Signals
A means for customization of object behaviour and a general purpose notification mechanism
The basic concept of the signal system is that of the emission
of a signal.
Signals are introduced per-type and are identified through strings.
Signals introduced for a parent type are available in derived types as well,
so basically they are a per-type facility that is inherited.
A signal emission mainly involves invocation of a certain set of callbacks in
precisely defined manner. There are two main categories of such callbacks,
per-object
Although signals can deal with any kind of instantiatable type,
i'm referring to those types as "object types" in the following, simply
because that is the context most users will encounter signals in.
ones and user provided ones.
The per-object callbacks are most often referred to as "object method
handler" or "default (signal) handler", while user provided callbacks are
usually just called "signal handler".
The object method handler is provided at signal creation time (this most
frequently happens at the end of an object class' creation), while user
provided handlers are frequently connected and disconnected to/from a certain
signal on certain object instances.
A signal emission consists of five stages, unless prematurely stopped:
1 - Invocation of the object method handler for %G_SIGNAL_RUN_FIRST signals
2 - Invocation of normal user-provided signal handlers (after flag %FALSE)
3 - Invocation of the object method handler for %G_SIGNAL_RUN_LAST signals
4 - Invocation of user provided signal handlers, connected with an after flag of %TRUE
5 - Invocation of the object method handler for %G_SIGNAL_RUN_CLEANUP signals
The user provided signal handlers are called in the order they were
connected in.
All handlers may prematurely stop a signal emission, and any number of
handlers may be connected, disconnected, blocked or unblocked during
a signal emission.
There are certain criteria for skipping user handlers in stages 2 and 4
of a signal emission.
First, user handlers may be blocked, blocked handlers are omitted
during callback invocation, to return from the "blocked" state, a
handler has to get unblocked exactly the same amount of times
it has been blocked before.
Second, upon emission of a %G_SIGNAL_DETAILED signal, an additional
"detail" argument passed in to g_signal_emit() has to match the detail
argument of the signal handler currently subject to invocation.
Specification of no detail argument for signal handlers (omission of the
detail part of the signal specification upon connection) serves as a
wildcard and matches any detail argument passed in to emission.
The #GSignalInvocationHint structure is used to pass on additional information
to callbacks during a signal emission.
@signal_id: The signal id of the signal invoking the callback
@detail: The detail passed on for this emission
@run_type: The stage the signal emission is currently in, this
field will contain one of %G_SIGNAL_RUN_FIRST,
%G_SIGNAL_RUN_LAST or %G_SIGNAL_RUN_CLEANUP.
The signal accumulator is a special callback function that can be used
to collect return values of the various callbacks that are called
during a signal emission. The signal accumulator is specified at signal
creation time, if it is left NULL, no accumulation of callback return
values is performed. The return value of signal emissions is then the
value returned by the last callback.
@ihint: Signal invocation hint, see #GSignalInvocationHint.
@return_accu: Accumulator to collect callback return values in, this
is the return value of the current signal emission.
@handler_return:
@data:
@Returns: The accumulator function returns whether the signal emission
should be aborted. Returning %FALSE means to abort the
current emission and %TRUE is returned for continuation.
@return_value: The return value of the most recent callback function.
This is the signature of marshaller functions, required to marshall
arrays of parameter values to signal emissions into C language callback
invocations. It is merely an alias to #GClosureMarshal since the #GClosure
mechanism takes over responsibility of actual function invocation for the
signal system.
A simple function pointer to get invoked when the signal is emitted. This
allows you tie a hook to the signal type, so that it will trap all emissions
of that signal, from any object.
You may not attach these to signals created with the #G_SIGNAL_NO_HOOKS flag.
@ihint: Signal invocation hint, see #GSignalInvocationHint.
@n_param_values: the number of parameters to the function, including
the instance on which the signal was emitted.
@param_values: the instance on which the signal was emitted, followed by the
parameters of the emission.
@data: user data associated with the hook.
@Returns: whether it wished to be removed. If it returns %TRUE, the signal
hook is disconnected (and destroyed).
The signal flags are used to specify a signal's behaviour, the overall
signal description outlines how especially the RUN flags control the
stages of a signal emission.
@G_SIGNAL_RUN_FIRST: Invoke the object method handler in the first emission stage.
@G_SIGNAL_RUN_LAST: Invoke the object method handler in the third emission stage.
@G_SIGNAL_RUN_CLEANUP: Invoke the object method handler in the last emission stage.
@G_SIGNAL_NO_RECURSE: Signals being emitted for an object while currently being in
emission for this very object will not be emitted recursively,
but instead cause the first emission to be restarted.
@G_SIGNAL_DETAILED: This signal supports "::detail" appendixes to the signal name
upon handler connections and emissions.
@G_SIGNAL_ACTION: Action signals are signals that may freely be emitted on alive
objects from user code via g_signal_emit() and friends, without
the need of being embedded into extra code that performs pre or
post emission adjustments on the object. They can also be thought
of as by third-party code generically callable object methods.
@G_SIGNAL_NO_HOOKS: No emissions hooks are supported for this signal.
@G_SIGNAL_MATCH_ID:
@G_SIGNAL_MATCH_DETAIL:
@G_SIGNAL_MATCH_CLOSURE:
@G_SIGNAL_MATCH_FUNC:
@G_SIGNAL_MATCH_DATA:
@G_SIGNAL_MATCH_UNBLOCKED:
A structure holding in-depth information for a specific signal. It is
filled in by the g_signal_query() function.
@signal_id: The signal id of the signal being queried, or 0 if the
signal to be queried was unknown.
@signal_name: The signal name.
@itype: The interface/instance type that this signal can be emitted for.
@signal_flags: The signal flags as passed in to g_signal_new().
@return_type: The return type for user callbacks.
@n_params: The number of parameters that user callbacks take.
@param_types: The individual parameter types for user callbacks, note that the
effective callback signature is:
@return_type callback (#gpointer data1,
[#param_types param_names,]
#gpointer data2);
@signal_name:
@itype:
@signal_flags:
@class_offset:
@accumulator:
@accu_data:
@c_marshaller:
@return_type:
@n_params:
@Varargs:
@Returns:
@signal_name:
@itype:
@signal_flags:
@class_closure:
@accumulator:
@accu_data:
@c_marshaller:
@return_type:
@n_params:
@param_types:
@Returns:
@signal_name:
@itype:
@signal_flags:
@class_closure:
@accumulator:
@accu_data:
@c_marshaller:
@return_type:
@n_params:
@args:
@Returns:
@signal_id:
@query:
@name:
@itype:
@Returns:
@signal_id:
@Returns:
@itype:
@n_ids:
@Returns:
@instance:
@signal_id:
@detail:
@Varargs:
@instance:
@detailed_signal:
@Varargs:
@instance_and_params:
@signal_id:
@detail:
@return_value:
@instance:
@signal_id:
@detail:
@var_args:
@instance:
@detailed_signal:
@c_handler:
@data:
@instance:
@detailed_signal:
@c_handler:
@data:
@instance:
@detailed_signal:
@c_handler:
@data:
@instance:
@detailed_signal:
@c_handler:
@gobject:
@connect_flags:
@Returns:
The connection flags are used to specify the behaviour of a signal's
connection.
@G_CONNECT_AFTER: whether the handler should be called before or after the
default handler of the signal.
@G_CONNECT_SWAPPED: whether the instance and data should be swapped when
calling the handler.
@instance:
@detailed_signal:
@c_handler:
@data:
@destroy_data:
@connect_flags:
@Returns:
@instance:
@detailed_signal:
@closure:
@after:
@Returns:
@instance:
@signal_id:
@detail:
@closure:
@after:
@Returns:
@instance:
@handler_id:
@instance:
@handler_id:
@instance:
@handler_id:
@instance:
@mask:
@signal_id:
@detail:
@closure:
@func:
@data:
@Returns:
@instance:
@mask:
@signal_id:
@detail:
@closure:
@func:
@data:
@Returns:
@instance:
@mask:
@signal_id:
@detail:
@closure:
@func:
@data:
@Returns:
@instance:
@mask:
@signal_id:
@detail:
@closure:
@func:
@data:
@Returns:
@instance:
@handler_id:
@Returns:
@instance:
@func:
@data:
@instance:
@func:
@data:
@instance:
@func:
@data:
@instance:
@signal_id:
@detail:
@may_be_blocked:
@Returns:
@instance:
@signal_id:
@detail:
@instance:
@detailed_signal:
@signal_id:
@instance_type:
@class_closure:
@instance_and_params:
@return_value:
@signal_id:
@detail:
@hook_func:
@hook_data:
@data_destroy:
@Returns:
@signal_id:
@hook_id:
@detailed_signal:
@itype:
@signal_id_p:
@detail_p:
@force_detail_quark:
@Returns:
@instance:
@Returns:
@itype:
@struct_offset:
@Returns: