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