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 #ifdef HAVE_UNISTD_H
25 #include <unistd.h>
26 #endif
27 #include <fcntl.h>
28 #include <gioerror.h>
29 #ifdef G_OS_WIN32
30 #include <io.h>
31 #ifndef pipe
32 #define pipe(fds) _pipe(fds, 4096, _O_BINARY)
33 #endif
34 #endif
35 #include "gcancellable.h"
36 #include "glibintl.h"
37
38 #include "gioalias.h"
39
40 /**
41 * SECTION:gcancellable
42 * @short_description: Thread-safe Operation Cancellation Stack
43 * @include: gio/gio.h
44 *
45 * GCancellable is a thread-safe operation cancellation stack used
46 * throughout GIO to allow for cancellation of synchronous and
47 * asynchronous operations.
48 */
49
50 enum {
51 CANCELLED,
52 LAST_SIGNAL
53 };
54
55 struct _GCancellable
56 {
57 GObject parent_instance;
58
59 guint cancelled : 1;
60 guint allocated_pipe : 1;
61 int cancel_pipe[2];
62
63 #ifdef G_OS_WIN32
64 GIOChannel *read_channel;
65 #endif
66 };
67
68 static guint signals[LAST_SIGNAL] = { 0 };
69
70 G_DEFINE_TYPE (GCancellable, g_cancellable, G_TYPE_OBJECT);
71
72 static GStaticPrivate current_cancellable = G_STATIC_PRIVATE_INIT;
73 G_LOCK_DEFINE_STATIC(cancellable);
74
75 static void
g_cancellable_finalize(GObject * object)76 g_cancellable_finalize (GObject *object)
77 {
78 GCancellable *cancellable = G_CANCELLABLE (object);
79
80 if (cancellable->cancel_pipe[0] != -1)
81 close (cancellable->cancel_pipe[0]);
82
83 if (cancellable->cancel_pipe[1] != -1)
84 close (cancellable->cancel_pipe[1]);
85
86 #ifdef G_OS_WIN32
87 if (cancellable->read_channel)
88 g_io_channel_unref (cancellable->read_channel);
89 #endif
90
91 G_OBJECT_CLASS (g_cancellable_parent_class)->finalize (object);
92 }
93
94 static void
g_cancellable_class_init(GCancellableClass * klass)95 g_cancellable_class_init (GCancellableClass *klass)
96 {
97 GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
98
99 gobject_class->finalize = g_cancellable_finalize;
100
101 /**
102 * GCancellable::cancelled:
103 * @cancellable: a #GCancellable.
104 *
105 * Emitted when the operation has been cancelled.
106 *
107 * Can be used by implementations of cancellable operations. If the
108 * operation is cancelled from another thread, the signal will be
109 * emitted in the thread that cancelled the operation, not the
110 * thread that is running the operation.
111 *
112 * Note that disconnecting from this signal (or any signal) in a
113 * multi-threaded program is prone to race conditions, and it is
114 * possible that a signal handler may be invoked even
115 * <emphasis>after</emphasis> a call to
116 * g_signal_handler_disconnect() for that handler has already
117 * returned. Therefore, code such as the following is wrong in a
118 * multi-threaded program:
119 *
120 * |[
121 * my_data = my_data_new (...);
122 * id = g_signal_connect (cancellable, "cancelled",
123 * G_CALLBACK (cancelled_handler), my_data);
124 *
125 * /<!-- -->* cancellable operation here... *<!-- -->/
126 *
127 * g_signal_handler_disconnect (cancellable, id);
128 * my_data_free (my_data); /<!-- -->* WRONG! *<!-- -->/
129 * /<!-- -->* if g_cancellable_cancel() is called from another
130 * * thread, cancelled_handler() may be running at this point,
131 * * so it's not safe to free my_data.
132 * *<!-- -->/
133 * ]|
134 *
135 * The correct way to free data (or otherwise clean up temporary
136 * state) in this situation is to use g_signal_connect_data() (or
137 * g_signal_connect_closure()) to connect to the signal, and do the
138 * cleanup from a #GClosureNotify, which will not be called until
139 * after the signal handler is both removed and not running:
140 *
141 * |[
142 * static void
143 * cancelled_disconnect_notify (gpointer my_data, GClosure *closure)
144 * {
145 * my_data_free (my_data);
146 * }
147 *
148 * ...
149 *
150 * my_data = my_data_new (...);
151 * id = g_signal_connect_data (cancellable, "cancelled",
152 * G_CALLBACK (cancelled_handler), my_data,
153 * cancelled_disconnect_notify, 0);
154 *
155 * /<!-- -->* cancellable operation here... *<!-- -->/
156 *
157 * g_signal_handler_disconnect (cancellable, id);
158 * /<!-- -->* cancelled_disconnect_notify() may or may not have
159 * * already been called at this point, so the code has to treat
160 * * my_data as though it has been freed.
161 * *<!-- -->/
162 * ]|
163 */
164 signals[CANCELLED] =
165 g_signal_new (I_("cancelled"),
166 G_TYPE_FROM_CLASS (gobject_class),
167 G_SIGNAL_RUN_LAST,
168 G_STRUCT_OFFSET (GCancellableClass, cancelled),
169 NULL, NULL,
170 g_cclosure_marshal_VOID__VOID,
171 G_TYPE_NONE, 0);
172
173 }
174
175 static void
set_fd_nonblocking(int fd)176 set_fd_nonblocking (int fd)
177 {
178 #ifdef F_GETFL
179 glong fcntl_flags;
180 fcntl_flags = fcntl (fd, F_GETFL);
181
182 #ifdef O_NONBLOCK
183 fcntl_flags |= O_NONBLOCK;
184 #else
185 fcntl_flags |= O_NDELAY;
186 #endif
187
188 fcntl (fd, F_SETFL, fcntl_flags);
189 #endif
190 }
191
192 static void
g_cancellable_open_pipe(GCancellable * cancellable)193 g_cancellable_open_pipe (GCancellable *cancellable)
194 {
195 if (pipe (cancellable->cancel_pipe) == 0)
196 {
197 /* Make them nonblocking, just to be sure we don't block
198 * on errors and stuff
199 */
200 set_fd_nonblocking (cancellable->cancel_pipe[0]);
201 set_fd_nonblocking (cancellable->cancel_pipe[1]);
202 }
203 else
204 g_warning ("Failed to create pipe for GCancellable. Out of file descriptors?");
205 }
206
207 static void
g_cancellable_init(GCancellable * cancellable)208 g_cancellable_init (GCancellable *cancellable)
209 {
210 cancellable->cancel_pipe[0] = -1;
211 cancellable->cancel_pipe[1] = -1;
212 }
213
214 /**
215 * g_cancellable_new:
216 *
217 * Creates a new #GCancellable object.
218 *
219 * Applications that want to start one or more operations
220 * that should be cancellable should create a #GCancellable
221 * and pass it to the operations.
222 *
223 * One #GCancellable can be used in multiple consecutive
224 * operations, but not in multiple concurrent operations.
225 *
226 * Returns: a #GCancellable.
227 **/
228 GCancellable *
g_cancellable_new(void)229 g_cancellable_new (void)
230 {
231 return g_object_new (G_TYPE_CANCELLABLE, NULL);
232 }
233
234 /**
235 * g_cancellable_push_current:
236 * @cancellable: optional #GCancellable object, %NULL to ignore.
237 *
238 * Pushes @cancellable onto the cancellable stack. The current
239 * cancllable can then be recieved using g_cancellable_get_current().
240 *
241 * This is useful when implementing cancellable operations in
242 * code that does not allow you to pass down the cancellable object.
243 *
244 * This is typically called automatically by e.g. #GFile operations,
245 * so you rarely have to call this yourself.
246 **/
247 void
g_cancellable_push_current(GCancellable * cancellable)248 g_cancellable_push_current (GCancellable *cancellable)
249 {
250 GSList *l;
251
252 g_return_if_fail (cancellable != NULL);
253
254 l = g_static_private_get (¤t_cancellable);
255 l = g_slist_prepend (l, cancellable);
256 g_static_private_set (¤t_cancellable, l, NULL);
257 }
258
259 /**
260 * g_cancellable_pop_current:
261 * @cancellable: optional #GCancellable object, %NULL to ignore.
262 *
263 * Pops @cancellable off the cancellable stack (verifying that @cancellable
264 * is on the top of the stack).
265 **/
266 void
g_cancellable_pop_current(GCancellable * cancellable)267 g_cancellable_pop_current (GCancellable *cancellable)
268 {
269 GSList *l;
270
271 l = g_static_private_get (¤t_cancellable);
272
273 g_return_if_fail (l != NULL);
274 g_return_if_fail (l->data == cancellable);
275
276 l = g_slist_delete_link (l, l);
277 g_static_private_set (¤t_cancellable, l, NULL);
278 }
279
280 /**
281 * g_cancellable_get_current:
282 *
283 * Gets the top cancellable from the stack.
284 *
285 * Returns: a #GCancellable from the top of the stack, or %NULL
286 * if the stack is empty.
287 **/
288 GCancellable *
g_cancellable_get_current(void)289 g_cancellable_get_current (void)
290 {
291 GSList *l;
292
293 l = g_static_private_get (¤t_cancellable);
294 if (l == NULL)
295 return NULL;
296
297 return G_CANCELLABLE (l->data);
298 }
299
300 /**
301 * g_cancellable_reset:
302 * @cancellable: a #GCancellable object.
303 *
304 * Resets @cancellable to its uncancelled state.
305 **/
306 void
g_cancellable_reset(GCancellable * cancellable)307 g_cancellable_reset (GCancellable *cancellable)
308 {
309 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
310
311 G_LOCK(cancellable);
312 /* Make sure we're not leaving old cancel state around */
313 if (cancellable->cancelled)
314 {
315 char ch;
316 #ifdef G_OS_WIN32
317 if (cancellable->read_channel)
318 {
319 gsize bytes_read;
320 g_io_channel_read_chars (cancellable->read_channel, &ch, 1,
321 &bytes_read, NULL);
322 }
323 else
324 #endif
325 if (cancellable->cancel_pipe[0] != -1)
326 read (cancellable->cancel_pipe[0], &ch, 1);
327 cancellable->cancelled = FALSE;
328 }
329 G_UNLOCK(cancellable);
330 }
331
332 /**
333 * g_cancellable_is_cancelled:
334 * @cancellable: a #GCancellable or NULL.
335 *
336 * Checks if a cancellable job has been cancelled.
337 *
338 * Returns: %TRUE if @cancellable is cancelled,
339 * FALSE if called with %NULL or if item is not cancelled.
340 **/
341 gboolean
g_cancellable_is_cancelled(GCancellable * cancellable)342 g_cancellable_is_cancelled (GCancellable *cancellable)
343 {
344 return cancellable != NULL && cancellable->cancelled;
345 }
346
347 /**
348 * g_cancellable_set_error_if_cancelled:
349 * @cancellable: a #GCancellable object.
350 * @error: #GError to append error state to.
351 *
352 * If the @cancellable is cancelled, sets the error to notify
353 * that the operation was cancelled.
354 *
355 * Returns: %TRUE if @cancellable was cancelled, %FALSE if it was not.
356 **/
357 gboolean
g_cancellable_set_error_if_cancelled(GCancellable * cancellable,GError ** error)358 g_cancellable_set_error_if_cancelled (GCancellable *cancellable,
359 GError **error)
360 {
361 if (g_cancellable_is_cancelled (cancellable))
362 {
363 g_set_error_literal (error,
364 G_IO_ERROR,
365 G_IO_ERROR_CANCELLED,
366 _("Operation was cancelled"));
367 return TRUE;
368 }
369
370 return FALSE;
371 }
372
373 /**
374 * g_cancellable_get_fd:
375 * @cancellable: a #GCancellable.
376 *
377 * Gets the file descriptor for a cancellable job. This can be used to
378 * implement cancellable operations on Unix systems. The returned fd will
379 * turn readable when @cancellable is cancelled.
380 *
381 * See also g_cancellable_make_pollfd().
382 *
383 * Returns: A valid file descriptor. %-1 if the file descriptor
384 * is not supported, or on errors.
385 **/
386 int
g_cancellable_get_fd(GCancellable * cancellable)387 g_cancellable_get_fd (GCancellable *cancellable)
388 {
389 int fd;
390 if (cancellable == NULL)
391 return -1;
392
393 G_LOCK(cancellable);
394 if (!cancellable->allocated_pipe)
395 {
396 cancellable->allocated_pipe = TRUE;
397 g_cancellable_open_pipe (cancellable);
398 }
399
400 fd = cancellable->cancel_pipe[0];
401 G_UNLOCK(cancellable);
402
403 return fd;
404 }
405
406 /**
407 * g_cancellable_make_pollfd:
408 * @cancellable: a #GCancellable.
409 * @pollfd: a pointer to a #GPollFD
410 *
411 * Creates a #GPollFD corresponding to @cancellable; this can be passed
412 * to g_poll() and used to poll for cancellation.
413 **/
414 void
g_cancellable_make_pollfd(GCancellable * cancellable,GPollFD * pollfd)415 g_cancellable_make_pollfd (GCancellable *cancellable, GPollFD *pollfd)
416 {
417 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
418 g_return_if_fail (pollfd != NULL);
419
420 #ifdef G_OS_WIN32
421 if (!cancellable->read_channel)
422 {
423 int fd = g_cancellable_get_fd (cancellable);
424 cancellable->read_channel = g_io_channel_win32_new_fd (fd);
425 g_io_channel_set_buffered (cancellable->read_channel, FALSE);
426 g_io_channel_set_flags (cancellable->read_channel,
427 G_IO_FLAG_NONBLOCK, NULL);
428 g_io_channel_set_encoding (cancellable->read_channel, NULL, NULL);
429 }
430 g_io_channel_win32_make_pollfd (cancellable->read_channel, G_IO_IN, pollfd);
431 /* (We need to keep cancellable->read_channel around, because it's
432 * keeping track of state related to the pollfd.)
433 */
434 #else /* !G_OS_WIN32 */
435 pollfd->fd = g_cancellable_get_fd (cancellable);
436 pollfd->events = G_IO_IN;
437 #endif /* G_OS_WIN32 */
438 pollfd->revents = 0;
439 }
440
441 /**
442 * g_cancellable_cancel:
443 * @cancellable: a #GCancellable object.
444 *
445 * Will set @cancellable to cancelled, and will emit the
446 * #GCancellable::cancelled signal. (However, see the warning about
447 * race conditions in the documentation for that signal if you are
448 * planning to connect to it.)
449 *
450 * This function is thread-safe. In other words, you can safely call
451 * it from a thread other than the one running the operation that was
452 * passed the @cancellable.
453 *
454 * The convention within gio is that cancelling an asynchronous
455 * operation causes it to complete asynchronously. That is, if you
456 * cancel the operation from the same thread in which it is running,
457 * then the operation's #GAsyncReadyCallback will not be invoked until
458 * the application returns to the main loop.
459 **/
460 void
g_cancellable_cancel(GCancellable * cancellable)461 g_cancellable_cancel (GCancellable *cancellable)
462 {
463 gboolean cancel;
464
465 cancel = FALSE;
466
467 G_LOCK(cancellable);
468 if (cancellable != NULL &&
469 !cancellable->cancelled)
470 {
471 char ch = 'x';
472 cancel = TRUE;
473 cancellable->cancelled = TRUE;
474 if (cancellable->cancel_pipe[1] != -1)
475 write (cancellable->cancel_pipe[1], &ch, 1);
476 }
477 G_UNLOCK(cancellable);
478
479 if (cancel)
480 {
481 g_object_ref (cancellable);
482 g_signal_emit (cancellable, signals[CANCELLED], 0);
483 g_object_unref (cancellable);
484 }
485 }
486
487 #define __G_CANCELLABLE_C__
488 #include "gioaliasdef.c"
489