gdb/doc/observer.texi

   1 @c -*-texinfo-*-
   2 @node GDB Observers
   3 @appendix @value{GDBN} Currently available observers
   4
   5 @section Implementation rationale
   6 @cindex observers implementation rationale
   7
   8 An @dfn{observer} is an entity which is interested in being notified
   9 when GDB reaches certain states, or certain events occur in GDB.
  10 The entity being observed is called the @dfn{subject}.  To receive
  11 notifications, the observer attaches a callback to the subject.
  12 One subject can have several observers.
  13
  14 @file{observer.c} implements an internal generic low-level event
  15 notification mechanism.  This generic event notification mechanism is
  16 then re-used to implement the exported high-level notification
  17 management routines for all possible notifications.
  18
  19 The current implementation of the generic observer provides support
  20 for contextual data.  This contextual data is given to the subject
  21 when attaching the callback.  In return, the subject will provide
  22 this contextual data back to the observer as a parameter of the
  23 callback.
  24
  25 Note that the current support for the contextual data is only partial,
  26 as it lacks a mechanism that would deallocate this data when the
  27 callback is detached.  This is not a problem so far, as this contextual
  28 data is only used internally to hold a function pointer.  Later on, if
  29 a certain observer needs to provide support for user-level contextual
  30 data, then the generic notification mechanism will need to be
  31 enhanced to allow the observer to provide a routine to deallocate the
  32 data when attaching the callback.
  33
  34 The observer implementation is also currently not reentrant.
  35 In particular, it is therefore not possible to call the attach
  36 or detach routines during a notification.
  37
  38 @section @code{normal_stop} Notifications
  39 @cindex @code{normal_stop} observer
  40 @cindex notification about inferior execution stop
  41
  42 @value{GDBN} notifies all @code{normal_stop} observers when the
  43 inferior execution has just stopped, the associated messages and
  44 annotations have been printed, and the control is about to be returned
  45 to the user.
  46
  47 Note that the @code{normal_stop} notification is not emitted when
  48 the execution stops due to a breakpoint, and this breakpoint has
  49 a condition that is not met.  If the breakpoint has any associated
  50 commands list, the commands are executed after the notification
  51 is emitted.
  52
  53 The following interfaces are available to manage observers:
  54
  55 @deftypefun extern struct observer *observer_attach_@var{event} (observer_@var{event}_ftype *@var{f})
  56 Using the function @var{f}, create an observer that is notified when
  57 ever @var{event} occures, return the observer.
  58 @end deftypefun
  59
  60 @deftypefun extern void observer_detach_@var{event} (struct observer *@var{observer});
  61 Remove @var{observer} from the list of observers to be notified when
  62 @var{event} occurs.
  63 @end deftypefun
  64
  65 @deftypefun extern void observer_notify_@var{event} (void);
  66 Send a notification to all @var{event} observers.
  67 @end deftypefun
  68
  69 The following observable events are defined:
  70
  71 @c note: all events must take at least one parameter.
  72
  73 @deftypefun void normal_stop (struct bpstats *@var{bs})
  74 The inferior has stopped for real.
  75 @end deftypefun