1 /* GDB Notifications to Observers.
2 Copyright 2003 Free Software Foundation, Inc.
4 This file is part of GDB.
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.
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.
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. */
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
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.
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
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.
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. */
56 /* The internal generic observer. */
58 typedef void (generic_observer_notification_ftype
) (const void *data
,
63 generic_observer_notification_ftype
*notify
;
64 /* No memory management needed for the following field for now. */
68 /* A list of observers, maintained by the subject. A subject is
69 actually represented by its list of observers. */
73 struct observer_list
*next
;
74 struct observer
*observer
;
77 /* Allocate a struct observer_list, intended to be used as a node
78 in the list of observers maintained by a subject. */
80 static struct observer_list
*
81 xalloc_observer_list_node (void)
83 struct observer_list
*node
= XMALLOC (struct observer_list
);
84 node
->observer
= XMALLOC (struct observer
);
88 /* The opposite of xalloc_observer_list_node, frees the memory for
92 xfree_observer_list_node (struct observer_list
*node
)
94 xfree (node
->observer
);
98 /* Attach the callback NOTIFY to a SUBJECT. The DATA is also stored,
99 in order for the subject to provide it back to the observer during
102 static struct observer
*
103 generic_observer_attach (struct observer_list
**subject
,
104 generic_observer_notification_ftype
* notify
,
107 struct observer_list
*observer_list
= xalloc_observer_list_node ();
109 observer_list
->next
= *subject
;
110 observer_list
->observer
->notify
= notify
;
111 observer_list
->observer
->data
= data
;
112 *subject
= observer_list
;
114 return observer_list
->observer
;
117 /* Remove the given OBSERVER from the SUBJECT. Once detached, OBSERVER
118 should no longer be used, as it is no longer valid. */
121 generic_observer_detach (struct observer_list
**subject
,
122 const struct observer
*observer
)
124 struct observer_list
*previous_node
= NULL
;
125 struct observer_list
*current_node
= *subject
;
127 while (current_node
!= NULL
)
129 if (current_node
->observer
== observer
)
131 if (previous_node
!= NULL
)
132 previous_node
->next
= current_node
->next
;
134 *subject
= current_node
->next
;
135 xfree_observer_list_node (current_node
);
138 previous_node
= current_node
;
139 current_node
= current_node
->next
;
142 /* We should never reach this point. However, this should not be
143 a very serious error, so simply report a warning to the user. */
144 warning ("Failed to detach observer");
147 /* Send a notification to all the observers of SUBJECT. ARGS is passed to
148 all observers as an argument to the notification callback. */
151 generic_observer_notify (struct observer_list
*subject
, const void *args
)
153 struct observer_list
*current_node
= subject
;
155 while (current_node
!= NULL
)
157 (*current_node
->observer
->notify
) (current_node
->observer
->data
, args
);
158 current_node
= current_node
->next
;
163 /* The following code is only used to unit-test the observers from our
164 testsuite. DO NOT USE IT within observer.c (or anywhere else for
167 /* If we define these variables and functions as `static', the
168 compiler will optimize them out. */
170 int observer_test_first_observer
= 0;
171 int observer_test_second_observer
= 0;
172 int observer_test_third_observer
= 0;
175 observer_test_first_notification_function (void)
177 observer_test_first_observer
++;
181 observer_test_second_notification_function (void)
183 observer_test_second_observer
++;
187 observer_test_third_notification_function (void)
189 observer_test_third_observer
++;
192 #include "observer.inc"