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>
24 #include "glib-private.h"
25 #include "gcancellable.h"
30 * SECTION:gcancellable
31 * @short_description: Thread-safe Operation Cancellation Stack
34 * GCancellable is a thread-safe operation cancellation stack used
35 * throughout GIO to allow for cancellation of synchronous and
36 * asynchronous operations.
44 struct _GCancellablePrivate
47 guint cancelled_running : 1;
48 guint cancelled_running_waiting : 1;
54 static guint signals[LAST_SIGNAL] = { 0 };
56 G_DEFINE_TYPE_WITH_PRIVATE (GCancellable, g_cancellable, G_TYPE_OBJECT)
58 static GPrivate current_cancellable;
59 static GMutex cancellable_mutex;
60 static GCond cancellable_cond;
63 g_cancellable_finalize (GObject *object)
65 GCancellable *cancellable = G_CANCELLABLE (object);
67 if (cancellable->priv->wakeup)
68 GLIB_PRIVATE_CALL (g_wakeup_free) (cancellable->priv->wakeup);
70 G_OBJECT_CLASS (g_cancellable_parent_class)->finalize (object);
74 g_cancellable_class_init (GCancellableClass *klass)
76 GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
78 gobject_class->finalize = g_cancellable_finalize;
81 * GCancellable::cancelled:
82 * @cancellable: a #GCancellable.
84 * Emitted when the operation has been cancelled.
86 * Can be used by implementations of cancellable operations. If the
87 * operation is cancelled from another thread, the signal will be
88 * emitted in the thread that cancelled the operation, not the
89 * thread that is running the operation.
91 * Note that disconnecting from this signal (or any signal) in a
92 * multi-threaded program is prone to race conditions. For instance
93 * it is possible that a signal handler may be invoked even after
94 * a call to g_signal_handler_disconnect() for that handler has
97 * There is also a problem when cancellation happens right before
98 * connecting to the signal. If this happens the signal will
99 * unexpectedly not be emitted, and checking before connecting to
100 * the signal leaves a race condition where this is still happening.
102 * In order to make it safe and easy to connect handlers there
103 * are two helper functions: g_cancellable_connect() and
104 * g_cancellable_disconnect() which protect against problems
107 * An example of how to us this:
108 * |[<!-- language="C" -->
109 * // Make sure we don't do unnecessary work if already cancelled
110 * if (g_cancellable_set_error_if_cancelled (cancellable, error))
113 * // Set up all the data needed to be able to handle cancellation
114 * // of the operation
115 * my_data = my_data_new (...);
119 * id = g_cancellable_connect (cancellable,
120 * G_CALLBACK (cancelled_handler)
123 * // cancellable operation here...
125 * g_cancellable_disconnect (cancellable, id);
127 * // cancelled_handler is never called after this, it is now safe
128 * // to free the data
129 * my_data_free (my_data);
132 * Note that the cancelled signal is emitted in the thread that
133 * the user cancelled from, which may be the main thread. So, the
134 * cancellable signal should not do something that can block.
137 g_signal_new (I_("cancelled"),
138 G_TYPE_FROM_CLASS (gobject_class),
140 G_STRUCT_OFFSET (GCancellableClass, cancelled),
142 g_cclosure_marshal_VOID__VOID,
148 g_cancellable_init (GCancellable *cancellable)
150 cancellable->priv = g_cancellable_get_instance_private (cancellable);
156 * Creates a new #GCancellable object.
158 * Applications that want to start one or more operations
159 * that should be cancellable should create a #GCancellable
160 * and pass it to the operations.
162 * One #GCancellable can be used in multiple consecutive
163 * operations or in multiple concurrent operations.
165 * Returns: a #GCancellable.
168 g_cancellable_new (void)
170 return g_object_new (G_TYPE_CANCELLABLE, NULL);
174 * g_cancellable_push_current:
175 * @cancellable: a #GCancellable object
177 * Pushes @cancellable onto the cancellable stack. The current
178 * cancellable can then be received using g_cancellable_get_current().
180 * This is useful when implementing cancellable operations in
181 * code that does not allow you to pass down the cancellable object.
183 * This is typically called automatically by e.g. #GFile operations,
184 * so you rarely have to call this yourself.
187 g_cancellable_push_current (GCancellable *cancellable)
191 g_return_if_fail (cancellable != NULL);
193 l = g_private_get (¤t_cancellable);
194 l = g_slist_prepend (l, cancellable);
195 g_private_set (¤t_cancellable, l);
199 * g_cancellable_pop_current:
200 * @cancellable: a #GCancellable object
202 * Pops @cancellable off the cancellable stack (verifying that @cancellable
203 * is on the top of the stack).
206 g_cancellable_pop_current (GCancellable *cancellable)
210 l = g_private_get (¤t_cancellable);
212 g_return_if_fail (l != NULL);
213 g_return_if_fail (l->data == cancellable);
215 l = g_slist_delete_link (l, l);
216 g_private_set (¤t_cancellable, l);
220 * g_cancellable_get_current:
222 * Gets the top cancellable from the stack.
224 * Returns: (nullable) (transfer none): a #GCancellable from the top
225 * of the stack, or %NULL if the stack is empty.
228 g_cancellable_get_current (void)
232 l = g_private_get (¤t_cancellable);
236 return G_CANCELLABLE (l->data);
240 * g_cancellable_reset:
241 * @cancellable: a #GCancellable object.
243 * Resets @cancellable to its uncancelled state.
245 * If cancellable is currently in use by any cancellable operation
246 * then the behavior of this function is undefined.
249 g_cancellable_reset (GCancellable *cancellable)
251 GCancellablePrivate *priv;
253 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
255 g_mutex_lock (&cancellable_mutex);
257 priv = cancellable->priv;
259 while (priv->cancelled_running)
261 priv->cancelled_running_waiting = TRUE;
262 g_cond_wait (&cancellable_cond, &cancellable_mutex);
268 GLIB_PRIVATE_CALL (g_wakeup_acknowledge) (priv->wakeup);
270 priv->cancelled = FALSE;
273 g_mutex_unlock (&cancellable_mutex);
277 * g_cancellable_is_cancelled:
278 * @cancellable: (allow-none): a #GCancellable or %NULL
280 * Checks if a cancellable job has been cancelled.
282 * Returns: %TRUE if @cancellable is cancelled,
283 * FALSE if called with %NULL or if item is not cancelled.
286 g_cancellable_is_cancelled (GCancellable *cancellable)
288 return cancellable != NULL && cancellable->priv->cancelled;
292 * g_cancellable_set_error_if_cancelled:
293 * @cancellable: (allow-none): a #GCancellable or %NULL
294 * @error: #GError to append error state to
296 * If the @cancellable is cancelled, sets the error to notify
297 * that the operation was cancelled.
299 * Returns: %TRUE if @cancellable was cancelled, %FALSE if it was not
302 g_cancellable_set_error_if_cancelled (GCancellable *cancellable,
305 if (g_cancellable_is_cancelled (cancellable))
307 g_set_error_literal (error,
309 G_IO_ERROR_CANCELLED,
310 _("Operation was cancelled"));
318 * g_cancellable_get_fd:
319 * @cancellable: a #GCancellable.
321 * Gets the file descriptor for a cancellable job. This can be used to
322 * implement cancellable operations on Unix systems. The returned fd will
323 * turn readable when @cancellable is cancelled.
325 * You are not supposed to read from the fd yourself, just check for
326 * readable status. Reading to unset the readable status is done
327 * with g_cancellable_reset().
329 * After a successful return from this function, you should use
330 * g_cancellable_release_fd() to free up resources allocated for
331 * the returned file descriptor.
333 * See also g_cancellable_make_pollfd().
335 * Returns: A valid file descriptor. %-1 if the file descriptor
336 * is not supported, or on errors.
339 g_cancellable_get_fd (GCancellable *cancellable)
343 if (cancellable == NULL)
349 g_cancellable_make_pollfd (cancellable, &pollfd);
356 * g_cancellable_make_pollfd:
357 * @cancellable: (allow-none): a #GCancellable or %NULL
358 * @pollfd: a pointer to a #GPollFD
360 * Creates a #GPollFD corresponding to @cancellable; this can be passed
361 * to g_poll() and used to poll for cancellation. This is useful both
362 * for unix systems without a native poll and for portability to
365 * When this function returns %TRUE, you should use
366 * g_cancellable_release_fd() to free up resources allocated for the
367 * @pollfd. After a %FALSE return, do not call g_cancellable_release_fd().
369 * If this function returns %FALSE, either no @cancellable was given or
370 * resource limits prevent this function from allocating the necessary
371 * structures for polling. (On Linux, you will likely have reached
372 * the maximum number of file descriptors.) The suggested way to handle
373 * these cases is to ignore the @cancellable.
375 * You are not supposed to read from the fd yourself, just check for
376 * readable status. Reading to unset the readable status is done
377 * with g_cancellable_reset().
379 * Returns: %TRUE if @pollfd was successfully initialized, %FALSE on
380 * failure to prepare the cancellable.
385 g_cancellable_make_pollfd (GCancellable *cancellable, GPollFD *pollfd)
387 g_return_val_if_fail (pollfd != NULL, FALSE);
388 if (cancellable == NULL)
390 g_return_val_if_fail (G_IS_CANCELLABLE (cancellable), FALSE);
392 g_mutex_lock (&cancellable_mutex);
394 cancellable->priv->fd_refcount++;
396 if (cancellable->priv->wakeup == NULL)
398 cancellable->priv->wakeup = GLIB_PRIVATE_CALL (g_wakeup_new) ();
400 if (cancellable->priv->cancelled)
401 GLIB_PRIVATE_CALL (g_wakeup_signal) (cancellable->priv->wakeup);
404 GLIB_PRIVATE_CALL (g_wakeup_get_pollfd) (cancellable->priv->wakeup, pollfd);
406 g_mutex_unlock (&cancellable_mutex);
412 * g_cancellable_release_fd:
413 * @cancellable: a #GCancellable
415 * Releases a resources previously allocated by g_cancellable_get_fd()
416 * or g_cancellable_make_pollfd().
418 * For compatibility reasons with older releases, calling this function
419 * is not strictly required, the resources will be automatically freed
420 * when the @cancellable is finalized. However, the @cancellable will
421 * block scarce file descriptors until it is finalized if this function
422 * is not called. This can cause the application to run out of file
423 * descriptors when many #GCancellables are used at the same time.
428 g_cancellable_release_fd (GCancellable *cancellable)
430 GCancellablePrivate *priv;
432 if (cancellable == NULL)
435 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
436 g_return_if_fail (cancellable->priv->fd_refcount > 0);
438 priv = cancellable->priv;
440 g_mutex_lock (&cancellable_mutex);
443 if (priv->fd_refcount == 0)
445 GLIB_PRIVATE_CALL (g_wakeup_free) (priv->wakeup);
449 g_mutex_unlock (&cancellable_mutex);
453 * g_cancellable_cancel:
454 * @cancellable: a #GCancellable object.
456 * Will set @cancellable to cancelled, and will emit the
457 * #GCancellable::cancelled signal. (However, see the warning about
458 * race conditions in the documentation for that signal if you are
459 * planning to connect to it.)
461 * This function is thread-safe. In other words, you can safely call
462 * it from a thread other than the one running the operation that was
463 * passed the @cancellable.
465 * The convention within gio is that cancelling an asynchronous
466 * operation causes it to complete asynchronously. That is, if you
467 * cancel the operation from the same thread in which it is running,
468 * then the operation's #GAsyncReadyCallback will not be invoked until
469 * the application returns to the main loop.
472 g_cancellable_cancel (GCancellable *cancellable)
474 GCancellablePrivate *priv;
476 if (cancellable == NULL ||
477 cancellable->priv->cancelled)
480 priv = cancellable->priv;
482 g_mutex_lock (&cancellable_mutex);
486 g_mutex_unlock (&cancellable_mutex);
490 priv->cancelled = TRUE;
491 priv->cancelled_running = TRUE;
494 GLIB_PRIVATE_CALL (g_wakeup_signal) (priv->wakeup);
496 g_mutex_unlock (&cancellable_mutex);
498 g_object_ref (cancellable);
499 g_signal_emit (cancellable, signals[CANCELLED], 0);
501 g_mutex_lock (&cancellable_mutex);
503 priv->cancelled_running = FALSE;
504 if (priv->cancelled_running_waiting)
505 g_cond_broadcast (&cancellable_cond);
506 priv->cancelled_running_waiting = FALSE;
508 g_mutex_unlock (&cancellable_mutex);
510 g_object_unref (cancellable);
514 * g_cancellable_connect:
515 * @cancellable: A #GCancellable.
516 * @callback: The #GCallback to connect.
517 * @data: Data to pass to @callback.
518 * @data_destroy_func: (allow-none): Free function for @data or %NULL.
520 * Convenience function to connect to the #GCancellable::cancelled
521 * signal. Also handles the race condition that may happen
522 * if the cancellable is cancelled right before connecting.
524 * @callback is called at most once, either directly at the
525 * time of the connect if @cancellable is already cancelled,
526 * or when @cancellable is cancelled in some thread.
528 * @data_destroy_func will be called when the handler is
529 * disconnected, or immediately if the cancellable is already
532 * See #GCancellable::cancelled for details on how to use this.
534 * Since GLib 2.40, the lock protecting @cancellable is not held when
535 * @callback is invoked. This lifts a restriction in place for
536 * earlier GLib versions which now makes it easier to write cleanup
537 * code that unconditionally invokes e.g. g_cancellable_cancel().
539 * Returns: The id of the signal handler or 0 if @cancellable has already
545 g_cancellable_connect (GCancellable *cancellable,
548 GDestroyNotify data_destroy_func)
552 g_return_val_if_fail (G_IS_CANCELLABLE (cancellable), 0);
554 g_mutex_lock (&cancellable_mutex);
556 if (cancellable->priv->cancelled)
558 void (*_callback) (GCancellable *cancellable,
561 g_mutex_unlock (&cancellable_mutex);
563 _callback = (void *)callback;
566 _callback (cancellable, data);
568 if (data_destroy_func)
569 data_destroy_func (data);
573 id = g_signal_connect_data (cancellable, "cancelled",
575 (GClosureNotify) data_destroy_func,
578 g_mutex_unlock (&cancellable_mutex);
586 * g_cancellable_disconnect:
587 * @cancellable: (allow-none): A #GCancellable or %NULL.
588 * @handler_id: Handler id of the handler to be disconnected, or %0.
590 * Disconnects a handler from a cancellable instance similar to
591 * g_signal_handler_disconnect(). Additionally, in the event that a
592 * signal handler is currently running, this call will block until the
593 * handler has finished. Calling this function from a
594 * #GCancellable::cancelled signal handler will therefore result in a
597 * This avoids a race condition where a thread cancels at the
598 * same time as the cancellable operation is finished and the
599 * signal handler is removed. See #GCancellable::cancelled for
600 * details on how to use this.
602 * If @cancellable is %NULL or @handler_id is %0 this function does
608 g_cancellable_disconnect (GCancellable *cancellable,
611 GCancellablePrivate *priv;
613 if (handler_id == 0 || cancellable == NULL)
616 g_mutex_lock (&cancellable_mutex);
618 priv = cancellable->priv;
620 while (priv->cancelled_running)
622 priv->cancelled_running_waiting = TRUE;
623 g_cond_wait (&cancellable_cond, &cancellable_mutex);
626 g_signal_handler_disconnect (cancellable, handler_id);
628 g_mutex_unlock (&cancellable_mutex);
634 GCancellable *cancellable;
635 guint cancelled_handler;
636 } GCancellableSource;
639 cancellable_source_cancelled (GCancellable *cancellable,
642 GSource *source = user_data;
644 if (!g_source_is_destroyed (source))
645 g_source_set_ready_time (source, 0);
649 cancellable_source_dispatch (GSource *source,
650 GSourceFunc callback,
653 GCancellableSourceFunc func = (GCancellableSourceFunc)callback;
654 GCancellableSource *cancellable_source = (GCancellableSource *)source;
656 g_source_set_ready_time (source, -1);
657 return (*func) (cancellable_source->cancellable, user_data);
661 cancellable_source_finalize (GSource *source)
663 GCancellableSource *cancellable_source = (GCancellableSource *)source;
665 if (cancellable_source->cancellable)
667 g_cancellable_disconnect (cancellable_source->cancellable,
668 cancellable_source->cancelled_handler);
669 g_object_unref (cancellable_source->cancellable);
674 cancellable_source_closure_callback (GCancellable *cancellable,
677 GClosure *closure = data;
679 GValue params = G_VALUE_INIT;
680 GValue result_value = G_VALUE_INIT;
683 g_value_init (&result_value, G_TYPE_BOOLEAN);
685 g_value_init (¶ms, G_TYPE_CANCELLABLE);
686 g_value_set_object (¶ms, cancellable);
688 g_closure_invoke (closure, &result_value, 1, ¶ms, NULL);
690 result = g_value_get_boolean (&result_value);
691 g_value_unset (&result_value);
692 g_value_unset (¶ms);
697 static GSourceFuncs cancellable_source_funcs =
701 cancellable_source_dispatch,
702 cancellable_source_finalize,
703 (GSourceFunc)cancellable_source_closure_callback,
707 * g_cancellable_source_new: (skip)
708 * @cancellable: (allow-none): a #GCancellable, or %NULL
710 * Creates a source that triggers if @cancellable is cancelled and
711 * calls its callback of type #GCancellableSourceFunc. This is
712 * primarily useful for attaching to another (non-cancellable) source
713 * with g_source_add_child_source() to add cancellability to it.
715 * For convenience, you can call this with a %NULL #GCancellable,
716 * in which case the source will never trigger.
718 * Returns: (transfer full): the new #GSource.
723 g_cancellable_source_new (GCancellable *cancellable)
726 GCancellableSource *cancellable_source;
728 source = g_source_new (&cancellable_source_funcs, sizeof (GCancellableSource));
729 g_source_set_name (source, "GCancellable");
730 cancellable_source = (GCancellableSource *)source;
734 cancellable_source->cancellable = g_object_ref (cancellable);
736 /* We intentionally don't use g_cancellable_connect() here,
737 * because we don't want the "at most once" behavior.
739 cancellable_source->cancelled_handler =
740 g_signal_connect (cancellable, "cancelled",
741 G_CALLBACK (cancellable_source_cancelled),
743 if (g_cancellable_is_cancelled (cancellable))
744 g_source_set_ready_time (source, 0);