 19 | |
| 20 | /* An observer is an entity who is interested in being notified when GDB |
| 21 | reaches certain states, or certain events occur in GDB. The entity being |
| 22 | observed is called the Subject. To receive notifications, the observer |
| 23 | attaches a callback to the subject. One subject can have several |
| 24 | observers. |
| 25 | |
| 26 | This file implements an internal generic low-level event notification |
| 27 | mechanism based on the Observer paradigm described in the book "Design |
| 28 | Patterns". This generic event notification mechansim is then re-used |
| 29 | to implement the exported high-level notification management routines |
| 30 | for all possible notifications. |
| 31 | |
| 32 | The current implementation of the generic observer provides support |
| 33 | for contextual data. This contextual data is given to the subject |
| 34 | when attaching the callback. In return, the subject will provide |
| 35 | this contextual data back to the observer as a parameter of the |
| 36 | callback. |
| 37 | |
| 38 | FIXME: The current support for the contextual data is only partial, |
| 39 | as it lacks a mechanism that would deallocate this data when the |
| 40 | callback is detached. This is not a problem so far, as this contextual |
| 41 | data is only used internally to hold a function pointer. Later on, |
| 42 | if a certain observer needs to provide support for user-level |
| 43 | contextual data, then the generic notification mechanism will need |
| 44 | need to be enhanced to allow the observer to provide a routine to |
| 45 | deallocate the data when attaching the callback. |
| 46 | |
| 47 | This file is currently maintained by hand, but the long term plan |
| 48 | if the number of different notifications starts growing is to create |
| 49 | a new script (observer.sh) that would generate this file, and the |
| 50 | associated documentation. */ |
| 51 | |
| 52 | #include "defs.h" |
| 53 | #include "observer.h" |
| 54 | #include "command.h" |
| 55 | #include "gdbcmd.h" |
| 56 | |
| 57 | static int observer_debug; |
| 58 | static void |
| 59 | show_observer_debug (struct ui_file *file, int from_tty, |
| 60 | struct cmd_list_element *c, const char *value) |
| 61 | { |
| 62 | fprintf_filtered (file, _("Observer debugging is %s.\n"), value); |
| 63 | } |
| 64 | |
| 65 | /* The internal generic observer. */ |
| 66 | |
| 67 | typedef void (generic_observer_notification_ftype) (const void *data, |
| 68 | const void *args); |
| 69 | |
| 70 | struct observer |
| 71 | { |
| 72 | generic_observer_notification_ftype *notify; |
| 73 | /* No memory management needed for the following field for now. */ |
| 74 | void *data; |
| 75 | }; |
| 76 | |
| 77 | /* A list of observers, maintained by the subject. A subject is |
| 78 | actually represented by its list of observers. */ |
| 79 | |
| 80 | struct observer_list |
| 81 | { |
| 82 | struct observer_list *next; |
| 83 | struct observer *observer; |
| 84 | }; |
| 85 | |
| 86 | /* Allocate a struct observer_list, intended to be used as a node |
| 87 | in the list of observers maintained by a subject. */ |
| 88 | |
| 89 | static struct observer_list * |
| 90 | xalloc_observer_list_node (void) |
| 91 | { |
| 92 | struct observer_list *node = XMALLOC (struct observer_list); |
| 93 | node->observer = XMALLOC (struct observer); |
| 94 | return node; |
| 95 | } |
| 96 | |
| 97 | /* The opposite of xalloc_observer_list_node, frees the memory for |
| 98 | the given node. */ |
| 99 | |
| 100 | static void |
| 101 | xfree_observer_list_node (struct observer_list *node) |
| 102 | { |
| 103 | xfree (node->observer); |
| 104 | xfree (node); |
| 105 | } |
| 106 | |
| 107 | /* Attach the callback NOTIFY to a SUBJECT. The DATA is also stored, |
| 108 | in order for the subject to provide it back to the observer during |
| 109 | a notification. */ |
| 110 | |
| 111 | static struct observer * |
| 112 | generic_observer_attach (struct observer_list **subject, |
| 113 | generic_observer_notification_ftype * notify, |
| 114 | void *data) |
| 115 | { |
| 116 | struct observer_list *observer_list = xalloc_observer_list_node (); |
| 117 | |
| 118 | observer_list->next = *subject; |
| 119 | observer_list->observer->notify = notify; |
| 120 | observer_list->observer->data = data; |
| 121 | *subject = observer_list; |
| 122 | |
| 123 | return observer_list->observer; |
| 124 | } |
| 125 | |
| 126 | /* Remove the given OBSERVER from the SUBJECT. Once detached, OBSERVER |
| 127 | should no longer be used, as it is no longer valid. */ |
| 128 | |
| 129 | static void |
| 130 | generic_observer_detach (struct observer_list **subject, |
| 131 | const struct observer *observer) |
| 132 | { |
| 133 | struct observer_list *previous_node = NULL; |
| 134 | struct observer_list *current_node = *subject; |
| 135 | |
| 136 | while (current_node != NULL) |
| 137 | { |
| 138 | if (current_node->observer == observer) |
| 139 | { |
| 140 | if (previous_node != NULL) |
| 141 | previous_node->next = current_node->next; |
| 142 | else |
| 143 | *subject = current_node->next; |
| 144 | xfree_observer_list_node (current_node); |
| 145 | return; |
| 146 | } |
| 147 | previous_node = current_node; |
| 148 | current_node = current_node->next; |
| 149 | } |
| 150 | |
| 151 | /* We should never reach this point. However, this should not be |
| 152 | a very serious error, so simply report a warning to the user. */ |
| 153 | warning (_("Failed to detach observer")); |
| 154 | } |
| 155 | |
| 156 | /* Send a notification to all the observers of SUBJECT. ARGS is passed to |
| 157 | all observers as an argument to the notification callback. */ |
| 158 | |
| 159 | static void |
| 160 | generic_observer_notify (struct observer_list *subject, const void *args) |
| 161 | { |
| 162 | struct observer_list *current_node = subject; |
| 163 | |
| 164 | while (current_node != NULL) |
| 165 | { |
| 166 | (*current_node->observer->notify) (current_node->observer->data, args); |
| 167 | current_node = current_node->next; |
| 168 | } |
| 169 | } |
| 170 | |
| 171 | |
| 172 | /* The following code is only used to unit-test the observers from our |
| 173 | testsuite. DO NOT USE IT within observer.c (or anywhere else for |
| 174 | that matter)! */ |
| 175 | |
| 176 | /* If we define these variables and functions as `static', the |
| 177 | compiler will optimize them out. */ |
| 178 | |
| 179 | int observer_test_first_observer = 0; |
| 180 | int observer_test_second_observer = 0; |
| 181 | int observer_test_third_observer = 0; |
| 182 | |
| 183 | void |
| 184 | observer_test_first_notification_function (struct bpstats *bs) |
| 185 | { |
| 186 | observer_test_first_observer++; |
| 187 | } |
| 188 | |
| 189 | void |
| 190 | observer_test_second_notification_function (struct bpstats *bs) |
| 191 | { |
| 192 | observer_test_second_observer++; |
| 193 | } |
| 194 | |
| 195 | void |
| 196 | observer_test_third_notification_function (struct bpstats *bs) |
| 197 | { |
| 198 | observer_test_third_observer++; |
| 199 | } |
| 200 | |
| 201 | extern initialize_file_ftype _initialize_observer; /* -Wmissing-prototypes */ |
| 202 | |
| 203 | void |
| 204 | _initialize_observer (void) |
| 205 | { |
| 206 | add_setshow_zinteger_cmd ("observer", class_maintenance, |
| 207 | &observer_debug, _("\ |
| 208 | Set observer debugging."), _("\ |
| 209 | Show observer debugging."), _("\ |
| 210 | When non-zero, observer debugging is enabled."), |
| 211 | NULL, |
| 212 | show_observer_debug, |
| 213 | &setdebuglist, &showdebuglist); |
| 214 | } |
| 215 | |
| 216 | #include "observer.inc" |