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GParamSpec: add g_param_spec_get_default_value()

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The way of getting the default value out of a GParamSpec is to allocate
a GValue, initialise it, then call g_param_spec_set_default() to set the
default value into that GValue.

This is exactly how we handle setting the default value for all of the
construct properties that were not explicitly passed to g_object_new().

Instead of doing the alloc/init/store on all construct properties on
every call to g_object_new(), we can cache those GValues in the private
data of the GParamSpec itself and reuse them.

This patch does not actually make that change to g_object_new() yet, but
it adds the API to GParamSpec so that a future patch to GObject can make
the change.

https://bugzilla.gnome.org/show_bug.cgi?id=698056
This commit is contained in:
Ryan Lortie
2013-04-23 11:11:20 -04:00
parent c30c0bb34d
commit c18462b580
4 changed files with 81 additions and 1 deletions
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62
gobject/gparam.c
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@@ -80,6 +80,13 @@ static gchar* value_param_lcopy_value (const GValue *value,
GTypeCValue *collect_values,
guint collect_flags);
typedef struct
{
GValue default_value;
} GParamSpecPrivate;
static gint g_param_private_offset;
#define PRIV(inst) (&G_STRUCT_MEMBER(GParamSpecPrivate, (inst), g_param_private_offset))
/* --- functions --- */
void
@@ -147,6 +154,9 @@ g_param_spec_class_init (GParamSpecClass *class,
class->value_set_default = NULL;
class->value_validate = NULL;
class->values_cmp = NULL;
g_type_class_add_private (class, sizeof (GParamSpecPrivate));
g_param_private_offset = g_type_class_get_instance_private_offset (class);
}
static void
@@ -168,6 +178,11 @@ g_param_spec_init (GParamSpec *pspec,
static void
g_param_spec_finalize (GParamSpec *pspec)
{
GParamSpecPrivate *priv = PRIV (pspec);
if (priv->default_value.g_type)
g_value_reset (&priv->default_value);
g_datalist_clear (&pspec->qdata);
if (!(pspec->flags & G_PARAM_STATIC_NICK))
@@ -1506,3 +1521,50 @@ g_value_dup_param (const GValue *value)
return value->data[0].v_pointer ? g_param_spec_ref (value->data[0].v_pointer) : NULL;
}
/**
* g_param_get_default_value:
* @param: a #GParamSpec
*
* Gets the default value of @param as a pointer to a #GValue.
*
* The #GValue will remain value for the life of @param.
*
* Returns: a pointer to a #GValue which must not be modified
*
* Since: 2.38
**/
const GValue *
g_param_spec_get_default_value (GParamSpec *pspec)
{
GParamSpecPrivate *priv = PRIV (pspec);
/* We use the type field of the GValue as the key for the once because
* it will be zero before it is initialised and non-zero after. We
* have to take care that we don't write a non-zero value to the type
* field before we are completely done, however, because then another
* thread could come along and find the value partially-initialised.
*
* In order to accomplish this we store the default value in a
* stack-allocated GValue. We then set the type field in that value
* to zero and copy the contents into place. We then end by storing
* the type as the last step in order to ensure that we're completely
* done before a g_once_init_enter() could take the fast path in
* another thread.
*/
if (g_once_init_enter (&priv->default_value.g_type))
{
GValue default_value = G_VALUE_INIT;
g_value_init (&default_value, pspec->value_type);
g_param_value_set_default (pspec, &default_value);
/* store all but the type */
default_value.g_type = 0;
priv->default_value = default_value;
g_once_init_leave (&priv->default_value.g_type, pspec->value_type);
}
return &priv->default_value;
}