223 lines
6.8 KiB
C
223 lines
6.8 KiB
C
/* GDB Notifications to Observers.
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Copyright 2003 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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/* An observer is an entity who is interested in being notified when GDB
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reaches certain states, or certain events occur in GDB. The entity being
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observed is called the Subject. To receive notifications, the observer
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attaches a callback to the subject. One subject can have several
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observers.
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This file implements an internal generic low-level event notification
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mechanism based on the Observer paradigm described in the book "Design
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Patterns". This generic event notification mechansim is then re-used
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to implement the exported high-level notification management routines
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for all possible notifications.
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The current implementation of the generic observer provides support
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for contextual data. This contextual data is given to the subject
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when attaching the callback. In return, the subject will provide
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this contextual data back to the observer as a parameter of the
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callback.
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FIXME: The current support for the contextual data is only partial,
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as it lacks a mechanism that would deallocate this data when the
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callback is detached. This is not a problem so far, as this contextual
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data is only used internally to hold a function pointer. Later on,
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if a certain observer needs to provide support for user-level
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contextual data, then the generic notification mechanism will need
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need to be enhanced to allow the observer to provide a routine to
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deallocate the data when attaching the callback.
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This file is currently maintained by hand, but the long term plan
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if the number of different notifications starts growing is to create
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a new script (observer.sh) that would generate this file, and the
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associated documentation. */
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#include "defs.h"
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#include "observer.h"
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/* The internal generic observer. */
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typedef void (generic_observer_notification_ftype) (const void *data,
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const void *args);
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struct observer
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{
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generic_observer_notification_ftype *notify;
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/* No memory management needed for the following field for now. */
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void *data;
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};
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/* A list of observers, maintained by the subject. A subject is
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actually represented by its list of observers. */
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struct observer_list
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{
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struct observer_list *next;
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struct observer *observer;
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};
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/* Allocate a struct observer_list, intended to be used as a node
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in the list of observers maintained by a subject. */
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static struct observer_list *
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xalloc_observer_list_node (void)
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{
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struct observer_list *node = XMALLOC (struct observer_list);
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node->observer = XMALLOC (struct observer);
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return node;
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}
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/* The opposite of xalloc_observer_list_node, frees the memory for
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the given node. */
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static void
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xfree_observer_list_node (struct observer_list *node)
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{
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xfree (node->observer);
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xfree (node);
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}
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/* Attach the callback NOTIFY to a SUBJECT. The DATA is also stored,
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in order for the subject to provide it back to the observer during
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a notification. */
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static struct observer *
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generic_observer_attach (struct observer_list **subject,
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generic_observer_notification_ftype * notify,
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void *data)
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{
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struct observer_list *observer_list = xalloc_observer_list_node ();
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observer_list->next = *subject;
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observer_list->observer->notify = notify;
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observer_list->observer->data = data;
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*subject = observer_list;
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return observer_list->observer;
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}
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/* Remove the given OBSERVER from the SUBJECT. Once detached, OBSERVER
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should no longer be used, as it is no longer valid. */
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static void
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generic_observer_detach (struct observer_list **subject,
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const struct observer *observer)
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{
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struct observer_list *previous_node = NULL;
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struct observer_list *current_node = *subject;
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while (current_node != NULL)
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{
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if (current_node->observer == observer)
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{
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if (previous_node != NULL)
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previous_node->next = current_node->next;
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else
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*subject = current_node->next;
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xfree_observer_list_node (current_node);
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return;
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}
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previous_node = current_node;
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current_node = current_node->next;
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}
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/* We should never reach this point. However, this should not be
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a very serious error, so simply report a warning to the user. */
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warning ("Failed to detach observer");
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}
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/* Send a notification to all the observers of SUBJECT. ARGS is passed to
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all observers as an argument to the notification callback. */
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static void
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generic_observer_notify (struct observer_list *subject, const void *args)
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{
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struct observer_list *current_node = subject;
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while (current_node != NULL)
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{
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(*current_node->observer->notify) (current_node->observer->data, args);
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current_node = current_node->next;
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}
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}
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/* normal_stop notifications. */
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static struct observer_list *normal_stop_subject = NULL;
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static void
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observer_normal_stop_notification_stub (const void *data,
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const void *unused_args)
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{
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observer_normal_stop_ftype *notify = (observer_normal_stop_ftype *) data;
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(*notify) ();
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}
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struct observer *
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observer_attach_normal_stop (observer_normal_stop_ftype *f)
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{
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return generic_observer_attach (&normal_stop_subject,
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&observer_normal_stop_notification_stub,
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(void *) f);
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}
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void
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observer_detach_normal_stop (struct observer *observer)
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{
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generic_observer_detach (&normal_stop_subject, observer);
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}
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void
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observer_notify_normal_stop (void)
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{
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generic_observer_notify (normal_stop_subject, NULL);
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}
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/* The following code is only used to unit-test the observers from
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our testsuite. DO NOT USE IT within observer.c! */
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/* Since this code will not be used within GDB, it will trigger
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a warning if we decide to compile with -Wunused-function.
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This is ok for now. (brobecker 2003-03-18) */
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static int observer_test_first_observer = 0;
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static int observer_test_second_observer = 0;
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static int observer_test_third_observer = 0;
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static void
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observer_test_first_notification_function (void)
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{
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observer_test_first_observer++;
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}
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static void
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observer_test_second_notification_function (void)
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{
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observer_test_second_observer++;
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}
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static void
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observer_test_third_notification_function (void)
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{
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observer_test_third_observer++;
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}
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