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-unix.h"
34 #include "gcancellable.h"
35 #include "gio-marshal.h"
40 * SECTION:gcancellable
41 * @short_description: Thread-safe Operation Cancellation Stack
44 * GCancellable is a thread-safe operation cancellation stack used
45 * throughout GIO to allow for cancellation of synchronous and
46 * asynchronous operations.
54 struct _GCancellablePrivate
57 guint cancelled_running : 1;
58 guint cancelled_running_waiting : 1;
68 static guint signals[LAST_SIGNAL] = { 0 };
70 G_DEFINE_TYPE (GCancellable, g_cancellable, G_TYPE_OBJECT);
72 static GStaticPrivate current_cancellable = G_STATIC_PRIVATE_INIT;
73 G_LOCK_DEFINE_STATIC(cancellable);
74 static GCond *cancellable_cond = NULL;
77 g_cancellable_close_pipe (GCancellable *cancellable)
79 GCancellablePrivate *priv;
81 priv = cancellable->priv;
83 if (priv->cancel_pipe[0] != -1)
85 close (priv->cancel_pipe[0]);
86 priv->cancel_pipe[0] = -1;
89 if (priv->cancel_pipe[1] != -1)
91 close (priv->cancel_pipe[1]);
92 priv->cancel_pipe[1] = -1;
98 CloseHandle (priv->event);
105 g_cancellable_finalize (GObject *object)
107 GCancellable *cancellable = G_CANCELLABLE (object);
109 g_cancellable_close_pipe (cancellable);
111 G_OBJECT_CLASS (g_cancellable_parent_class)->finalize (object);
115 g_cancellable_class_init (GCancellableClass *klass)
117 GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
119 g_type_class_add_private (klass, sizeof (GCancellablePrivate));
121 if (cancellable_cond == NULL && g_thread_supported ())
122 cancellable_cond = g_cond_new ();
124 gobject_class->finalize = g_cancellable_finalize;
127 * GCancellable::cancelled:
128 * @cancellable: a #GCancellable.
130 * Emitted when the operation has been cancelled.
132 * Can be used by implementations of cancellable operations. If the
133 * operation is cancelled from another thread, the signal will be
134 * emitted in the thread that cancelled the operation, not the
135 * thread that is running the operation.
137 * Note that disconnecting from this signal (or any signal) in a
138 * multi-threaded program is prone to race conditions. For instance
139 * it is possible that a signal handler may be invoked even
140 * <emphasis>after</emphasis> a call to
141 * g_signal_handler_disconnect() for that handler has already
144 * There is also a problem when cancellation happen
145 * right before connecting to the signal. If this happens the
146 * signal will unexpectedly not be emitted, and checking before
147 * connecting to the signal leaves a race condition where this is
150 * In order to make it safe and easy to connect handlers there
151 * are two helper functions: g_cancellable_connect() and
152 * g_cancellable_disconnect() which protect against problems
155 * An example of how to us this:
157 * /<!-- -->* Make sure we don't do any unnecessary work if already cancelled *<!-- -->/
158 * if (g_cancellable_set_error_if_cancelled (cancellable))
161 * /<!-- -->* Set up all the data needed to be able to
162 * * handle cancellation of the operation *<!-- -->/
163 * my_data = my_data_new (...);
167 * id = g_cancellable_connect (cancellable,
168 * G_CALLBACK (cancelled_handler)
171 * /<!-- -->* cancellable operation here... *<!-- -->/
173 * g_cancellable_disconnect (cancellable, id);
175 * /<!-- -->* cancelled_handler is never called after this, it
176 * * is now safe to free the data *<!-- -->/
177 * my_data_free (my_data);
180 * Note that the cancelled signal is emitted in the thread that
181 * the user cancelled from, which may be the main thread. So, the
182 * cancellable signal should not do something that can block.
185 g_signal_new (I_("cancelled"),
186 G_TYPE_FROM_CLASS (gobject_class),
188 G_STRUCT_OFFSET (GCancellableClass, cancelled),
190 g_cclosure_marshal_VOID__VOID,
198 g_cancellable_open_pipe (GCancellable *cancellable)
200 GCancellablePrivate *priv;
202 priv = cancellable->priv;
203 if (g_unix_open_pipe (priv->cancel_pipe, FD_CLOEXEC, NULL))
205 /* Make them nonblocking, just to be sure we don't block
206 * on errors and stuff
208 g_unix_set_fd_nonblocking (priv->cancel_pipe[0], TRUE, NULL);
209 g_unix_set_fd_nonblocking (priv->cancel_pipe[1], TRUE, NULL);
217 c = write (priv->cancel_pipe[1], &ch, 1);
218 while (c == -1 && errno == EINTR);
225 g_cancellable_init (GCancellable *cancellable)
227 cancellable->priv = G_TYPE_INSTANCE_GET_PRIVATE (cancellable,
229 GCancellablePrivate);
230 cancellable->priv->cancel_pipe[0] = -1;
231 cancellable->priv->cancel_pipe[1] = -1;
237 * Creates a new #GCancellable object.
239 * Applications that want to start one or more operations
240 * that should be cancellable should create a #GCancellable
241 * and pass it to the operations.
243 * One #GCancellable can be used in multiple consecutive
244 * operations, but not in multiple concurrent operations.
246 * Returns: a #GCancellable.
249 g_cancellable_new (void)
251 return g_object_new (G_TYPE_CANCELLABLE, NULL);
255 * g_cancellable_push_current:
256 * @cancellable: a #GCancellable object
258 * Pushes @cancellable onto the cancellable stack. The current
259 * cancellable can then be recieved using g_cancellable_get_current().
261 * This is useful when implementing cancellable operations in
262 * code that does not allow you to pass down the cancellable object.
264 * This is typically called automatically by e.g. #GFile operations,
265 * so you rarely have to call this yourself.
268 g_cancellable_push_current (GCancellable *cancellable)
272 g_return_if_fail (cancellable != NULL);
274 l = g_static_private_get (¤t_cancellable);
275 l = g_slist_prepend (l, cancellable);
276 g_static_private_set (¤t_cancellable, l, NULL);
280 * g_cancellable_pop_current:
281 * @cancellable: a #GCancellable object
283 * Pops @cancellable off the cancellable stack (verifying that @cancellable
284 * is on the top of the stack).
287 g_cancellable_pop_current (GCancellable *cancellable)
291 l = g_static_private_get (¤t_cancellable);
293 g_return_if_fail (l != NULL);
294 g_return_if_fail (l->data == cancellable);
296 l = g_slist_delete_link (l, l);
297 g_static_private_set (¤t_cancellable, l, NULL);
301 * g_cancellable_get_current:
303 * Gets the top cancellable from the stack.
305 * Returns: (transfer none): a #GCancellable from the top of the stack, or %NULL
306 * if the stack is empty.
309 g_cancellable_get_current (void)
313 l = g_static_private_get (¤t_cancellable);
317 return G_CANCELLABLE (l->data);
321 * g_cancellable_reset:
322 * @cancellable: a #GCancellable object.
324 * Resets @cancellable to its uncancelled state.
327 g_cancellable_reset (GCancellable *cancellable)
329 GCancellablePrivate *priv;
331 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
335 priv = cancellable->priv;
337 while (priv->cancelled_running)
339 priv->cancelled_running_waiting = TRUE;
340 g_cond_wait (cancellable_cond,
341 g_static_mutex_get_mutex (& G_LOCK_NAME (cancellable)));
346 /* Make sure we're not leaving old cancel state around */
350 ResetEvent (priv->event);
352 if (priv->cancel_pipe[0] != -1)
358 c = read (priv->cancel_pipe[0], &ch, 1);
359 while (c == -1 && errno == EINTR);
362 priv->cancelled = FALSE;
364 G_UNLOCK(cancellable);
368 * g_cancellable_is_cancelled:
369 * @cancellable: a #GCancellable or NULL.
371 * Checks if a cancellable job has been cancelled.
373 * Returns: %TRUE if @cancellable is cancelled,
374 * FALSE if called with %NULL or if item is not cancelled.
377 g_cancellable_is_cancelled (GCancellable *cancellable)
379 return cancellable != NULL && cancellable->priv->cancelled;
383 * g_cancellable_set_error_if_cancelled:
384 * @cancellable: a #GCancellable object.
385 * @error: #GError to append error state to.
387 * If the @cancellable is cancelled, sets the error to notify
388 * that the operation was cancelled.
390 * Returns: %TRUE if @cancellable was cancelled, %FALSE if it was not.
393 g_cancellable_set_error_if_cancelled (GCancellable *cancellable,
396 if (g_cancellable_is_cancelled (cancellable))
398 g_set_error_literal (error,
400 G_IO_ERROR_CANCELLED,
401 _("Operation was cancelled"));
409 * g_cancellable_get_fd:
410 * @cancellable: a #GCancellable.
412 * Gets the file descriptor for a cancellable job. This can be used to
413 * implement cancellable operations on Unix systems. The returned fd will
414 * turn readable when @cancellable is cancelled.
416 * You are not supposed to read from the fd yourself, just check for
417 * readable status. Reading to unset the readable status is done
418 * with g_cancellable_reset().
420 * After a successful return from this function, you should use
421 * g_cancellable_release_fd() to free up resources allocated for
422 * the returned file descriptor.
424 * See also g_cancellable_make_pollfd().
426 * Returns: A valid file descriptor. %-1 if the file descriptor
427 * is not supported, or on errors.
430 g_cancellable_get_fd (GCancellable *cancellable)
432 GCancellablePrivate *priv;
435 if (cancellable == NULL)
438 priv = cancellable->priv;
444 if (priv->cancel_pipe[0] == -1)
445 g_cancellable_open_pipe (cancellable);
446 fd = priv->cancel_pipe[0];
449 G_UNLOCK(cancellable);
456 * g_cancellable_make_pollfd:
457 * @cancellable: a #GCancellable or %NULL
458 * @pollfd: a pointer to a #GPollFD
460 * Creates a #GPollFD corresponding to @cancellable; this can be passed
461 * to g_poll() and used to poll for cancellation. This is useful both
462 * for unix systems without a native poll and for portability to
465 * When this function returns %TRUE, you should use
466 * g_cancellable_release_fd() to free up resources allocated for the
467 * @pollfd. After a %FALSE return, do not call g_cancellable_release_fd().
469 * If this function returns %FALSE, either no @cancellable was given or
470 * resource limits prevent this function from allocating the necessary
471 * structures for polling. (On Linux, you will likely have reached
472 * the maximum number of file descriptors.) The suggested way to handle
473 * these cases is to ignore the @cancellable.
475 * You are not supposed to read from the fd yourself, just check for
476 * readable status. Reading to unset the readable status is done
477 * with g_cancellable_reset().
479 * Returns: %TRUE if @pollfd was successfully initialized, %FALSE on
480 * failure to prepare the cancellable.
485 g_cancellable_make_pollfd (GCancellable *cancellable, GPollFD *pollfd)
487 g_return_val_if_fail (pollfd != NULL, FALSE);
488 if (cancellable == NULL)
490 g_return_val_if_fail (G_IS_CANCELLABLE (cancellable), FALSE);
494 GCancellablePrivate *priv;
496 priv = cancellable->priv;
498 if (priv->event == NULL)
500 /* A manual reset anonymous event, starting unset */
501 priv->event = CreateEvent (NULL, TRUE, FALSE, NULL);
502 if (priv->event == NULL)
504 G_UNLOCK(cancellable);
508 SetEvent(priv->event);
511 G_UNLOCK(cancellable);
513 pollfd->fd = (gintptr)priv->event;
514 #else /* !G_OS_WIN32 */
515 int fd = g_cancellable_get_fd (cancellable);
520 #endif /* G_OS_WIN32 */
523 pollfd->events = G_IO_IN;
530 * g_cancellable_release_fd:
531 * @cancellable: a #GCancellable
533 * Releases a resources previously allocated by g_cancellable_get_fd()
534 * or g_cancellable_make_pollfd().
536 * For compatibility reasons with older releases, calling this function
537 * is not strictly required, the resources will be automatically freed
538 * when the @cancellable is finalized. However, the @cancellable will
539 * block scarce file descriptors until it is finalized if this function
540 * is not called. This can cause the application to run out of file
541 * descriptors when many #GCancellables are used at the same time.
546 g_cancellable_release_fd (GCancellable *cancellable)
548 GCancellablePrivate *priv;
550 if (cancellable == NULL)
553 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
554 g_return_if_fail (cancellable->priv->fd_refcount > 0);
556 priv = cancellable->priv;
558 G_LOCK (cancellable);
560 if (priv->fd_refcount == 0)
561 g_cancellable_close_pipe (cancellable);
562 G_UNLOCK (cancellable);
566 * g_cancellable_cancel:
567 * @cancellable: a #GCancellable object.
569 * Will set @cancellable to cancelled, and will emit the
570 * #GCancellable::cancelled signal. (However, see the warning about
571 * race conditions in the documentation for that signal if you are
572 * planning to connect to it.)
574 * This function is thread-safe. In other words, you can safely call
575 * it from a thread other than the one running the operation that was
576 * passed the @cancellable.
578 * The convention within gio is that cancelling an asynchronous
579 * operation causes it to complete asynchronously. That is, if you
580 * cancel the operation from the same thread in which it is running,
581 * then the operation's #GAsyncReadyCallback will not be invoked until
582 * the application returns to the main loop.
585 g_cancellable_cancel (GCancellable *cancellable)
587 GCancellablePrivate *priv;
589 if (cancellable == NULL ||
590 cancellable->priv->cancelled)
593 priv = cancellable->priv;
598 G_UNLOCK (cancellable);
602 priv->cancelled = TRUE;
603 priv->cancelled_running = TRUE;
606 SetEvent (priv->event);
608 if (priv->cancel_pipe[1] != -1)
614 c = write (priv->cancel_pipe[1], &ch, 1);
615 while (c == -1 && errno == EINTR);
617 G_UNLOCK(cancellable);
619 g_object_ref (cancellable);
620 g_signal_emit (cancellable, signals[CANCELLED], 0);
624 priv->cancelled_running = FALSE;
625 if (priv->cancelled_running_waiting)
626 g_cond_broadcast (cancellable_cond);
627 priv->cancelled_running_waiting = FALSE;
629 G_UNLOCK(cancellable);
631 g_object_unref (cancellable);
635 * g_cancellable_connect:
636 * @cancellable: A #GCancellable.
637 * @callback: The #GCallback to connect.
638 * @data: Data to pass to @callback.
639 * @data_destroy_func: Free function for @data or %NULL.
641 * Convenience function to connect to the #GCancellable::cancelled
642 * signal. Also handles the race condition that may happen
643 * if the cancellable is cancelled right before connecting.
645 * @callback is called at most once, either directly at the
646 * time of the connect if @cancellable is already cancelled,
647 * or when @cancellable is cancelled in some thread.
649 * @data_destroy_func will be called when the handler is
650 * disconnected, or immediately if the cancellable is already
653 * See #GCancellable::cancelled for details on how to use this.
655 * Returns: The id of the signal handler or 0 if @cancellable has already
661 g_cancellable_connect (GCancellable *cancellable,
664 GDestroyNotify data_destroy_func)
668 g_return_val_if_fail (G_IS_CANCELLABLE (cancellable), 0);
670 G_LOCK (cancellable);
672 if (cancellable->priv->cancelled)
674 void (*_callback) (GCancellable *cancellable,
677 _callback = (void *)callback;
680 _callback (cancellable, data);
682 if (data_destroy_func)
683 data_destroy_func (data);
687 id = g_signal_connect_data (cancellable, "cancelled",
689 (GClosureNotify) data_destroy_func,
692 G_UNLOCK (cancellable);
698 * g_cancellable_disconnect:
699 * @cancellable: A #GCancellable or %NULL.
700 * @handler_id: Handler id of the handler to be disconnected, or %0.
702 * Disconnects a handler from a cancellable instance similar to
703 * g_signal_handler_disconnect(). Additionally, in the event that a
704 * signal handler is currently running, this call will block until the
705 * handler has finished. Calling this function from a
706 * #GCancellable::cancelled signal handler will therefore result in a
709 * This avoids a race condition where a thread cancels at the
710 * same time as the cancellable operation is finished and the
711 * signal handler is removed. See #GCancellable::cancelled for
712 * details on how to use this.
714 * If @cancellable is %NULL or @handler_id is %0 this function does
720 g_cancellable_disconnect (GCancellable *cancellable,
723 GCancellablePrivate *priv;
725 if (handler_id == 0 || cancellable == NULL)
728 G_LOCK (cancellable);
730 priv = cancellable->priv;
732 while (priv->cancelled_running)
734 priv->cancelled_running_waiting = TRUE;
735 g_cond_wait (cancellable_cond,
736 g_static_mutex_get_mutex (& G_LOCK_NAME (cancellable)));
739 g_signal_handler_disconnect (cancellable, handler_id);
740 G_UNLOCK (cancellable);
746 GCancellable *cancellable;
748 } GCancellableSource;
751 cancellable_source_prepare (GSource *source,
754 GCancellableSource *cancellable_source = (GCancellableSource *)source;
757 return g_cancellable_is_cancelled (cancellable_source->cancellable);
761 cancellable_source_check (GSource *source)
763 GCancellableSource *cancellable_source = (GCancellableSource *)source;
765 return g_cancellable_is_cancelled (cancellable_source->cancellable);
769 cancellable_source_dispatch (GSource *source,
770 GSourceFunc callback,
773 GCancellableSourceFunc func = (GCancellableSourceFunc)callback;
774 GCancellableSource *cancellable_source = (GCancellableSource *)source;
776 return (*func) (cancellable_source->cancellable, user_data);
780 cancellable_source_finalize (GSource *source)
782 GCancellableSource *cancellable_source = (GCancellableSource *)source;
784 if (cancellable_source->cancellable)
785 g_object_unref (cancellable_source->cancellable);
789 cancellable_source_closure_callback (GCancellable *cancellable,
792 GClosure *closure = data;
794 GValue params = { 0, };
795 GValue result_value = { 0, };
798 g_value_init (&result_value, G_TYPE_BOOLEAN);
800 g_value_init (¶ms, G_TYPE_CANCELLABLE);
801 g_value_set_object (¶ms, cancellable);
803 g_closure_invoke (closure, &result_value, 1, ¶ms, NULL);
805 result = g_value_get_boolean (&result_value);
806 g_value_unset (&result_value);
807 g_value_unset (¶ms);
812 static GSourceFuncs cancellable_source_funcs =
814 cancellable_source_prepare,
815 cancellable_source_check,
816 cancellable_source_dispatch,
817 cancellable_source_finalize,
818 (GSourceFunc)cancellable_source_closure_callback,
819 (GSourceDummyMarshal)_gio_marshal_BOOLEAN__VOID,
823 * g_cancellable_source_new: (skip)
824 * @cancellable: a #GCancellable, or %NULL
826 * Creates a source that triggers if @cancellable is cancelled and
827 * calls its callback of type #GCancellableSourceFunc. This is
828 * primarily useful for attaching to another (non-cancellable) source
829 * with g_source_add_child_source() to add cancellability to it.
831 * For convenience, you can call this with a %NULL #GCancellable,
832 * in which case the source will never trigger.
834 * Return value: (transfer full): the new #GSource.
839 g_cancellable_source_new (GCancellable *cancellable)
842 GCancellableSource *cancellable_source;
844 source = g_source_new (&cancellable_source_funcs, sizeof (GCancellableSource));
845 g_source_set_name (source, "GCancellable");
846 cancellable_source = (GCancellableSource *)source;
848 if (g_cancellable_make_pollfd (cancellable,
849 &cancellable_source->pollfd))
851 cancellable_source->cancellable = g_object_ref (cancellable);
852 g_source_add_poll (source, &cancellable_source->pollfd);