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@c -*-texinfo-*-

@c This file is part of the GDB manual.

@c

@c Copyright (C) 2003, 2004, 2005, 2006

@c               Free Software Foundation, Inc.

@c

@c See the file gdbint.texinfo for copying conditions.

@c

@c Also, the @deftypefun lines from this file are processed into a

@c header file during the GDB build process.  Permission is granted

@c to redistribute and/or modify those lines under the terms of the

@c GNU General Public License as published by the Free Software

@c Foundation; either version 2 of the License, or (at your option)

@c any later version.

@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 mechanism 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 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 Debugging

Observer notifications can be traced using the command @samp{set debug

observer 1} (@pxref{Debugging Output, , Optional messages about

internal happenings, gdb, Debugging with @var{GDBN}}).

@section @code{normal_stop} Notifications

@cindex @code{normal_stop} observer

@cindex notification about inferior execution stop

@value{GDBN} notifies all @code{normal_stop} observers when the

inferior execution has just stopped, the associated messages and

annotations have been printed, and the control is about to be returned

to the user.

Note that the @code{normal_stop} notification is not emitted when

the execution stops due to a breakpoint, and this breakpoint has

a condition that is not met.  If the breakpoint has any associated

commands list, the commands are executed after the notification

is emitted.

The following interfaces are available to manage observers:

@deftypefun extern struct observer *observer_attach_@var{event} (observer_@var{event}_ftype *@var{f})

Using the function @var{f}, create an observer that is notified when

ever @var{event} occurs, return the observer.

@end deftypefun

@deftypefun extern void observer_detach_@var{event} (struct observer *@var{observer});

Remove @var{observer} from the list of observers to be notified when

@var{event} occurs.

@end deftypefun

@deftypefun extern void observer_notify_@var{event} (void);

Send a notification to all @var{event} observers.

@end deftypefun

The following observable events are defined:

@c note: all events must take at least one parameter.

@deftypefun void normal_stop (struct bpstats *@var{bs})

The inferior has stopped for real.

@end deftypefun

@deftypefun void target_changed (struct target_ops *@var{target})

The target's register contents have changed.

@end deftypefun

@deftypefun void executable_changed (void *@var{unused_args})

The executable being debugged by GDB has changed: The user decided

to debug a different program, or the program he was debugging has

been modified since being loaded by the debugger (by being recompiled,

for instance).

@end deftypefun

@deftypefun void inferior_created (struct target_ops *@var{objfile}, int @var{from_tty})

@value{GDBN} has just connected to an inferior.  For @samp{run},

@value{GDBN} calls this observer while the inferior is still stopped

at the entry-point instruction.  For @samp{attach} and @samp{core},

@value{GDBN} calls this observer immediately after connecting to the

inferior, and before any information on the inferior has been printed.

@end deftypefun

@deftypefun void solib_loaded (struct so_list *@var{solib})

The shared library specified by @var{solib} has been loaded.  Note that

when @value{GDBN} calls this observer, the library's symbols probably

haven't been loaded yet.

@end deftypefun

@deftypefun void solib_unloaded (struct so_list *@var{solib})

The shared library specified by @var{solib} has been unloaded.

@end deftypefun

@deftypefun void new_objfile (struct objfile *@var{objfile})

The symbol file specified by @var{objfile} has been loaded.

Called with @var{objfile} equal to @code{NULL} to indicate

previously loaded symbol table data has now been invalidated.

@end deftypefun