gio/ginitable.c

   1 /* GIO - GLib Input, Output and Streaming Library
   2  *
   3  * Copyright (C) 2009 Red Hat, Inc.
   4  *
   5  * This library is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU Lesser General Public
   7  * License as published by the Free Software Foundation; either
   8  * version 2.1 of the License, or (at your option) any later version.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General
  16  * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
  17  *
  18  * Author: Alexander Larsson <alexl@redhat.com>
  19  */
  20
  21 #include "config.h"
  22 #include "ginitable.h"
  23 #include "glibintl.h"
  24
  25
  26 /**
  27  * SECTION:ginitable
  28  * @short_description: Failable object initialization interface
  29  * @include: gio/gio.h
  30  * @see_also: #GAsyncInitable
  31  *
  32  * #GInitable is implemented by objects that can fail during
  33  * initialization. If an object implements this interface then
  34  * it must be initialized as the first thing after construction,
  35  * either via g_initable_init() or g_async_initable_init_async()
  36  * (the latter is only available if it also implements #GAsyncInitable).
  37  *
  38  * If the object is not initialized, or initialization returns with an
  39  * error, then all operations on the object except g_object_ref() and
  40  * g_object_unref() are considered to be invalid, and have undefined
  41  * behaviour. They will often fail with g_critical() or g_warning(), but
  42  * this must not be relied on.
  43  *
  44  * Users of objects implementing this are not intended to use
  45  * the interface method directly, instead it will be used automatically
  46  * in various ways. For C applications you generally just call
  47  * g_initable_new() directly, or indirectly via a foo_thing_new() wrapper.
  48  * This will call g_initable_init() under the cover, returning %NULL and
  49  * setting a #GError on failure (at which point the instance is
  50  * unreferenced).
  51  *
  52  * For bindings in languages where the native constructor supports
  53  * exceptions the binding could check for objects implemention %GInitable
  54  * during normal construction and automatically initialize them, throwing
  55  * an exception on failure.
  56  */
  57
  58 typedef GInitableIface GInitableInterface;
  59 G_DEFINE_INTERFACE (GInitable, g_initable, G_TYPE_OBJECT)
  60
  61 static void
  62 g_initable_default_init (GInitableInterface *iface)
  63 {
  64 }
  65
  66 /**
  67  * g_initable_init:
  68  * @initable: a #GInitable.
  69  * @cancellable: optional #GCancellable object, %NULL to ignore.
  70  * @error: a #GError location to store the error occurring, or %NULL to
  71  * ignore.
  72  *
  73  * Initializes the object implementing the interface.
  74  *
  75  * This method is intended for language bindings. If writing in C,
  76  * g_initable_new() should typically be used instead.
  77  *
  78  * The object must be initialized before any real use after initial
  79  * construction, either with this function or g_async_initable_init_async().
  80  *
  81  * Implementations may also support cancellation. If @cancellable is not %NULL,
  82  * then initialization can be cancelled by triggering the cancellable object
  83  * from another thread. If the operation was cancelled, the error
  84  * %G_IO_ERROR_CANCELLED will be returned. If @cancellable is not %NULL and
  85  * the object doesn't support cancellable initialization the error
  86  * %G_IO_ERROR_NOT_SUPPORTED will be returned.
  87  *
  88  * If the object is not initialized, or initialization returns with an
  89  * error, then all operations on the object except g_object_ref() and
  90  * g_object_unref() are considered to be invalid, and have undefined
  91  * behaviour. See the [introduction][ginitable] for more details.
  92  *
  93  * Callers should not assume that a class which implements #GInitable can be
  94  * initialized multiple times, unless the class explicitly documents itself as
  95  * supporting this. Generally, a class’ implementation of init() can assume
  96  * (and assert) that it will only be called once. Previously, this documentation
  97  * recommended all #GInitable implementations should be idempotent; that
  98  * recommendation was relaxed in GLib 2.54.
  99  *
 100  * If a class explicitly supports being initialized multiple times, it is
 101  * recommended that the method is idempotent: multiple calls with the same
 102  * arguments should return the same results. Only the first call initializes
 103  * the object; further calls return the result of the first call.
 104  *
 105  * One reason why a class might need to support idempotent initialization is if
 106  * it is designed to be used via the singleton pattern, with a
 107  * #GObjectClass.constructor that sometimes returns an existing instance.
 108  * In this pattern, a caller would expect to be able to call g_initable_init()
 109  * on the result of g_object_new(), regardless of whether it is in fact a new
 110  * instance.
 111  *
 112  * Returns: %TRUE if successful. If an error has occurred, this function will
 113  *     return %FALSE and set @error appropriately if present.
 114  *
 115  * Since: 2.22
 116  */
 117 gboolean
 118 g_initable_init (GInitable     *initable,
 119                  GCancellable  *cancellable,
 120                  GError       **error)
 121 {
 122   GInitableIface *iface;
 123
 124   g_return_val_if_fail (G_IS_INITABLE (initable), FALSE);
 125
 126   iface = G_INITABLE_GET_IFACE (initable);
 127
 128   return (* iface->init) (initable, cancellable, error);
 129 }
 130
 131 /**
 132  * g_initable_new:
 133  * @object_type: a #GType supporting #GInitable.
 134  * @cancellable: optional #GCancellable object, %NULL to ignore.
 135  * @error: a #GError location to store the error occurring, or %NULL to
 136  *    ignore.
 137  * @first_property_name: (nullable): the name of the first property, or %NULL if no
 138  *     properties
 139  * @...:  the value if the first property, followed by and other property
 140  *    value pairs, and ended by %NULL.
 141  *
 142  * Helper function for constructing #GInitable object. This is
 143  * similar to g_object_new() but also initializes the object
 144  * and returns %NULL, setting an error on failure.
 145  *
 146  * Returns: (type GObject.Object) (transfer full): a newly allocated
 147  *      #GObject, or %NULL on error
 148  *
 149  * Since: 2.22
 150  */
 151 gpointer
 152 g_initable_new (GType          object_type,
 153                 GCancellable  *cancellable,
 154                 GError       **error,
 155                 const gchar   *first_property_name,
 156                 ...)
 157 {
 158   GObject *object;
 159   va_list var_args;
 160
 161   va_start (var_args, first_property_name);
 162   object = g_initable_new_valist (object_type,
 163                                   first_property_name, var_args,
 164                                   cancellable, error);
 165   va_end (var_args);
 166
 167   return object;
 168 }
 169
 170 /**
 171  * g_initable_newv:
 172  * @object_type: a #GType supporting #GInitable.
 173  * @n_parameters: the number of parameters in @parameters
 174  * @parameters: (array length=n_parameters): the parameters to use to construct the object
 175  * @cancellable: optional #GCancellable object, %NULL to ignore.
 176  * @error: a #GError location to store the error occurring, or %NULL to
 177  *     ignore.
 178  *
 179  * Helper function for constructing #GInitable object. This is
 180  * similar to g_object_newv() but also initializes the object
 181  * and returns %NULL, setting an error on failure.
 182  *
 183  * Returns: (type GObject.Object) (transfer full): a newly allocated
 184  *      #GObject, or %NULL on error
 185  *
 186  * Since: 2.22
 187  * Deprecated: 2.54: Use g_object_new_with_properties() and
 188  * g_initable_init() instead. See #GParameter for more information.
 189  */
 190 gpointer
 191 g_initable_newv (GType          object_type,
 192                  guint          n_parameters,
 193                  GParameter    *parameters,
 194                  GCancellable  *cancellable,
 195                  GError       **error)
 196 {
 197   GObject *obj;
 198
 199   g_return_val_if_fail (G_TYPE_IS_INITABLE (object_type), NULL);
 200
 201 G_GNUC_BEGIN_IGNORE_DEPRECATIONS
 202   obj = g_object_newv (object_type, n_parameters, parameters);
 203 G_GNUC_END_IGNORE_DEPRECATIONS
 204
 205   if (!g_initable_init (G_INITABLE (obj), cancellable, error))
 206     {
 207       g_object_unref (obj);
 208       return NULL;
 209     }
 210
 211   return (gpointer)obj;
 212 }
 213
 214 /**
 215  * g_initable_new_valist:
 216  * @object_type: a #GType supporting #GInitable.
 217  * @first_property_name: the name of the first property, followed by
 218  * the value, and other property value pairs, and ended by %NULL.
 219  * @var_args: The var args list generated from @first_property_name.
 220  * @cancellable: optional #GCancellable object, %NULL to ignore.
 221  * @error: a #GError location to store the error occurring, or %NULL to
 222  *     ignore.
 223  *
 224  * Helper function for constructing #GInitable object. This is
 225  * similar to g_object_new_valist() but also initializes the object
 226  * and returns %NULL, setting an error on failure.
 227  *
 228  * Returns: (type GObject.Object) (transfer full): a newly allocated
 229  *      #GObject, or %NULL on error
 230  *
 231  * Since: 2.22
 232  */
 233 GObject*
 234 g_initable_new_valist (GType          object_type,
 235                        const gchar   *first_property_name,
 236                        va_list        var_args,
 237                        GCancellable  *cancellable,
 238                        GError       **error)
 239 {
 240   GObject *obj;
 241
 242   g_return_val_if_fail (G_TYPE_IS_INITABLE (object_type), NULL);
 243
 244   obj = g_object_new_valist (object_type,
 245                              first_property_name,
 246                              var_args);
 247
 248   if (!g_initable_init (G_INITABLE (obj), cancellable, error))
 249     {
 250       g_object_unref (obj);
 251       return NULL;
 252     }
 253
 254   return obj;
 255 }