gio/gasyncresult.c

   1 /* GIO - GLib Input, Output and Streaming Library
   2  *
   3  * Copyright (C) 2006-2007 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 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, write to the
  17  * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  18  * Boston, MA 02111-1307, USA.
  19  *
  20  * Author: Alexander Larsson <alexl@redhat.com>
  21  */
  22
  23 #include "config.h"
  24 #include "gasyncresult.h"
  25 #include "gsimpleasyncresult.h"
  26 #include "glibintl.h"
  27
  28
  29 /**
  30  * SECTION:gasyncresult
  31  * @short_description: Asynchronous Function Results
  32  * @include: gio/gio.h
  33  * @see_also: #GTask
  34  *
  35  * Provides a base class for implementing asynchronous function results.
  36  *
  37  * Asynchronous operations are broken up into two separate operations
  38  * which are chained together by a #GAsyncReadyCallback. To begin
  39  * an asynchronous operation, provide a #GAsyncReadyCallback to the
  40  * asynchronous function. This callback will be triggered when the
  41  * operation has completed, and will be passed a #GAsyncResult instance
  42  * filled with the details of the operation's success or failure, the
  43  * object the asynchronous function was started for and any error codes
  44  * returned. The asynchronous callback function is then expected to call
  45  * the corresponding "_finish()" function, passing the object the
  46  * function was called for, the #GAsyncResult instance, and (optionally)
  47  * an @error to grab any error conditions that may have occurred.
  48  *
  49  * The "_finish()" function for an operation takes the generic result
  50  * (of type #GAsyncResult) and returns the specific result that the
  51  * operation in question yields (e.g. a #GFileEnumerator for a
  52  * "enumerate children" operation). If the result or error status of the
  53  * operation is not needed, there is no need to call the "_finish()"
  54  * function; GIO will take care of cleaning up the result and error
  55  * information after the #GAsyncReadyCallback returns. You can pass
  56  * %NULL for the #GAsyncReadyCallback if you don't need to take any
  57  * action at all after the operation completes. Applications may also
  58  * take a reference to the #GAsyncResult and call "_finish()" later;
  59  * however, the "_finish()" function may be called at most once.
  60  *
  61  * Example of a typical asynchronous operation flow:
  62  * |[
  63  * void _theoretical_frobnitz_async (Theoretical         *t,
  64  *                                   GCancellable        *c,
  65  *                                   GAsyncReadyCallback *cb,
  66  *                                   gpointer             u);
  67  *
  68  * gboolean _theoretical_frobnitz_finish (Theoretical   *t,
  69  *                                        GAsyncResult  *res,
  70  *                                        GError       **e);
  71  *
  72  * static void
  73  * frobnitz_result_func (GObject      *source_object,
  74  *                       GAsyncResult *res,
  75  *                       gpointer      user_data)
  76  * {
  77  *   gboolean success = FALSE;
  78  *
  79  *   success = _theoretical_frobnitz_finish (source_object, res, NULL);
  80  *
  81  *   if (success)
  82  *     g_printf ("Hurray!\n");
  83  *   else
  84  *     g_printf ("Uh oh!\n");
  85  *
  86  *   /<!-- -->* ... *<!-- -->/
  87  *
  88  * }
  89  *
  90  * int main (int argc, void *argv[])
  91  * {
  92  *    /<!-- -->* ... *<!-- -->/
  93  *
  94  *    _theoretical_frobnitz_async (theoretical_data,
  95  *                                 NULL,
  96  *                                 frobnitz_result_func,
  97  *                                 NULL);
  98  *
  99  *    /<!-- -->* ... *<!-- -->/
 100  * }
 101  * ]|
 102  *
 103  * The callback for an asynchronous operation is called only once, and is
 104  * always called, even in the case of a cancelled operation. On cancellation
 105  * the result is a %G_IO_ERROR_CANCELLED error.
 106  *
 107  * <para id="io-priority"><indexterm><primary>I/O
 108  * priority</primary></indexterm> Many I/O-related asynchronous
 109  * operations have a priority parameter, which is used in certain
 110  * cases to determine the order in which operations are executed. They
 111  * are <emphasis>not</emphasis> used to determine system-wide I/O
 112  * scheduling. Priorities are integers, with lower numbers indicating
 113  * higher priority. It is recommended to choose priorities between
 114  * %G_PRIORITY_LOW and %G_PRIORITY_HIGH, with %G_PRIORITY_DEFAULT as a
 115  * default. </para>
 116  **/
 117
 118 typedef GAsyncResultIface GAsyncResultInterface;
 119 G_DEFINE_INTERFACE (GAsyncResult, g_async_result, G_TYPE_OBJECT)
 120
 121 static void
 122 g_async_result_default_init (GAsyncResultInterface *iface)
 123 {
 124 }
 125
 126 /**
 127  * g_async_result_get_user_data:
 128  * @res: a #GAsyncResult.
 129  *
 130  * Gets the user data from a #GAsyncResult.
 131  *
 132  * Returns: (transfer full): the user data for @res.
 133  **/
 134 gpointer
 135 g_async_result_get_user_data (GAsyncResult *res)
 136 {
 137   GAsyncResultIface *iface;
 138
 139   g_return_val_if_fail (G_IS_ASYNC_RESULT (res), NULL);
 140
 141   iface = G_ASYNC_RESULT_GET_IFACE (res);
 142
 143   return (* iface->get_user_data) (res);
 144 }
 145
 146 /**
 147  * g_async_result_get_source_object:
 148  * @res: a #GAsyncResult
 149  *
 150  * Gets the source object from a #GAsyncResult.
 151  *
 152  * Returns: (transfer full): a new reference to the source object for the @res,
 153  *    or %NULL if there is none.
 154  */
 155 GObject *
 156 g_async_result_get_source_object (GAsyncResult *res)
 157 {
 158   GAsyncResultIface *iface;
 159
 160   g_return_val_if_fail (G_IS_ASYNC_RESULT (res), NULL);
 161
 162   iface = G_ASYNC_RESULT_GET_IFACE (res);
 163
 164   return (* iface->get_source_object) (res);
 165 }
 166
 167 /**
 168  * g_async_result_legacy_propagate_error:
 169  * @res: a #GAsyncResult
 170  * @error: (out): a location to propagate the error to.
 171  *
 172  * If @res is a #GSimpleAsyncResult, this is equivalent to
 173  * g_simple_async_result_propagate_error(). Otherwise it returns
 174  * %FALSE.
 175  *
 176  * This can be used for legacy error handling in async
 177  * <literal>_finish ()</literal> wrapper functions that traditionally
 178  * handled #GSimpleAsyncResult error returns themselves rather than
 179  * calling into the virtual method. This should not be used in new
 180  * code; #GAsyncResult errors that are set by virtual methods should
 181  * also be extracted by virtual methods, to enable subclasses to chain
 182  * up correctly.
 183  *
 184  * Returns: %TRUE if @error is has been filled in with an error from
 185  *   @res, %FALSE if not.
 186  *
 187  * Since: 2.34
 188  **/
 189 gboolean
 190 g_async_result_legacy_propagate_error (GAsyncResult  *res,
 191                                        GError       **error)
 192 {
 193   /* This doesn't use a vmethod, because it's only for code that used
 194    * to use GSimpleAsyncResult. (But it's a GAsyncResult method so
 195    * that callers don't need to worry about GSimpleAsyncResult
 196    * deprecation warnings in the future.)
 197    */
 198
 199   if (G_IS_SIMPLE_ASYNC_RESULT (res))
 200     {
 201       return g_simple_async_result_propagate_error (G_SIMPLE_ASYNC_RESULT (res),
 202                                                     error);
 203     }
 204   else
 205     return FALSE;
 206 }
 207
 208 /**
 209  * g_async_result_is_tagged:
 210  * @res: a #GAsyncResult
 211  * @source_tag: an application-defined tag
 212  *
 213  * Checks if @res has the given @source_tag (generally a function
 214  * pointer indicating the function @res was created by).
 215  *
 216  * Returns: %TRUE if @res has the indicated @source_tag, %FALSE if
 217  *   not.
 218  *
 219  * Since: 2.34
 220  **/
 221 gboolean
 222 g_async_result_is_tagged (GAsyncResult  *res,
 223                           gpointer       source_tag)
 224 {
 225   GAsyncResultIface *iface;
 226
 227   g_return_val_if_fail (G_IS_ASYNC_RESULT (res), FALSE);
 228
 229   iface = G_ASYNC_RESULT_GET_IFACE (res);
 230
 231   if (!iface->is_tagged)
 232     return FALSE;
 233
 234   return (* iface->is_tagged) (res, source_tag);
 235 }