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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 | |
6be67e67 | 15 | notification mechanism. This generic event notification mechanism is |
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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 | |
6be67e67 | 30 | data, then the generic notification mechanism will need to be |
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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 | ||
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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. | |
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52 | |
53 | The following interface is available to manage @code{normal_stop} | |
54 | observers: | |
55 | ||
56 | @deftypefun extern struct observer *observer_attach_normal_stop (observer_normal_stop_ftype *@var{f}) | |
57 | Attach the given @code{normal_stop} callback function @var{f} and | |
58 | return the associated observer. | |
59 | @end deftypefun | |
60 | ||
61 | @deftypefun extern void observer_detach_normal_stop (struct observer *@var{observer}); | |
62 | Remove @var{observer} from the list of observers to be notified when | |
63 | a @code{normal_stop} event occurs. | |
64 | @end deftypefun | |
65 | ||
66 | @deftypefun extern void observer_notify_normal_stop (void); | |
67 | Send a notification to all @code{normal_stop} observers. | |
68 | @end deftypefun | |
69 | ||
70 |