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Improvements from Owen's feedback.

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* gobject/tmpl/gclosure.sgml: Improvements from Owen's feedback.
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Matthias Clasen 2003-10-14 22:57:32 +00:00
parent 9d641fd17a
commit 4dd7b60fb9
2 changed files with 117 additions and 49 deletions
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docs/reference/ChangeLog
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@ -1,3 +1,7 @@
Wed Oct 15 00:56:30 2003 Matthias Clasen <maclas@gmx.de>
* gobject/tmpl/gclosure.sgml: Improvements from Owen's feedback.
Tue Oct 14 02:35:45 2003 Matthias Clasen <maclas@gmx.de>
* gobject/gobject-sections.txt: Move the g_cclosure_marshal_*

162
docs/reference/gobject/tmpl/gclosure.sgml
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@ -21,6 +21,40 @@ convert between #GValue<!-- -->s and suitable representations in the runtime
of the language in order to use functions written in that languages as
callbacks.
</para>
<para>
Within GObject, closures play an important role in the implementation of
signals. When a signal is registered, the @c_marshaller argument to
g_signal_new() specifies the default C marshaller for any closure which is
connected to this signal. GObject provides a number of C marshallers
for this purpose, see the g_cclosure_marshal_*() functions. Additional
C marshallers can be generated with the <link linkend="glib-genmarshal"
>glib-genmarshal</link> utility.
Closures can be explicitly connected to signals with
g_signal_connect_closure(), but it usually more convenient to let GObject
create a closure automatically by using one of the g_signal_connect_*()
functions which take a callback function/user data pair.
</para>
<para>
Using closures has a number of important advantages over a simple
callback function/data pointer combination:
<itemizedlist>
<listitem><para>
Closures allow the callee to get the types of the callback parameters,
which means that language bindings don't have to write individual glue
for each callback type.
</para></listitem>
<listitem><para>
The reference counting of #GClosure makes it easy to handle reentrancy
right; if a callback is removed while it is being invoked, the closure
and it's parameters won't be freed until the invocation finishes.
</para></listitem>
<listitem><para>
g_closure_invalidate() and invalidation notifiers allow callbacks to be
automatically removed when the objects they point to go away.
</para></listitem>
</itemizedlist>
</para>
<!-- ##### SECTION See_Also ##### -->
<para>
@ -130,34 +164,34 @@ on closures.
<!-- ##### FUNCTION g_cclosure_new ##### -->
<para>
Creates a new closure which invokes @callback_func with @user_data as last
parameter.
Creates a new closure which invokes @callback_func with @user_data as
the last parameter.
</para>
@callback_func: the function to invoke
@user_data: user data to pass to @callback_func
@destroy_data: destroy notify to be called when @user_data is destroyed
@destroy_data: destroy notify to be called when @user_data is no longer used
@Returns: a new #GCClosure
<!-- ##### FUNCTION g_cclosure_new_swap ##### -->
<para>
Creates a new closure which invokes @callback_func with @user_data as first
parameter.
Creates a new closure which invokes @callback_func with @user_data as
the first parameter.
</para>
@callback_func: the function to invoke
@user_data: user data to pass to @callback_func
@destroy_data: destroy notify to be called when @user_data is destroyed
@destroy_data: destroy notify to be called when @user_data is no longer used
@Returns: a new #GCClosure
<!-- ##### FUNCTION g_cclosure_new_object ##### -->
<para>
A variant of g_cclosure_new() which uses @object as @user_data
and calls g_object_watch_closure() on @object and the
created closure. This function is mainly useful when implementing new types
of closures.
A variant of g_cclosure_new() which uses @object as @user_data and calls
g_object_watch_closure() on @object and the created closure. This function
is useful when you have a callback closely associated with a #GObject,
and want the callback to no longer run after the object is is freed.
</para>
@callback_func: the function to invoke
@ -167,10 +201,10 @@ of closures.
<!-- ##### FUNCTION g_cclosure_new_object_swap ##### -->
<para>
A variant of g_cclosure_new_swap() which uses @object as @user_data
and calls g_object_watch_closure() on @object and the
created closure. This function is mainly useful when implementing new types
of closures.
A variant of g_cclosure_new_swap() which uses @object as @user_data and calls
g_object_watch_closure() on @object and the created closure. This function
is useful when you have a callback closely associated with a #GObject,
and want the callback to no longer run after the object is is freed.
</para>
@callback_func: the function to invoke
@ -206,10 +240,26 @@ alive while the caller holds a pointer to it.
<!-- ##### FUNCTION g_closure_sink ##### -->
<para>
Takes over the initial ownership of a closure.
When closures are newly created, they get an initial reference count
of 1, eventhough no caller has yet invoked g_closure_ref() on the @closure.
Code entities that store closures for notification purposes are supposed
to call this function, for example like this:
Each closure is initially created in a<firstterm>floating</firstterm> state,
which means that the initial reference count is not owned by any caller.
g_closure_sink() checks to see if the object is still floating, and if so,
unsets the floating state and decreases the reference count. If the closure
is not floating, g_closure_sink() does nothing. The reason for the existance
of the floating state is to prevent cumbersome code sequences like:
<programlisting>
closure = g_cclosure_new (cb_func, cb_data);
g_source_set_closure (source, closure);
g_closure_unref (closure); /* XXX GObject doesn't really need this */
</programlisting>
Because g_source_set_closure() (and similar functions) take ownership of the
initial reference count, if it is unowned, we instead can write:
<programlisting>
g_source_set_closure (source, g_cclosure_new (cb_func, cb_data));
</programlisting>
</para>
<para>
Generally, this function is used together with g_closure_ref(). Ane example
of storing a closure for later notification looks like:
<informalexample><programlisting>
static GClosure *notify_closure = NULL;
void
@ -225,6 +275,8 @@ foo_notify_set_closure (GClosure *closure)
}
}
</programlisting></informalexample>
</para>
<para>
Because g_closure_sink() may decrement the reference count of a closure
(if it hasn't been called on @closure yet) just like g_closure_unref(),
g_closure_ref() should be called prior to this function.
@ -236,10 +288,9 @@ g_closure_ref() should be called prior to this function.
<!-- ##### FUNCTION g_closure_unref ##### -->
<para>
Decrements the reference count of a closure after it was
previously incremented by the same caller. The closure
will most likely be destroyed and freed after this function
returns.
Decrements the reference count of a closure after it was previously
incremented by the same caller. If no other callers are using the closure,
then the closure will be destroyed and freed.
</para>
@closure: #GClosure to decrement the reference count on
@ -247,7 +298,7 @@ returns.
<!-- ##### FUNCTION g_closure_invoke ##### -->
<para>
Invokes the closure.
Invokes the closure, i.e. executes the callback represented by the @closure.
</para>
@closure: a #GClosure
@ -263,11 +314,16 @@ Invokes the closure.
<para>
Sets a flag on the closure to indicate that it's calling environment has
become invalid, and thus causes any future invocations of g_closure_invoke()
on this @closure to be ignored.
Also, invalidation notifiers installed on the closure will be called
at this point, and since invalidation notifiers may unreference
the closure, @closure should be considered an invalidated pointer
after this function, unless g_closure_ref() was called beforehand.
on this @closure to be ignored. Also, invalidation notifiers installed on
the closure will be called at this point. Note that unless you are holding
a reference to the closure yourself, the invalidation notifiers may unref
the closure and cause it to be destroyed, so if you need to access the
closure after calling g_closure_invalidate(), make sure that you've
previously called g_closure_ref().
</para>
<para>
Note that g_closure_invalidate() will also be called when the reference count
of a closure drops to zero (unless it has already been invalidated before).
</para>
@closure: GClosure to invalidate
@ -276,8 +332,11 @@ after this function, unless g_closure_ref() was called beforehand.
<!-- ##### FUNCTION g_closure_add_finalize_notifier ##### -->
<para>
Registers a finalization notifier which will be called when the reference
count of @closure goes down to 0. Finalization notifiers are invoked after
invalidation notifiers, in an unspecified order.
count of @closure goes down to 0. Multiple finalization notifiers on a
single closure are invoked in unspecified order. If a single call to
g_closure_unref() results in the closure being both invalidated and
finalized, then the invalidate notifiers will be run before the finalize
notifiers.
</para>
@closure: a #GClosure
@ -299,8 +358,8 @@ invoked before finalization notifiers, in an unspecified order.
<!-- ##### FUNCTION g_closure_remove_finalize_notifier ##### -->
<para>
Removes a finalization notifier. Notifiers may only be removed before or
during their invocation.
Removes a finalization notifier. Notifiers are automatically removed after
they are run.
</para>
@closure: a #GClosure
@ -311,8 +370,8 @@ during their invocation.
<!-- ##### FUNCTION g_closure_remove_invalidate_notifier ##### -->
<para>
Removes a invalidation notifier. Notifiers may only be removed before or
during their invocation.
Removes a invalidation notifier. Notifiers are automatically removed after
they are run.
</para>
@closure: a #GClosure
@ -371,10 +430,11 @@ MyClosure *my_closure_new (gpointer data)
<!-- ##### FUNCTION g_closure_set_marshal ##### -->
<para>
Sets the marshaller of @closure. A marshaller set with g_closure_set_marshal()
should interpret its @marshal_data argument as a callback function to be
invoked instead of @closure->callback, provided it is not %NULL. GObject provides a number of predefined marshallers for use with #GCClosure<!-- -->s,
see the g_cclosure_marshal_*() functions.
Sets the marshaller of @closure. The @marshal_data provides a way for a
meta marshaller to provide additional information to the marshaller.
(See g_closure_set_meta_marshal().) For GObject's C predefined marshallers
(the g_cclosure_marshal_*() functions), what it provides is a callback
function to use instead of @closure->callback.
</para>
@closure: a #GClosure
@ -384,8 +444,9 @@ see the g_cclosure_marshal_*() functions.
<!-- ##### FUNCTION g_closure_add_marshal_guards ##### -->
<para>
Adds a pair of notifiers which get invoked before and after the closure
callback, respectively. See g_object_watch_closure() for a use of marshal
guards.
callback, respectively. This is typically used to protect the extra arguments
for the duration of the callback. See g_object_watch_closure() for an
example of marshal guards.
</para>
@closure: a #GClosure
@ -397,17 +458,20 @@ guards.
<!-- ##### FUNCTION g_closure_set_meta_marshal ##### -->
<para>
Sets the meta marshaller of @closure. A meta marshaller
should use its @marshal_data argument together with @closure->data
to determine the callback function to use, and pass it as @marshal_data
to @closure->marshal.
Sets the meta marshaller of @closure.
A meta marshaller wraps @closure->marshal and modifies the way it is called
in some fashion. The most common use of this facility is for C callbacks.
The same marshallers (generated by
<link linkend="glib-genmarshal">glib-genmarshal</link>) are used everywhere,
but the way that we get the callback function differs. In most cases we want
to use @closure->callback, but in other cases we want to use use some
different technique to retrieve the callbakc function.
</para>
<para>
As an example for the use of a meta marshaller, consider a closure whose
@data member contains a pointer to a class structure. The meta marshaller
could then be given an offset into this struct in @marshal_data, and use
it to determine the class member function to use as callback. This is
how class closures for signals are actually implemented in GObject.
For example, class closures for signals (see g_signal_type_cclosure_new())
retrieve the callback function from a fixed offset in the class structure.
The meta marshaller retrieves the right callback and passes it to the
marshaller as the @marshal_data argument.
</para>
@closure: a #GClosure