1 /* GIO - GLib Input, Output and Streaming Library
2 *
3 * Copyright (C) 2006-2007 Red Hat, Inc.
4 *
5 * SPDX-License-Identifier: LGPL-2.1-or-later
6 *
7 * This library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * This library is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General
18 * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
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 * GAsyncResult:
31 *
32 * `GAsyncResult` provides a base class for implementing asynchronous function results.
33 *
34 * Asynchronous operations are broken up into two separate operations
35 * which are chained together by a `GAsyncReadyCallback`. To begin
36 * an asynchronous operation, provide a `GAsyncReadyCallback` to the
37 * asynchronous function. This callback will be triggered when the
38 * operation has completed, and must be run in a later iteration of
39 * the thread-default main context (see
40 * [method@GLib.MainContext.push_thread_default]) from where the operation was
41 * initiated. It will be passed a `GAsyncResult` instance filled with the
42 * details of the operation's success or failure, the object the asynchronous
43 * function was started for and any error codes returned. The asynchronous
44 * callback function is then expected to call the corresponding `_finish()`
45 * function, passing the object the function was called for, the
46 * `GAsyncResult` instance, and (optionally) an @error to grab any
47 * 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 [class@Gio.FileEnumerator] 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 * ```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
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 }