93 lines
3.8 KiB
Plaintext
93 lines
3.8 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 Debugging
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Observer notifications can be traced using the command @samp{set debug
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observer 1} (@pxref{Debugging Output, , Optional messages about
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internal happenings, gdb, Debugging with @var{GDBN}}).
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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 interfaces are available to manage observers:
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@deftypefun extern struct observer *observer_attach_@var{event} (observer_@var{event}_ftype *@var{f})
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Using the function @var{f}, create an observer that is notified when
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ever @var{event} occures, return the observer.
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@end deftypefun
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@deftypefun extern void observer_detach_@var{event} (struct observer *@var{observer});
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Remove @var{observer} from the list of observers to be notified when
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@var{event} occurs.
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@end deftypefun
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@deftypefun extern void observer_notify_@var{event} (void);
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Send a notification to all @var{event} observers.
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@end deftypefun
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The following observable events are defined:
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@c note: all events must take at least one parameter.
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@deftypefun void normal_stop (struct bpstats *@var{bs})
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The inferior has stopped for real.
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@end deftypefun
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@deftypefun void target_changed (struct target_ops *@var{target})
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The target's register contents have changed.
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@end deftypefun
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@deftypefun void inferior_created (struct target_ops *@var{objfile}, int @var{from_tty})
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@value{GDBN} has just connected to an inferior. For @samp{run},
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@value{GDBN} calls this observer while the inferior is still stopped
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at the entry-point instruction. For @samp{attach} and @samp{core},
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@value{GDBN} calls this observer immediately after connecting to the
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inferior, and before any information on the inferior has been printed.
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@end deftypefun
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