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, write to the
17 * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
18 * Boston, MA 02111-1307, USA.
20 * Author: Alexander Larsson <alexl@redhat.com>
26 #include "glib-private.h"
27 #include "gcancellable.h"
32 * SECTION:gcancellable
33 * @short_description: Thread-safe Operation Cancellation Stack
36 * GCancellable is a thread-safe operation cancellation stack used
37 * throughout GIO to allow for cancellation of synchronous and
38 * asynchronous operations.
46 struct _GCancellablePrivate
49 guint cancelled_running_waiting : 1;
50 GThread *cancelled_running_thread;
56 static guint signals[LAST_SIGNAL] = { 0 };
58 G_DEFINE_TYPE_WITH_PRIVATE (GCancellable, g_cancellable, G_TYPE_OBJECT)
60 static GPrivate current_cancellable;
61 static GMutex cancellable_mutex;
62 static GCond cancellable_cond;
65 g_cancellable_finalize (GObject *object)
67 GCancellable *cancellable = G_CANCELLABLE (object);
69 if (cancellable->priv->wakeup)
70 GLIB_PRIVATE_CALL (g_wakeup_free) (cancellable->priv->wakeup);
72 G_OBJECT_CLASS (g_cancellable_parent_class)->finalize (object);
76 g_cancellable_class_init (GCancellableClass *klass)
78 GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
80 gobject_class->finalize = g_cancellable_finalize;
83 * GCancellable::cancelled:
84 * @cancellable: a #GCancellable.
86 * Emitted when the operation has been cancelled.
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.
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
96 * <emphasis>after</emphasis> a call to
97 * g_signal_handler_disconnect() for that handler has already
100 * There is also a problem when cancellation happen
101 * right before connecting to the signal. If this happens the
102 * signal will unexpectedly not be emitted, and checking before
103 * connecting to the signal leaves a race condition where this is
106 * In order to make it safe and easy to connect handlers there
107 * are two helper functions: g_cancellable_connect() and
108 * g_cancellable_disconnect() which protect against problems
111 * An example of how to us this:
113 * /<!-- -->* Make sure we don't do any unnecessary work if already cancelled *<!-- -->/
114 * if (g_cancellable_set_error_if_cancelled (cancellable))
117 * /<!-- -->* Set up all the data needed to be able to
118 * * handle cancellation of the operation *<!-- -->/
119 * my_data = my_data_new (...);
123 * id = g_cancellable_connect (cancellable,
124 * G_CALLBACK (cancelled_handler)
127 * /<!-- -->* cancellable operation here... *<!-- -->/
129 * g_cancellable_disconnect (cancellable, id);
131 * /<!-- -->* cancelled_handler is never called after this, it
132 * * is now safe to free the data *<!-- -->/
133 * my_data_free (my_data);
136 * Note that the cancelled signal is emitted in the thread that
137 * the user cancelled from, which may be the main thread. So, the
138 * cancellable signal should not do something that can block.
141 g_signal_new (I_("cancelled"),
142 G_TYPE_FROM_CLASS (gobject_class),
144 G_STRUCT_OFFSET (GCancellableClass, cancelled),
146 g_cclosure_marshal_VOID__VOID,
152 g_cancellable_init (GCancellable *cancellable)
154 cancellable->priv = g_cancellable_get_instance_private (cancellable);
160 * Creates a new #GCancellable object.
162 * Applications that want to start one or more operations
163 * that should be cancellable should create a #GCancellable
164 * and pass it to the operations.
166 * One #GCancellable can be used in multiple consecutive
167 * operations or in multiple concurrent operations.
169 * Returns: a #GCancellable.
172 g_cancellable_new (void)
174 return g_object_new (G_TYPE_CANCELLABLE, NULL);
178 * g_cancellable_push_current:
179 * @cancellable: a #GCancellable object
181 * Pushes @cancellable onto the cancellable stack. The current
182 * cancellable can then be received using g_cancellable_get_current().
184 * This is useful when implementing cancellable operations in
185 * code that does not allow you to pass down the cancellable object.
187 * This is typically called automatically by e.g. #GFile operations,
188 * so you rarely have to call this yourself.
191 g_cancellable_push_current (GCancellable *cancellable)
195 g_return_if_fail (cancellable != NULL);
197 l = g_private_get (¤t_cancellable);
198 l = g_slist_prepend (l, cancellable);
199 g_private_set (¤t_cancellable, l);
203 * g_cancellable_pop_current:
204 * @cancellable: a #GCancellable object
206 * Pops @cancellable off the cancellable stack (verifying that @cancellable
207 * is on the top of the stack).
210 g_cancellable_pop_current (GCancellable *cancellable)
214 l = g_private_get (¤t_cancellable);
216 g_return_if_fail (l != NULL);
217 g_return_if_fail (l->data == cancellable);
219 l = g_slist_delete_link (l, l);
220 g_private_set (¤t_cancellable, l);
224 * g_cancellable_get_current:
226 * Gets the top cancellable from the stack.
228 * Returns: (transfer none): a #GCancellable from the top of the stack, or %NULL
229 * if the stack is empty.
232 g_cancellable_get_current (void)
236 l = g_private_get (¤t_cancellable);
240 return G_CANCELLABLE (l->data);
244 * g_cancellable_reset:
245 * @cancellable: a #GCancellable object.
247 * Resets @cancellable to its uncancelled state.
249 * If cancellable is currently in use by any cancellable operation
250 * then the behavior of this function is undefined.
253 g_cancellable_reset (GCancellable *cancellable)
255 GCancellablePrivate *priv;
257 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
259 g_mutex_lock (&cancellable_mutex);
261 priv = cancellable->priv;
263 while (priv->cancelled_running_thread != NULL &&
264 priv->cancelled_running_thread != g_thread_self ())
266 priv->cancelled_running_waiting = TRUE;
267 g_cond_wait (&cancellable_cond, &cancellable_mutex);
273 GLIB_PRIVATE_CALL (g_wakeup_acknowledge) (priv->wakeup);
275 priv->cancelled = FALSE;
278 g_mutex_unlock (&cancellable_mutex);
282 * g_cancellable_is_cancelled:
283 * @cancellable: (allow-none): a #GCancellable or %NULL
285 * Checks if a cancellable job has been cancelled.
287 * Returns: %TRUE if @cancellable is cancelled,
288 * FALSE if called with %NULL or if item is not cancelled.
291 g_cancellable_is_cancelled (GCancellable *cancellable)
293 return cancellable != NULL && cancellable->priv->cancelled;
297 * g_cancellable_set_error_if_cancelled:
298 * @cancellable: (allow-none): a #GCancellable or %NULL
299 * @error: #GError to append error state to
301 * If the @cancellable is cancelled, sets the error to notify
302 * that the operation was cancelled.
304 * Returns: %TRUE if @cancellable was cancelled, %FALSE if it was not
307 g_cancellable_set_error_if_cancelled (GCancellable *cancellable,
310 if (g_cancellable_is_cancelled (cancellable))
312 g_set_error_literal (error,
314 G_IO_ERROR_CANCELLED,
315 _("Operation was cancelled"));
323 * g_cancellable_get_fd:
324 * @cancellable: a #GCancellable.
326 * Gets the file descriptor for a cancellable job. This can be used to
327 * implement cancellable operations on Unix systems. The returned fd will
328 * turn readable when @cancellable is cancelled.
330 * You are not supposed to read from the fd yourself, just check for
331 * readable status. Reading to unset the readable status is done
332 * with g_cancellable_reset().
334 * After a successful return from this function, you should use
335 * g_cancellable_release_fd() to free up resources allocated for
336 * the returned file descriptor.
338 * See also g_cancellable_make_pollfd().
340 * Returns: A valid file descriptor. %-1 if the file descriptor
341 * is not supported, or on errors.
344 g_cancellable_get_fd (GCancellable *cancellable)
348 if (cancellable == NULL)
354 g_cancellable_make_pollfd (cancellable, &pollfd);
361 * g_cancellable_make_pollfd:
362 * @cancellable: (allow-none): a #GCancellable or %NULL
363 * @pollfd: a pointer to a #GPollFD
365 * Creates a #GPollFD corresponding to @cancellable; this can be passed
366 * to g_poll() and used to poll for cancellation. This is useful both
367 * for unix systems without a native poll and for portability to
370 * When this function returns %TRUE, you should use
371 * g_cancellable_release_fd() to free up resources allocated for the
372 * @pollfd. After a %FALSE return, do not call g_cancellable_release_fd().
374 * If this function returns %FALSE, either no @cancellable was given or
375 * resource limits prevent this function from allocating the necessary
376 * structures for polling. (On Linux, you will likely have reached
377 * the maximum number of file descriptors.) The suggested way to handle
378 * these cases is to ignore the @cancellable.
380 * You are not supposed to read from the fd yourself, just check for
381 * readable status. Reading to unset the readable status is done
382 * with g_cancellable_reset().
384 * Returns: %TRUE if @pollfd was successfully initialized, %FALSE on
385 * failure to prepare the cancellable.
390 g_cancellable_make_pollfd (GCancellable *cancellable, GPollFD *pollfd)
392 g_return_val_if_fail (pollfd != NULL, FALSE);
393 if (cancellable == NULL)
395 g_return_val_if_fail (G_IS_CANCELLABLE (cancellable), FALSE);
397 g_mutex_lock (&cancellable_mutex);
399 cancellable->priv->fd_refcount++;
401 if (cancellable->priv->wakeup == NULL)
403 cancellable->priv->wakeup = GLIB_PRIVATE_CALL (g_wakeup_new) ();
405 if (cancellable->priv->cancelled)
406 GLIB_PRIVATE_CALL (g_wakeup_signal) (cancellable->priv->wakeup);
409 GLIB_PRIVATE_CALL (g_wakeup_get_pollfd) (cancellable->priv->wakeup, pollfd);
411 g_mutex_unlock (&cancellable_mutex);
417 * g_cancellable_release_fd:
418 * @cancellable: a #GCancellable
420 * Releases a resources previously allocated by g_cancellable_get_fd()
421 * or g_cancellable_make_pollfd().
423 * For compatibility reasons with older releases, calling this function
424 * is not strictly required, the resources will be automatically freed
425 * when the @cancellable is finalized. However, the @cancellable will
426 * block scarce file descriptors until it is finalized if this function
427 * is not called. This can cause the application to run out of file
428 * descriptors when many #GCancellables are used at the same time.
433 g_cancellable_release_fd (GCancellable *cancellable)
435 GCancellablePrivate *priv;
437 if (cancellable == NULL)
440 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
441 g_return_if_fail (cancellable->priv->fd_refcount > 0);
443 priv = cancellable->priv;
445 g_mutex_lock (&cancellable_mutex);
448 if (priv->fd_refcount == 0)
450 GLIB_PRIVATE_CALL (g_wakeup_free) (priv->wakeup);
454 g_mutex_unlock (&cancellable_mutex);
458 * g_cancellable_cancel:
459 * @cancellable: a #GCancellable object.
461 * Will set @cancellable to cancelled, and will emit the
462 * #GCancellable::cancelled signal. (However, see the warning about
463 * race conditions in the documentation for that signal if you are
464 * planning to connect to it.)
466 * This function is thread-safe. In other words, you can safely call
467 * it from a thread other than the one running the operation that was
468 * passed the @cancellable.
470 * The convention within gio is that cancelling an asynchronous
471 * operation causes it to complete asynchronously. That is, if you
472 * cancel the operation from the same thread in which it is running,
473 * then the operation's #GAsyncReadyCallback will not be invoked until
474 * the application returns to the main loop.
477 g_cancellable_cancel (GCancellable *cancellable)
479 GCancellablePrivate *priv;
481 if (cancellable == NULL ||
482 cancellable->priv->cancelled)
485 priv = cancellable->priv;
487 g_mutex_lock (&cancellable_mutex);
491 g_mutex_unlock (&cancellable_mutex);
495 priv->cancelled = TRUE;
496 priv->cancelled_running_thread = g_thread_self ();
499 GLIB_PRIVATE_CALL (g_wakeup_signal) (priv->wakeup);
501 g_mutex_unlock (&cancellable_mutex);
503 g_object_ref (cancellable);
504 g_signal_emit (cancellable, signals[CANCELLED], 0);
506 g_mutex_lock (&cancellable_mutex);
508 priv->cancelled_running_thread = NULL;
509 if (priv->cancelled_running_waiting)
510 g_cond_broadcast (&cancellable_cond);
511 priv->cancelled_running_waiting = FALSE;
513 g_mutex_unlock (&cancellable_mutex);
515 g_object_unref (cancellable);
519 * g_cancellable_connect:
520 * @cancellable: A #GCancellable.
521 * @callback: The #GCallback to connect.
522 * @data: Data to pass to @callback.
523 * @data_destroy_func: (allow-none): Free function for @data or %NULL.
525 * Convenience function to connect to the #GCancellable::cancelled
526 * signal. Also handles the race condition that may happen
527 * if the cancellable is cancelled right before connecting.
529 * @callback is called at most once, either directly at the
530 * time of the connect if @cancellable is already cancelled,
531 * or when @cancellable is cancelled in some thread.
533 * @data_destroy_func will be called when the handler is
534 * disconnected, or immediately if the cancellable is already
537 * See #GCancellable::cancelled for details on how to use this.
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 on a different thread, this
593 * call will block until the handler has finished.
595 * This avoids a race condition where a thread cancels at the
596 * same time as the cancellable operation is finished and the
597 * signal handler is removed. See #GCancellable::cancelled for
598 * details on how to use this.
600 * Note, since 2.38 it is safe to call this function from a
601 * #GCancellable::cancelled signal handler, something which would
602 * previously have caused a deadlock. However, it is not a good idea
603 * to disconnect a signal handler from inside its *own* signal handler.
605 * If @cancellable is %NULL or @handler_id is %0 this function does
611 g_cancellable_disconnect (GCancellable *cancellable,
614 GCancellablePrivate *priv;
616 if (handler_id == 0 || cancellable == NULL)
619 g_mutex_lock (&cancellable_mutex);
621 priv = cancellable->priv;
623 while (priv->cancelled_running_thread != NULL &&
624 priv->cancelled_running_thread != g_thread_self ())
626 priv->cancelled_running_waiting = TRUE;
627 g_cond_wait (&cancellable_cond, &cancellable_mutex);
630 g_signal_handler_disconnect (cancellable, handler_id);
632 g_mutex_unlock (&cancellable_mutex);
638 GCancellable *cancellable;
639 guint cancelled_handler;
640 } GCancellableSource;
643 cancellable_source_cancelled (GCancellable *cancellable,
646 GSource *source = user_data;
648 if (!g_source_is_destroyed (source))
649 g_source_set_ready_time (source, 0);
653 cancellable_source_dispatch (GSource *source,
654 GSourceFunc callback,
657 GCancellableSourceFunc func = (GCancellableSourceFunc)callback;
658 GCancellableSource *cancellable_source = (GCancellableSource *)source;
660 g_source_set_ready_time (source, -1);
661 return (*func) (cancellable_source->cancellable, user_data);
665 cancellable_source_finalize (GSource *source)
667 GCancellableSource *cancellable_source = (GCancellableSource *)source;
669 if (cancellable_source->cancellable)
671 g_cancellable_disconnect (cancellable_source->cancellable,
672 cancellable_source->cancelled_handler);
673 g_object_unref (cancellable_source->cancellable);
678 cancellable_source_closure_callback (GCancellable *cancellable,
681 GClosure *closure = data;
683 GValue params = G_VALUE_INIT;
684 GValue result_value = G_VALUE_INIT;
687 g_value_init (&result_value, G_TYPE_BOOLEAN);
689 g_value_init (¶ms, G_TYPE_CANCELLABLE);
690 g_value_set_object (¶ms, cancellable);
692 g_closure_invoke (closure, &result_value, 1, ¶ms, NULL);
694 result = g_value_get_boolean (&result_value);
695 g_value_unset (&result_value);
696 g_value_unset (¶ms);
701 static GSourceFuncs cancellable_source_funcs =
705 cancellable_source_dispatch,
706 cancellable_source_finalize,
707 (GSourceFunc)cancellable_source_closure_callback,
711 * g_cancellable_source_new: (skip)
712 * @cancellable: (allow-none): a #GCancellable, or %NULL
714 * Creates a source that triggers if @cancellable is cancelled and
715 * calls its callback of type #GCancellableSourceFunc. This is
716 * primarily useful for attaching to another (non-cancellable) source
717 * with g_source_add_child_source() to add cancellability to it.
719 * For convenience, you can call this with a %NULL #GCancellable,
720 * in which case the source will never trigger.
722 * Return value: (transfer full): the new #GSource.
727 g_cancellable_source_new (GCancellable *cancellable)
730 GCancellableSource *cancellable_source;
732 source = g_source_new (&cancellable_source_funcs, sizeof (GCancellableSource));
733 g_source_set_name (source, "GCancellable");
734 cancellable_source = (GCancellableSource *)source;
738 cancellable_source->cancellable = g_object_ref (cancellable);
739 cancellable_source->cancelled_handler =
740 g_cancellable_connect (cancellable,
741 G_CALLBACK (cancellable_source_cancelled),