* Testsuite::
* Hints::
+* GDB Observers:: @value{GDBN} Currently available observers
* GNU Free Documentation License:: The license for this documentation
* Index::
@end menu
unavailable in many platforms.
@end enumerate
+@section Observing changes in @value{GDBN} internals
+@cindex observer pattern interface
+@cindex notifications about changes in internals
+
+In order to function properly, several modules need to be notified when
+some changes occur in the @value{GDBN} internals. Traditionally, these
+modules have relied on several paradigms, the most common ones being
+hooks and gdb-events. Unfortunately, none of these paradigms was
+versatile enough to become the standard notification mechanism in
+@value{GDBN}. The fact that they only supported one ``client'' was also
+a strong limitation.
+
+A new paradigm, based on the Observer pattern of the @cite{Design
+Patterns} book, has therefore been implemented. The goal was to provide
+a new interface overcoming the issues with the notification mechanisms
+previously available. This new interface needed to be strongly typed,
+easy to extend, and versatile enough to be used as the standard
+interface when adding new notifications.
+
+See @ref{GDB Observers} for a brief description of the observers
+currently implemented in GDB. The rationale for the current
+implementation is also briefly discussed.
+
@node User Interface
@chapter User Interface
@end table
+@include observer.texi
@include fdl.texi
@node Index
--- /dev/null
+@c -*-texinfo-*-
+@node GDB Observers
+@appendix @value{GDBN} Currently available observers
+
+@section Implementation rationale
+@cindex observers implementation rationale
+
+An @dfn{observer} is an entity which is interested in being notified
+when GDB reaches certain states, or certain events occur in GDB.
+The entity being observed is called the @dfn{subject}. To receive
+notifications, the observer attaches a callback to the subject.
+One subject can have several observers.
+
+@file{observer.c} implements an internal generic low-level event
+notification mechanism. This generic event notification mechansim is
+then re-used to implement the exported high-level notification
+management routines for all possible notifications.
+
+The current implementation of the generic observer provides support
+for contextual data. This contextual data is given to the subject
+when attaching the callback. In return, the subject will provide
+this contextual data back to the observer as a parameter of the
+callback.
+
+Note that the current support for the contextual data is only partial,
+as it lacks a mechanism that would deallocate this data when the
+callback is detached. This is not a problem so far, as this contextual
+data is only used internally to hold a function pointer. Later on, if
+a certain observer needs to provide support for user-level contextual
+data, then the generic notification mechanism will need need to be
+enhanced to allow the observer to provide a routine to deallocate the
+data when attaching the callback.
+
+The observer implementation is also currently not reentrant.
+In particular, it is therefore not possible to call the attach
+or detach routines during a notification.
+
+@section @code{normal_stop} Notifications
+@cindex @code{normal_stop} observer
+@cindex notification about inferior execution stop
+
+@value{GDBN} will notify all @code{normal_stop} observers when the
+inferior execution has just stopped, and all the associated internal
+processing (such as breakpoint commands, annotations, etc) is about to
+be performed before the @value{GDBN} prompt is returned to the user.
+
+The following interface is available to manage @code{normal_stop}
+observers:
+
+@deftypefun extern struct observer *observer_attach_normal_stop (observer_normal_stop_ftype *@var{f})
+Attach the given @code{normal_stop} callback function @var{f} and
+return the associated observer.
+@end deftypefun
+
+@deftypefun extern void observer_detach_normal_stop (struct observer *@var{observer});
+Remove @var{observer} from the list of observers to be notified when
+a @code{normal_stop} event occurs.
+@end deftypefun
+
+@deftypefun extern void observer_notify_normal_stop (void);
+Send a notification to all @code{normal_stop} observers.
+@end deftypefun
+
+
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