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 must be run in a later iteration of
  40  * the [thread-default main context][g-main-context-push-thread-default]
  41  * from where the operation was initiated. It will be passed a
  42  * #GAsyncResult instance filled with the details of the operation's
  43  * success or failure, the object the asynchronous function was
  44  * started for and any error codes returned. The asynchronous callback
  45  * function is then expected to call the corresponding "_finish()"
  46  * function, passing the object the function was called for, the
  47  * #GAsyncResult instance, and (optionally) an @error to grab any
  48  * error conditions that may have occurred.
  49  *
  50  * The "_finish()" function for an operation takes the generic result
  51  * (of type #GAsyncResult) and returns the specific result that the
  52  * operation in question yields (e.g. a #GFileEnumerator for a
  53  * "enumerate children" operation). If the result or error status of the
  54  * operation is not needed, there is no need to call the "_finish()"
  55  * function; GIO will take care of cleaning up the result and error
  56  * information after the #GAsyncReadyCallback returns. You can pass
  57  * %NULL for the #GAsyncReadyCallback if you don't need to take any
  58  * action at all after the operation completes. Applications may also
  59  * take a reference to the #GAsyncResult and call "_finish()" later;
  60  * however, the "_finish()" function may be called at most once.
  61  *
  62  * Example of a typical asynchronous operation flow:
  63  * |[<!-- language="C" -->
  64  * void _theoretical_frobnitz_async (Theoretical         *t,
  65  *                                   GCancellable        *c,
  66  *                                   GAsyncReadyCallback  cb,
  67  *                                   gpointer             u);
  68  *
  69  * gboolean _theoretical_frobnitz_finish (Theoretical   *t,
  70  *                                        GAsyncResult  *res,
  71  *                                        GError       **e);
  72  *
  73  * static void
  74  * frobnitz_result_func (GObject      *source_object,
  75  *                       GAsyncResult *res,
  76  *                       gpointer      user_data)
  77  * {
  78  *   gboolean success = FALSE;
  79  *
  80  *   success = _theoretical_frobnitz_finish (source_object, res, NULL);
  81  *
  82  *   if (success)
  83  *     g_printf ("Hurray!\n");
  84  *   else
  85  *     g_printf ("Uh oh!\n");
  86  *
  87  *   ...
  88  *
  89  * }
  90  *
  91  * int main (int argc, void *argv[])
  92  * {
  93  *    ...
  94  *
  95  *    _theoretical_frobnitz_async (theoretical_data,
  96  *                                 NULL,
  97  *                                 frobnitz_result_func,
  98  *                                 NULL);
  99  *
 100  *    ...
 101  * }
 102  * ]|
 103  *
 104  * The callback for an asynchronous operation is called only once, and is
 105  * always called, even in the case of a cancelled operation. On cancellation
 106  * the result is a %G_IO_ERROR_CANCELLED error.
 107  *
 108  * ## I/O Priority # {#io-priority}
 109  *
 110  * Many I/O-related asynchronous operations have a priority parameter,
 111  * which is used in certain cases to determine the order in which
 112  * operations are executed. They are not used to determine system-wide
 113  * I/O scheduling. Priorities are integers, with lower numbers indicating
 114  * higher priority. It is recommended to choose priorities between
 115  * %G_PRIORITY_LOW and %G_PRIORITY_HIGH, with %G_PRIORITY_DEFAULT
 116  * as a default.
 117  */
 118
 119 typedef GAsyncResultIface GAsyncResultInterface;
 120 G_DEFINE_INTERFACE (GAsyncResult, g_async_result, G_TYPE_OBJECT)
 121
 122 static void
 123 g_async_result_default_init (GAsyncResultInterface *iface)
 124 {
 125 }
 126
 127 /**
 128  * g_async_result_get_user_data:
 129  * @res: a #GAsyncResult.
 130  *
 131  * Gets the user data from a #GAsyncResult.
 132  *
 133  * Returns: (transfer full): the user data for @res.
 134  **/
 135 gpointer
 136 g_async_result_get_user_data (GAsyncResult *res)
 137 {
 138   GAsyncResultIface *iface;
 139
 140   g_return_val_if_fail (G_IS_ASYNC_RESULT (res), NULL);
 141
 142   iface = G_ASYNC_RESULT_GET_IFACE (res);
 143
 144   return (* iface->get_user_data) (res);
 145 }
 146
 147 /**
 148  * g_async_result_get_source_object:
 149  * @res: a #GAsyncResult
 150  *
 151  * Gets the source object from a #GAsyncResult.
 152  *
 153  * Returns: (transfer full) (nullable): a new reference to the source
 154  *    object for the @res, or %NULL if there is none.
 155  */
 156 GObject *
 157 g_async_result_get_source_object (GAsyncResult *res)
 158 {
 159   GAsyncResultIface *iface;
 160
 161   g_return_val_if_fail (G_IS_ASYNC_RESULT (res), NULL);
 162
 163   iface = G_ASYNC_RESULT_GET_IFACE (res);
 164
 165   return (* iface->get_source_object) (res);
 166 }
 167
 168 /**
 169  * g_async_result_legacy_propagate_error:
 170  * @res: a #GAsyncResult
 171  * @error: (out): a location to propagate the error to.
 172  *
 173  * If @res is a #GSimpleAsyncResult, this is equivalent to
 174  * g_simple_async_result_propagate_error(). Otherwise it returns
 175  * %FALSE.
 176  *
 177  * This can be used for legacy error handling in async *_finish()
 178  * wrapper functions that traditionally handled #GSimpleAsyncResult
 179  * error returns themselves rather than calling into the virtual method.
 180  * This should not be used in new code; #GAsyncResult errors that are
 181  * set by virtual methods should also be extracted by virtual methods,
 182  * to enable subclasses to chain 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   G_GNUC_BEGIN_IGNORE_DEPRECATIONS
 200   if (G_IS_SIMPLE_ASYNC_RESULT (res))
 201     {
 202       return g_simple_async_result_propagate_error (G_SIMPLE_ASYNC_RESULT (res),
 203                                                     error);
 204     }
 205   else
 206     return FALSE;
 207   G_GNUC_END_IGNORE_DEPRECATIONS
 208 }
 209
 210 /**
 211  * g_async_result_is_tagged:
 212  * @res: a #GAsyncResult
 213  * @source_tag: an application-defined tag
 214  *
 215  * Checks if @res has the given @source_tag (generally a function
 216  * pointer indicating the function @res was created by).
 217  *
 218  * Returns: %TRUE if @res has the indicated @source_tag, %FALSE if
 219  *   not.
 220  *
 221  * Since: 2.34
 222  **/
 223 gboolean
 224 g_async_result_is_tagged (GAsyncResult  *res,
 225                           gpointer       source_tag)
 226 {
 227   GAsyncResultIface *iface;
 228
 229   g_return_val_if_fail (G_IS_ASYNC_RESULT (res), FALSE);
 230
 231   iface = G_ASYNC_RESULT_GET_IFACE (res);
 232
 233   if (!iface->is_tagged)
 234     return FALSE;
 235
 236   return (* iface->is_tagged) (res, source_tag);
 237 }