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 "glib.h"
23#include <gioerror.h>
24#include "glib-private.h"
25#include "gcancellable.h"
26#include "glibintl.h"
27
28
29/**
30 * SECTION:gcancellable
31 * @short_description: Thread-safe Operation Cancellation Stack
32 * @include: gio/gio.h
33 *
34 * GCancellable is a thread-safe operation cancellation stack used
35 * throughout GIO to allow for cancellation of synchronous and
36 * asynchronous operations.
37 */
38
39enum {
40 CANCELLED,
41 LAST_SIGNAL
42};
43
44struct _GCancellablePrivate
45{
46 /* Atomic so that g_cancellable_is_cancelled does not require holding the mutex. */
47 gboolean cancelled;
48 /* Access to fields below is protected by cancellable_mutex. */
49 guint cancelled_running : 1;
50 guint cancelled_running_waiting : 1;
51
52 guint fd_refcount;
53 GWakeup *wakeup;
54};
55
56static guint signals[LAST_SIGNAL] = { 0 };
57
58G_DEFINE_TYPE_WITH_PRIVATE (GCancellable, g_cancellable, G_TYPE_OBJECT)
59
60static GPrivate current_cancellable;
61static GMutex cancellable_mutex;
62static GCond cancellable_cond;
63
64static void
65g_cancellable_finalize (GObject *object)
66{
67 GCancellable *cancellable = G_CANCELLABLE (object);
68
69 if (cancellable->priv->wakeup)
70 GLIB_PRIVATE_CALL (g_wakeup_free) (cancellable->priv->wakeup);
71
72 G_OBJECT_CLASS (g_cancellable_parent_class)->finalize (object);
73}
74
75static void
76g_cancellable_class_init (GCancellableClass *klass)
77{
78 GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
79
80 gobject_class->finalize = g_cancellable_finalize;
81
82 /**
83 * GCancellable::cancelled:
84 * @cancellable: a #GCancellable.
85 *
86 * Emitted when the operation has been cancelled.
87 *
88 * Can be used by implementations of cancellable operations. If the
89 * operation is cancelled from another thread, the signal will be
90 * emitted in the thread that cancelled the operation, not the
91 * thread that is running the operation.
92 *
93 * Note that disconnecting from this signal (or any signal) in a
94 * multi-threaded program is prone to race conditions. For instance
95 * it is possible that a signal handler may be invoked even after
96 * a call to g_signal_handler_disconnect() for that handler has
97 * already returned.
98 *
99 * There is also a problem when cancellation happens right before
100 * connecting to the signal. If this happens the signal will
101 * unexpectedly not be emitted, and checking before connecting to
102 * the signal leaves a race condition where this is still happening.
103 *
104 * In order to make it safe and easy to connect handlers there
105 * are two helper functions: g_cancellable_connect() and
106 * g_cancellable_disconnect() which protect against problems
107 * like this.
108 *
109 * An example of how to us this:
110 * |[<!-- language="C" -->
111 * // Make sure we don't do unnecessary work if already cancelled
112 * if (g_cancellable_set_error_if_cancelled (cancellable, error))
113 * return;
114 *
115 * // Set up all the data needed to be able to handle cancellation
116 * // of the operation
117 * my_data = my_data_new (...);
118 *
119 * id = 0;
120 * if (cancellable)
121 * id = g_cancellable_connect (cancellable,
122 * G_CALLBACK (cancelled_handler)
123 * data, NULL);
124 *
125 * // cancellable operation here...
126 *
127 * g_cancellable_disconnect (cancellable, id);
128 *
129 * // cancelled_handler is never called after this, it is now safe
130 * // to free the data
131 * my_data_free (my_data);
132 * ]|
133 *
134 * Note that the cancelled signal is emitted in the thread that
135 * the user cancelled from, which may be the main thread. So, the
136 * cancellable signal should not do something that can block.
137 */
138 signals[CANCELLED] =
139 g_signal_new (I_("cancelled"),
140 G_TYPE_FROM_CLASS (gobject_class),
141 signal_flags: G_SIGNAL_RUN_LAST,
142 G_STRUCT_OFFSET (GCancellableClass, cancelled),
143 NULL, NULL,
144 NULL,
145 G_TYPE_NONE, n_params: 0);
146
147}
148
149static void
150g_cancellable_init (GCancellable *cancellable)
151{
152 cancellable->priv = g_cancellable_get_instance_private (self: cancellable);
153}
154
155/**
156 * g_cancellable_new:
157 *
158 * Creates a new #GCancellable object.
159 *
160 * Applications that want to start one or more operations
161 * that should be cancellable should create a #GCancellable
162 * and pass it to the operations.
163 *
164 * One #GCancellable can be used in multiple consecutive
165 * operations or in multiple concurrent operations.
166 *
167 * Returns: a #GCancellable.
168 **/
169GCancellable *
170g_cancellable_new (void)
171{
172 return g_object_new (G_TYPE_CANCELLABLE, NULL);
173}
174
175/**
176 * g_cancellable_push_current:
177 * @cancellable: a #GCancellable object
178 *
179 * Pushes @cancellable onto the cancellable stack. The current
180 * cancellable can then be received using g_cancellable_get_current().
181 *
182 * This is useful when implementing cancellable operations in
183 * code that does not allow you to pass down the cancellable object.
184 *
185 * This is typically called automatically by e.g. #GFile operations,
186 * so you rarely have to call this yourself.
187 **/
188void
189g_cancellable_push_current (GCancellable *cancellable)
190{
191 GSList *l;
192
193 g_return_if_fail (cancellable != NULL);
194
195 l = g_private_get (key: &current_cancellable);
196 l = g_slist_prepend (list: l, data: cancellable);
197 g_private_set (key: &current_cancellable, value: l);
198}
199
200/**
201 * g_cancellable_pop_current:
202 * @cancellable: a #GCancellable object
203 *
204 * Pops @cancellable off the cancellable stack (verifying that @cancellable
205 * is on the top of the stack).
206 **/
207void
208g_cancellable_pop_current (GCancellable *cancellable)
209{
210 GSList *l;
211
212 l = g_private_get (key: &current_cancellable);
213
214 g_return_if_fail (l != NULL);
215 g_return_if_fail (l->data == cancellable);
216
217 l = g_slist_delete_link (list: l, link_: l);
218 g_private_set (key: &current_cancellable, value: l);
219}
220
221/**
222 * g_cancellable_get_current:
223 *
224 * Gets the top cancellable from the stack.
225 *
226 * Returns: (nullable) (transfer none): a #GCancellable from the top
227 * of the stack, or %NULL if the stack is empty.
228 **/
229GCancellable *
230g_cancellable_get_current (void)
231{
232 GSList *l;
233
234 l = g_private_get (key: &current_cancellable);
235 if (l == NULL)
236 return NULL;
237
238 return G_CANCELLABLE (l->data);
239}
240
241/**
242 * g_cancellable_reset:
243 * @cancellable: a #GCancellable object.
244 *
245 * Resets @cancellable to its uncancelled state.
246 *
247 * If cancellable is currently in use by any cancellable operation
248 * then the behavior of this function is undefined.
249 *
250 * Note that it is generally not a good idea to reuse an existing
251 * cancellable for more operations after it has been cancelled once,
252 * as this function might tempt you to do. The recommended practice
253 * is to drop the reference to a cancellable after cancelling it,
254 * and let it die with the outstanding async operations. You should
255 * create a fresh cancellable for further async operations.
256 **/
257void
258g_cancellable_reset (GCancellable *cancellable)
259{
260 GCancellablePrivate *priv;
261
262 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
263
264 g_mutex_lock (mutex: &cancellable_mutex);
265
266 priv = cancellable->priv;
267
268 while (priv->cancelled_running)
269 {
270 priv->cancelled_running_waiting = TRUE;
271 g_cond_wait (cond: &cancellable_cond, mutex: &cancellable_mutex);
272 }
273
274 if (g_atomic_int_get (&priv->cancelled))
275 {
276 if (priv->wakeup)
277 GLIB_PRIVATE_CALL (g_wakeup_acknowledge) (priv->wakeup);
278
279 g_atomic_int_set (&priv->cancelled, FALSE);
280 }
281
282 g_mutex_unlock (mutex: &cancellable_mutex);
283}
284
285/**
286 * g_cancellable_is_cancelled:
287 * @cancellable: (nullable): a #GCancellable or %NULL
288 *
289 * Checks if a cancellable job has been cancelled.
290 *
291 * Returns: %TRUE if @cancellable is cancelled,
292 * FALSE if called with %NULL or if item is not cancelled.
293 **/
294gboolean
295g_cancellable_is_cancelled (GCancellable *cancellable)
296{
297 return cancellable != NULL && g_atomic_int_get (&cancellable->priv->cancelled);
298}
299
300/**
301 * g_cancellable_set_error_if_cancelled:
302 * @cancellable: (nullable): a #GCancellable or %NULL
303 * @error: #GError to append error state to
304 *
305 * If the @cancellable is cancelled, sets the error to notify
306 * that the operation was cancelled.
307 *
308 * Returns: %TRUE if @cancellable was cancelled, %FALSE if it was not
309 */
310gboolean
311g_cancellable_set_error_if_cancelled (GCancellable *cancellable,
312 GError **error)
313{
314 if (g_cancellable_is_cancelled (cancellable))
315 {
316 g_set_error_literal (err: error,
317 G_IO_ERROR,
318 code: G_IO_ERROR_CANCELLED,
319 _("Operation was cancelled"));
320 return TRUE;
321 }
322
323 return FALSE;
324}
325
326/**
327 * g_cancellable_get_fd:
328 * @cancellable: a #GCancellable.
329 *
330 * Gets the file descriptor for a cancellable job. This can be used to
331 * implement cancellable operations on Unix systems. The returned fd will
332 * turn readable when @cancellable is cancelled.
333 *
334 * You are not supposed to read from the fd yourself, just check for
335 * readable status. Reading to unset the readable status is done
336 * with g_cancellable_reset().
337 *
338 * After a successful return from this function, you should use
339 * g_cancellable_release_fd() to free up resources allocated for
340 * the returned file descriptor.
341 *
342 * See also g_cancellable_make_pollfd().
343 *
344 * Returns: A valid file descriptor. `-1` if the file descriptor
345 * is not supported, or on errors.
346 **/
347int
348g_cancellable_get_fd (GCancellable *cancellable)
349{
350 GPollFD pollfd;
351#ifndef G_OS_WIN32
352 gboolean retval G_GNUC_UNUSED /* when compiling with G_DISABLE_ASSERT */;
353#endif
354
355 if (cancellable == NULL)
356 return -1;
357
358#ifdef G_OS_WIN32
359 pollfd.fd = -1;
360#else
361 retval = g_cancellable_make_pollfd (cancellable, pollfd: &pollfd);
362 g_assert (retval);
363#endif
364
365 return pollfd.fd;
366}
367
368/**
369 * g_cancellable_make_pollfd:
370 * @cancellable: (nullable): a #GCancellable or %NULL
371 * @pollfd: a pointer to a #GPollFD
372 *
373 * Creates a #GPollFD corresponding to @cancellable; this can be passed
374 * to g_poll() and used to poll for cancellation. This is useful both
375 * for unix systems without a native poll and for portability to
376 * windows.
377 *
378 * When this function returns %TRUE, you should use
379 * g_cancellable_release_fd() to free up resources allocated for the
380 * @pollfd. After a %FALSE return, do not call g_cancellable_release_fd().
381 *
382 * If this function returns %FALSE, either no @cancellable was given or
383 * resource limits prevent this function from allocating the necessary
384 * structures for polling. (On Linux, you will likely have reached
385 * the maximum number of file descriptors.) The suggested way to handle
386 * these cases is to ignore the @cancellable.
387 *
388 * You are not supposed to read from the fd yourself, just check for
389 * readable status. Reading to unset the readable status is done
390 * with g_cancellable_reset().
391 *
392 * Returns: %TRUE if @pollfd was successfully initialized, %FALSE on
393 * failure to prepare the cancellable.
394 *
395 * Since: 2.22
396 **/
397gboolean
398g_cancellable_make_pollfd (GCancellable *cancellable, GPollFD *pollfd)
399{
400 g_return_val_if_fail (pollfd != NULL, FALSE);
401 if (cancellable == NULL)
402 return FALSE;
403 g_return_val_if_fail (G_IS_CANCELLABLE (cancellable), FALSE);
404
405 g_mutex_lock (mutex: &cancellable_mutex);
406
407 cancellable->priv->fd_refcount++;
408
409 if (cancellable->priv->wakeup == NULL)
410 {
411 cancellable->priv->wakeup = GLIB_PRIVATE_CALL (g_wakeup_new) ();
412
413 if (g_atomic_int_get (&cancellable->priv->cancelled))
414 GLIB_PRIVATE_CALL (g_wakeup_signal) (cancellable->priv->wakeup);
415 }
416
417 GLIB_PRIVATE_CALL (g_wakeup_get_pollfd) (cancellable->priv->wakeup, pollfd);
418
419 g_mutex_unlock (mutex: &cancellable_mutex);
420
421 return TRUE;
422}
423
424/**
425 * g_cancellable_release_fd:
426 * @cancellable: a #GCancellable
427 *
428 * Releases a resources previously allocated by g_cancellable_get_fd()
429 * or g_cancellable_make_pollfd().
430 *
431 * For compatibility reasons with older releases, calling this function
432 * is not strictly required, the resources will be automatically freed
433 * when the @cancellable is finalized. However, the @cancellable will
434 * block scarce file descriptors until it is finalized if this function
435 * is not called. This can cause the application to run out of file
436 * descriptors when many #GCancellables are used at the same time.
437 *
438 * Since: 2.22
439 **/
440void
441g_cancellable_release_fd (GCancellable *cancellable)
442{
443 GCancellablePrivate *priv;
444
445 if (cancellable == NULL)
446 return;
447
448 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
449
450 priv = cancellable->priv;
451
452 g_mutex_lock (mutex: &cancellable_mutex);
453 g_assert (priv->fd_refcount > 0);
454
455 priv->fd_refcount--;
456 if (priv->fd_refcount == 0)
457 {
458 GLIB_PRIVATE_CALL (g_wakeup_free) (priv->wakeup);
459 priv->wakeup = NULL;
460 }
461
462 g_mutex_unlock (mutex: &cancellable_mutex);
463}
464
465/**
466 * g_cancellable_cancel:
467 * @cancellable: (nullable): a #GCancellable object.
468 *
469 * Will set @cancellable to cancelled, and will emit the
470 * #GCancellable::cancelled signal. (However, see the warning about
471 * race conditions in the documentation for that signal if you are
472 * planning to connect to it.)
473 *
474 * This function is thread-safe. In other words, you can safely call
475 * it from a thread other than the one running the operation that was
476 * passed the @cancellable.
477 *
478 * If @cancellable is %NULL, this function returns immediately for convenience.
479 *
480 * The convention within GIO is that cancelling an asynchronous
481 * operation causes it to complete asynchronously. That is, if you
482 * cancel the operation from the same thread in which it is running,
483 * then the operation's #GAsyncReadyCallback will not be invoked until
484 * the application returns to the main loop.
485 **/
486void
487g_cancellable_cancel (GCancellable *cancellable)
488{
489 GCancellablePrivate *priv;
490
491 if (cancellable == NULL || g_cancellable_is_cancelled (cancellable))
492 return;
493
494 priv = cancellable->priv;
495
496 g_mutex_lock (mutex: &cancellable_mutex);
497
498 if (g_atomic_int_get (&priv->cancelled))
499 {
500 g_mutex_unlock (mutex: &cancellable_mutex);
501 return;
502 }
503
504 g_atomic_int_set (&priv->cancelled, TRUE);
505 priv->cancelled_running = TRUE;
506
507 if (priv->wakeup)
508 GLIB_PRIVATE_CALL (g_wakeup_signal) (priv->wakeup);
509
510 g_mutex_unlock (mutex: &cancellable_mutex);
511
512 g_object_ref (cancellable);
513 g_signal_emit (instance: cancellable, signal_id: signals[CANCELLED], detail: 0);
514
515 g_mutex_lock (mutex: &cancellable_mutex);
516
517 priv->cancelled_running = FALSE;
518 if (priv->cancelled_running_waiting)
519 g_cond_broadcast (cond: &cancellable_cond);
520 priv->cancelled_running_waiting = FALSE;
521
522 g_mutex_unlock (mutex: &cancellable_mutex);
523
524 g_object_unref (object: cancellable);
525}
526
527/**
528 * g_cancellable_connect:
529 * @cancellable: A #GCancellable.
530 * @callback: The #GCallback to connect.
531 * @data: Data to pass to @callback.
532 * @data_destroy_func: (nullable): Free function for @data or %NULL.
533 *
534 * Convenience function to connect to the #GCancellable::cancelled
535 * signal. Also handles the race condition that may happen
536 * if the cancellable is cancelled right before connecting.
537 *
538 * @callback is called at most once, either directly at the
539 * time of the connect if @cancellable is already cancelled,
540 * or when @cancellable is cancelled in some thread.
541 *
542 * @data_destroy_func will be called when the handler is
543 * disconnected, or immediately if the cancellable is already
544 * cancelled.
545 *
546 * See #GCancellable::cancelled for details on how to use this.
547 *
548 * Since GLib 2.40, the lock protecting @cancellable is not held when
549 * @callback is invoked. This lifts a restriction in place for
550 * earlier GLib versions which now makes it easier to write cleanup
551 * code that unconditionally invokes e.g. g_cancellable_cancel().
552 *
553 * Returns: The id of the signal handler or 0 if @cancellable has already
554 * been cancelled.
555 *
556 * Since: 2.22
557 */
558gulong
559g_cancellable_connect (GCancellable *cancellable,
560 GCallback callback,
561 gpointer data,
562 GDestroyNotify data_destroy_func)
563{
564 gulong id;
565
566 g_return_val_if_fail (G_IS_CANCELLABLE (cancellable), 0);
567
568 g_mutex_lock (mutex: &cancellable_mutex);
569
570 if (g_atomic_int_get (&cancellable->priv->cancelled))
571 {
572 void (*_callback) (GCancellable *cancellable,
573 gpointer user_data);
574
575 g_mutex_unlock (mutex: &cancellable_mutex);
576
577 _callback = (void *)callback;
578 id = 0;
579
580 _callback (cancellable, data);
581
582 if (data_destroy_func)
583 data_destroy_func (data);
584 }
585 else
586 {
587 id = g_signal_connect_data (instance: cancellable, detailed_signal: "cancelled",
588 c_handler: callback, data,
589 destroy_data: (GClosureNotify) data_destroy_func,
590 connect_flags: 0);
591
592 g_mutex_unlock (mutex: &cancellable_mutex);
593 }
594
595
596 return id;
597}
598
599/**
600 * g_cancellable_disconnect:
601 * @cancellable: (nullable): A #GCancellable or %NULL.
602 * @handler_id: Handler id of the handler to be disconnected, or `0`.
603 *
604 * Disconnects a handler from a cancellable instance similar to
605 * g_signal_handler_disconnect(). Additionally, in the event that a
606 * signal handler is currently running, this call will block until the
607 * handler has finished. Calling this function from a
608 * #GCancellable::cancelled signal handler will therefore result in a
609 * deadlock.
610 *
611 * This avoids a race condition where a thread cancels at the
612 * same time as the cancellable operation is finished and the
613 * signal handler is removed. See #GCancellable::cancelled for
614 * details on how to use this.
615 *
616 * If @cancellable is %NULL or @handler_id is `0` this function does
617 * nothing.
618 *
619 * Since: 2.22
620 */
621void
622g_cancellable_disconnect (GCancellable *cancellable,
623 gulong handler_id)
624{
625 GCancellablePrivate *priv;
626
627 if (handler_id == 0 || cancellable == NULL)
628 return;
629
630 g_mutex_lock (mutex: &cancellable_mutex);
631
632 priv = cancellable->priv;
633
634 while (priv->cancelled_running)
635 {
636 priv->cancelled_running_waiting = TRUE;
637 g_cond_wait (cond: &cancellable_cond, mutex: &cancellable_mutex);
638 }
639
640 g_signal_handler_disconnect (instance: cancellable, handler_id);
641
642 g_mutex_unlock (mutex: &cancellable_mutex);
643}
644
645typedef struct {
646 GSource source;
647
648 GCancellable *cancellable;
649 gulong cancelled_handler;
650 /* Protected by cancellable_mutex: */
651 gboolean resurrected_during_cancellation;
652} GCancellableSource;
653
654/*
655 * The reference count of the GSource might be 0 at this point but it is not
656 * finalized yet and its dispose function did not run yet, or otherwise we
657 * would have disconnected the signal handler already and due to the signal
658 * emission lock it would be impossible to call the signal handler at that
659 * point. That is: at this point we either have a fully valid GSource, or
660 * it's not disposed or finalized yet and we can still resurrect it as needed.
661 *
662 * As such we first ensure that we have a strong reference to the GSource in
663 * here before calling any other GSource API.
664 */
665static void
666cancellable_source_cancelled (GCancellable *cancellable,
667 gpointer user_data)
668{
669 GSource *source = user_data;
670 GCancellableSource *cancellable_source = (GCancellableSource *) source;
671
672 g_mutex_lock (mutex: &cancellable_mutex);
673
674 /* Drop the reference added in cancellable_source_dispose(); see the comment there.
675 * The reference must be dropped after unlocking @cancellable_mutex since
676 * it could be the final reference, and the dispose function takes
677 * @cancellable_mutex. */
678 if (cancellable_source->resurrected_during_cancellation)
679 {
680 cancellable_source->resurrected_during_cancellation = FALSE;
681 g_mutex_unlock (mutex: &cancellable_mutex);
682 g_source_unref (source);
683 return;
684 }
685
686 g_source_ref (source);
687 g_mutex_unlock (mutex: &cancellable_mutex);
688 g_source_set_ready_time (source, ready_time: 0);
689 g_source_unref (source);
690}
691
692static gboolean
693cancellable_source_dispatch (GSource *source,
694 GSourceFunc callback,
695 gpointer user_data)
696{
697 GCancellableSourceFunc func = (GCancellableSourceFunc)callback;
698 GCancellableSource *cancellable_source = (GCancellableSource *)source;
699
700 g_source_set_ready_time (source, ready_time: -1);
701 return (*func) (cancellable_source->cancellable, user_data);
702}
703
704static void
705cancellable_source_dispose (GSource *source)
706{
707 GCancellableSource *cancellable_source = (GCancellableSource *)source;
708
709 g_mutex_lock (mutex: &cancellable_mutex);
710
711 if (cancellable_source->cancellable)
712 {
713 if (cancellable_source->cancellable->priv->cancelled_running)
714 {
715 /* There can be a race here: if thread A has called
716 * g_cancellable_cancel() and has got as far as committing to call
717 * cancellable_source_cancelled(), then thread B drops the final
718 * ref on the GCancellableSource before g_source_ref() is called in
719 * cancellable_source_cancelled(), then cancellable_source_dispose()
720 * will run through and the GCancellableSource will be finalised
721 * before cancellable_source_cancelled() gets to g_source_ref(). It
722 * will then be left in a state where it’s committed to using a
723 * dangling GCancellableSource pointer.
724 *
725 * Eliminate that race by resurrecting the #GSource temporarily, and
726 * then dropping that reference in cancellable_source_cancelled(),
727 * which should be guaranteed to fire because we’re inside a
728 * @cancelled_running block.
729 */
730 g_source_ref (source);
731 cancellable_source->resurrected_during_cancellation = TRUE;
732 }
733
734 g_clear_signal_handler (&cancellable_source->cancelled_handler,
735 cancellable_source->cancellable);
736 g_clear_object (&cancellable_source->cancellable);
737 }
738
739 g_mutex_unlock (mutex: &cancellable_mutex);
740}
741
742static gboolean
743cancellable_source_closure_callback (GCancellable *cancellable,
744 gpointer data)
745{
746 GClosure *closure = data;
747
748 GValue params = G_VALUE_INIT;
749 GValue result_value = G_VALUE_INIT;
750 gboolean result;
751
752 g_value_init (value: &result_value, G_TYPE_BOOLEAN);
753
754 g_value_init (value: &params, G_TYPE_CANCELLABLE);
755 g_value_set_object (value: &params, v_object: cancellable);
756
757 g_closure_invoke (closure, return_value: &result_value, n_param_values: 1, param_values: &params, NULL);
758
759 result = g_value_get_boolean (value: &result_value);
760 g_value_unset (value: &result_value);
761 g_value_unset (value: &params);
762
763 return result;
764}
765
766static GSourceFuncs cancellable_source_funcs =
767{
768 NULL,
769 NULL,
770 cancellable_source_dispatch,
771 NULL,
772 (GSourceFunc)cancellable_source_closure_callback,
773 NULL,
774};
775
776/**
777 * g_cancellable_source_new:
778 * @cancellable: (nullable): a #GCancellable, or %NULL
779 *
780 * Creates a source that triggers if @cancellable is cancelled and
781 * calls its callback of type #GCancellableSourceFunc. This is
782 * primarily useful for attaching to another (non-cancellable) source
783 * with g_source_add_child_source() to add cancellability to it.
784 *
785 * For convenience, you can call this with a %NULL #GCancellable,
786 * in which case the source will never trigger.
787 *
788 * The new #GSource will hold a reference to the #GCancellable.
789 *
790 * Returns: (transfer full): the new #GSource.
791 *
792 * Since: 2.28
793 */
794GSource *
795g_cancellable_source_new (GCancellable *cancellable)
796{
797 GSource *source;
798 GCancellableSource *cancellable_source;
799
800 source = g_source_new (source_funcs: &cancellable_source_funcs, struct_size: sizeof (GCancellableSource));
801 g_source_set_name (source, name: "GCancellable");
802 g_source_set_dispose_function (source, dispose: cancellable_source_dispose);
803 cancellable_source = (GCancellableSource *)source;
804
805 if (cancellable)
806 {
807 cancellable_source->cancellable = g_object_ref (cancellable);
808
809 /* We intentionally don't use g_cancellable_connect() here,
810 * because we don't want the "at most once" behavior.
811 */
812 cancellable_source->cancelled_handler =
813 g_signal_connect (cancellable, "cancelled",
814 G_CALLBACK (cancellable_source_cancelled),
815 source);
816 if (g_cancellable_is_cancelled (cancellable))
817 g_source_set_ready_time (source, ready_time: 0);
818 }
819
820 return source;
821}
822

source code of gtk/subprojects/glib/gio/gcancellable.c