1 /* GIO - GLib Input, Output and Streaming Library
3 * Copyright (C) 2006-2007 Red Hat, Inc.
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.
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.
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/>.
18 * Author: Alexander Larsson <alexl@redhat.com>
22 #include "gasyncresult.h"
23 #include "gsimpleasyncresult.h"
28 * SECTION:gasyncresult
29 * @short_description: Asynchronous Function Results
33 * Provides a base class for implementing asynchronous function results.
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.
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.
59 * Example of a typical asynchronous operation flow:
61 * void _theoretical_frobnitz_async (Theoretical *t,
63 * GAsyncReadyCallback cb,
66 * gboolean _theoretical_frobnitz_finish (Theoretical *t,
71 * frobnitz_result_func (GObject *source_object,
75 * gboolean success = FALSE;
77 * success = _theoretical_frobnitz_finish (source_object, res, NULL);
80 * g_printf ("Hurray!\n");
82 * g_printf ("Uh oh!\n");
84 * /<!-- -->* ... *<!-- -->/
88 * int main (int argc, void *argv[])
90 * /<!-- -->* ... *<!-- -->/
92 * _theoretical_frobnitz_async (theoretical_data,
94 * frobnitz_result_func,
97 * /<!-- -->* ... *<!-- -->/
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.
105 * <para id="io-priority"><indexterm><primary>I/O
106 * priority</primary></indexterm> Many I/O-related asynchronous
107 * operations have a priority parameter, which is used in certain
108 * cases to determine the order in which operations are executed.
109 * They are not used to determine system-wide I/O scheduling.
110 * Priorities are integers, with lower numbers indicating higher priority.
111 * It is recommended to choose priorities between %G_PRIORITY_LOW and
112 * %G_PRIORITY_HIGH, with %G_PRIORITY_DEFAULT as a default.</para>
115 typedef GAsyncResultIface GAsyncResultInterface;
116 G_DEFINE_INTERFACE (GAsyncResult, g_async_result, G_TYPE_OBJECT)
119 g_async_result_default_init (GAsyncResultInterface *iface)
124 * g_async_result_get_user_data:
125 * @res: a #GAsyncResult.
127 * Gets the user data from a #GAsyncResult.
129 * Returns: (transfer full): the user data for @res.
132 g_async_result_get_user_data (GAsyncResult *res)
134 GAsyncResultIface *iface;
136 g_return_val_if_fail (G_IS_ASYNC_RESULT (res), NULL);
138 iface = G_ASYNC_RESULT_GET_IFACE (res);
140 return (* iface->get_user_data) (res);
144 * g_async_result_get_source_object:
145 * @res: a #GAsyncResult
147 * Gets the source object from a #GAsyncResult.
149 * Returns: (transfer full): a new reference to the source object for the @res,
150 * or %NULL if there is none.
153 g_async_result_get_source_object (GAsyncResult *res)
155 GAsyncResultIface *iface;
157 g_return_val_if_fail (G_IS_ASYNC_RESULT (res), NULL);
159 iface = G_ASYNC_RESULT_GET_IFACE (res);
161 return (* iface->get_source_object) (res);
165 * g_async_result_legacy_propagate_error:
166 * @res: a #GAsyncResult
167 * @error: (out): a location to propagate the error to.
169 * If @res is a #GSimpleAsyncResult, this is equivalent to
170 * g_simple_async_result_propagate_error(). Otherwise it returns
173 * This can be used for legacy error handling in async
174 * <literal>_finish ()</literal> wrapper functions that traditionally
175 * handled #GSimpleAsyncResult error returns themselves rather than
176 * calling into the virtual method. This should not be used in new
177 * code; #GAsyncResult errors that are set by virtual methods should
178 * also be extracted by virtual methods, to enable subclasses to chain
181 * Returns: %TRUE if @error is has been filled in with an error from
182 * @res, %FALSE if not.
187 g_async_result_legacy_propagate_error (GAsyncResult *res,
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.)
196 if (G_IS_SIMPLE_ASYNC_RESULT (res))
198 return g_simple_async_result_propagate_error (G_SIMPLE_ASYNC_RESULT (res),
206 * g_async_result_is_tagged:
207 * @res: a #GAsyncResult
208 * @source_tag: an application-defined tag
210 * Checks if @res has the given @source_tag (generally a function
211 * pointer indicating the function @res was created by).
213 * Returns: %TRUE if @res has the indicated @source_tag, %FALSE if
219 g_async_result_is_tagged (GAsyncResult *res,
222 GAsyncResultIface *iface;
224 g_return_val_if_fail (G_IS_ASYNC_RESULT (res), FALSE);
226 iface = G_ASYNC_RESULT_GET_IFACE (res);
228 if (!iface->is_tagged)
231 return (* iface->is_tagged) (res, source_tag);