gdb/doc/observer.texi

   1 @c -*-texinfo-*-
   2
   3 @c This file is part of the GDB manual.
   4 @c
   5 @c Copyright (C) 2003, 2004, 2005, 2006
   6 @c               Free Software Foundation, Inc.
   7 @c
   8 @c See the file gdbint.texinfo for copying conditions.
   9 @c
  10 @c Also, the @deftypefun lines from this file are processed into a
  11 @c header file during the GDB build process.  Permission is granted
  12 @c to redistribute and/or modify those lines under the terms of the
  13 @c GNU General Public License as published by the Free Software
  14 @c Foundation; either version 2 of the License, or (at your option)
  15 @c any later version.
  16
  17 @node GDB Observers
  18 @appendix @value{GDBN} Currently available observers
  19
  20 @section Implementation rationale
  21 @cindex observers implementation rationale
  22
  23 An @dfn{observer} is an entity which is interested in being notified
  24 when GDB reaches certain states, or certain events occur in GDB.
  25 The entity being observed is called the @dfn{subject}.  To receive
  26 notifications, the observer attaches a callback to the subject.
  27 One subject can have several observers.
  28
  29 @file{observer.c} implements an internal generic low-level event
  30 notification mechanism.  This generic event notification mechanism is
  31 then re-used to implement the exported high-level notification
  32 management routines for all possible notifications.
  33
  34 The current implementation of the generic observer provides support
  35 for contextual data.  This contextual data is given to the subject
  36 when attaching the callback.  In return, the subject will provide
  37 this contextual data back to the observer as a parameter of the
  38 callback.
  39
  40 Note that the current support for the contextual data is only partial,
  41 as it lacks a mechanism that would deallocate this data when the
  42 callback is detached.  This is not a problem so far, as this contextual
  43 data is only used internally to hold a function pointer.  Later on, if
  44 a certain observer needs to provide support for user-level contextual
  45 data, then the generic notification mechanism will need to be
  46 enhanced to allow the observer to provide a routine to deallocate the
  47 data when attaching the callback.
  48
  49 The observer implementation is also currently not reentrant.
  50 In particular, it is therefore not possible to call the attach
  51 or detach routines during a notification.
  52
  53 @section Debugging
  54 Observer notifications can be traced using the command @samp{set debug
  55 observer 1} (@pxref{Debugging Output, , Optional messages about
  56 internal happenings, gdb, Debugging with @var{GDBN}}).
  57
  58 @section @code{normal_stop} Notifications
  59 @cindex @code{normal_stop} observer
  60 @cindex notification about inferior execution stop
  61
  62 @value{GDBN} notifies all @code{normal_stop} observers when the
  63 inferior execution has just stopped, the associated messages and
  64 annotations have been printed, and the control is about to be returned
  65 to the user.
  66
  67 Note that the @code{normal_stop} notification is not emitted when
  68 the execution stops due to a breakpoint, and this breakpoint has
  69 a condition that is not met.  If the breakpoint has any associated
  70 commands list, the commands are executed after the notification
  71 is emitted.
  72
  73 The following interfaces are available to manage observers:
  74
  75 @deftypefun extern struct observer *observer_attach_@var{event} (observer_@var{event}_ftype *@var{f})
  76 Using the function @var{f}, create an observer that is notified when
  77 ever @var{event} occurs, return the observer.
  78 @end deftypefun
  79
  80 @deftypefun extern void observer_detach_@var{event} (struct observer *@var{observer});
  81 Remove @var{observer} from the list of observers to be notified when
  82 @var{event} occurs.
  83 @end deftypefun
  84
  85 @deftypefun extern void observer_notify_@var{event} (void);
  86 Send a notification to all @var{event} observers.
  87 @end deftypefun
  88
  89 The following observable events are defined:
  90
  91 @deftypefun void normal_stop (struct bpstats *@var{bs})
  92 The inferior has stopped for real.
  93 @end deftypefun
  94
  95 @deftypefun void target_changed (struct target_ops *@var{target})
  96 The target's register contents have changed.
  97 @end deftypefun
  98
  99 @deftypefun void executable_changed (void)
 100 The executable being debugged by GDB has changed: The user decided
 101 to debug a different program, or the program he was debugging has
 102 been modified since being loaded by the debugger (by being recompiled,
 103 for instance).
 104 @end deftypefun
 105
 106 @deftypefun void inferior_created (struct target_ops *@var{objfile}, int @var{from_tty})
 107 @value{GDBN} has just connected to an inferior.  For @samp{run},
 108 @value{GDBN} calls this observer while the inferior is still stopped
 109 at the entry-point instruction.  For @samp{attach} and @samp{core},
 110 @value{GDBN} calls this observer immediately after connecting to the
 111 inferior, and before any information on the inferior has been printed.
 112 @end deftypefun
 113
 114 @deftypefun void solib_loaded (struct so_list *@var{solib})
 115 The shared library specified by @var{solib} has been loaded.  Note that
 116 when @value{GDBN} calls this observer, the library's symbols probably
 117 haven't been loaded yet.
 118 @end deftypefun
 119
 120 @deftypefun void solib_unloaded (struct so_list *@var{solib})
 121 The shared library specified by @var{solib} has been unloaded.
 122 @end deftypefun
 123
 124 @deftypefun void new_objfile (struct objfile *@var{objfile})
 125 The symbol file specified by @var{objfile} has been loaded.
 126 Called with @var{objfile} equal to @code{NULL} to indicate
 127 previously loaded symbol table data has now been invalidated.
 128 @end deftypefun
 129
 130 @deftypefun void new_thread (struct thread_info *@var{t})
 131 The thread specified by @var{t} has been created.
 132 @end deftypefun
 133
 134 @deftypefun void thread_exit (struct thread_info *@var{t})
 135 The thread specified by @var{t} has exited.
 136 @end deftypefun
 137
 138 @deftypefun void target_resumed (ptid_t @var{ptid})
 139 The target was resumed.  The @var{ptid} parameter specifies which
 140 thread was resume, and may be RESUME_ALL if all threads are resumed.
 141 @end deftypefun