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71 lines
2.9 KiB
Plaintext
71 lines
2.9 KiB
Plaintext
@c -*-texinfo-*-
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@node GDB Observers
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@appendix @value{GDBN} Currently available observers
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@section Implementation rationale
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@cindex observers implementation rationale
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An @dfn{observer} is an entity which is interested in being notified
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when GDB reaches certain states, or certain events occur in GDB.
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The entity being observed is called the @dfn{subject}. To receive
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notifications, the observer attaches a callback to the subject.
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One subject can have several observers.
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@file{observer.c} implements an internal generic low-level event
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notification mechanism. This generic event notification mechanism is
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then re-used to implement the exported high-level notification
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management routines for all possible notifications.
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The current implementation of the generic observer provides support
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for contextual data. This contextual data is given to the subject
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when attaching the callback. In return, the subject will provide
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this contextual data back to the observer as a parameter of the
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callback.
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Note that the current support for the contextual data is only partial,
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as it lacks a mechanism that would deallocate this data when the
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callback is detached. This is not a problem so far, as this contextual
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data is only used internally to hold a function pointer. Later on, if
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a certain observer needs to provide support for user-level contextual
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data, then the generic notification mechanism will need to be
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enhanced to allow the observer to provide a routine to deallocate the
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data when attaching the callback.
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The observer implementation is also currently not reentrant.
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In particular, it is therefore not possible to call the attach
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or detach routines during a notification.
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@section @code{normal_stop} Notifications
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@cindex @code{normal_stop} observer
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@cindex notification about inferior execution stop
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@value{GDBN} notifies all @code{normal_stop} observers when the
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inferior execution has just stopped, the associated messages and
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annotations have been printed, and the control is about to be returned
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to the user.
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Note that the @code{normal_stop} notification is not emitted when
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the execution stops due to a breakpoint, and this breakpoint has
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a condition that is not met. If the breakpoint has any associated
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commands list, the commands are executed after the notification
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is emitted.
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The following interface is available to manage @code{normal_stop}
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observers:
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@deftypefun extern struct observer *observer_attach_normal_stop (observer_normal_stop_ftype *@var{f})
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Attach the given @code{normal_stop} callback function @var{f} and
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return the associated observer.
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@end deftypefun
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@deftypefun extern void observer_detach_normal_stop (struct observer *@var{observer});
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Remove @var{observer} from the list of observers to be notified when
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a @code{normal_stop} event occurs.
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@end deftypefun
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@deftypefun extern void observer_notify_normal_stop (void);
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Send a notification to all @code{normal_stop} observers.
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@end deftypefun
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