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>
34 #include "gcancellable.h"
39 * SECTION:gcancellable
40 * @short_description: Thread-safe Operation Cancellation Stack
43 * GCancellable is a thread-safe operation cancellation stack used
44 * throughout GIO to allow for cancellation of synchronous and
45 * asynchronous operations.
53 struct _GCancellablePrivate
56 guint cancelled_running : 1;
57 guint cancelled_running_waiting : 1;
67 static guint signals[LAST_SIGNAL] = { 0 };
69 G_DEFINE_TYPE (GCancellable, g_cancellable, G_TYPE_OBJECT);
71 static GStaticPrivate current_cancellable = G_STATIC_PRIVATE_INIT;
72 G_LOCK_DEFINE_STATIC(cancellable);
73 static GCond *cancellable_cond = NULL;
76 g_cancellable_close_pipe (GCancellable *cancellable)
78 GCancellablePrivate *priv;
80 priv = cancellable->priv;
82 if (priv->cancel_pipe[0] != -1)
84 close (priv->cancel_pipe[0]);
85 priv->cancel_pipe[0] = -1;
88 if (priv->cancel_pipe[1] != -1)
90 close (priv->cancel_pipe[1]);
91 priv->cancel_pipe[1] = -1;
97 CloseHandle (priv->event);
104 g_cancellable_finalize (GObject *object)
106 GCancellable *cancellable = G_CANCELLABLE (object);
108 g_cancellable_close_pipe (cancellable);
110 G_OBJECT_CLASS (g_cancellable_parent_class)->finalize (object);
114 g_cancellable_class_init (GCancellableClass *klass)
116 GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
118 g_type_class_add_private (klass, sizeof (GCancellablePrivate));
120 if (cancellable_cond == NULL && g_thread_supported ())
121 cancellable_cond = g_cond_new ();
123 gobject_class->finalize = g_cancellable_finalize;
126 * GCancellable::cancelled:
127 * @cancellable: a #GCancellable.
129 * Emitted when the operation has been cancelled.
131 * Can be used by implementations of cancellable operations. If the
132 * operation is cancelled from another thread, the signal will be
133 * emitted in the thread that cancelled the operation, not the
134 * thread that is running the operation.
136 * Note that disconnecting from this signal (or any signal) in a
137 * multi-threaded program is prone to race conditions. For instance
138 * it is possible that a signal handler may be invoked even
139 * <emphasis>after</emphasis> a call to
140 * g_signal_handler_disconnect() for that handler has already
143 * There is also a problem when cancellation happen
144 * right before connecting to the signal. If this happens the
145 * signal will unexpectedly not be emitted, and checking before
146 * connecting to the signal leaves a race condition where this is
149 * In order to make it safe and easy to connect handlers there
150 * are two helper functions: g_cancellable_connect() and
151 * g_cancellable_disconnect() which protect against problems
154 * An example of how to us this:
156 * /<!-- -->* Make sure we don't do any unnecessary work if already cancelled *<!-- -->/
157 * if (g_cancellable_set_error_if_cancelled (cancellable))
160 * /<!-- -->* Set up all the data needed to be able to
161 * * handle cancellation of the operation *<!-- -->/
162 * my_data = my_data_new (...);
166 * id = g_cancellable_connect (cancellable,
167 * G_CALLBACK (cancelled_handler)
170 * /<!-- -->* cancellable operation here... *<!-- -->/
172 * g_cancellable_disconnect (cancellable, id);
174 * /<!-- -->* cancelled_handler is never called after this, it
175 * * is now safe to free the data *<!-- -->/
176 * my_data_free (my_data);
179 * Note that the cancelled signal is emitted in the thread that
180 * the user cancelled from, which may be the main thread. So, the
181 * cancellable signal should not do something that can block.
184 g_signal_new (I_("cancelled"),
185 G_TYPE_FROM_CLASS (gobject_class),
187 G_STRUCT_OFFSET (GCancellableClass, cancelled),
189 g_cclosure_marshal_VOID__VOID,
196 set_fd_nonblocking (int fd)
200 fcntl_flags = fcntl (fd, F_GETFL);
203 fcntl_flags |= O_NONBLOCK;
205 fcntl_flags |= O_NDELAY;
208 fcntl (fd, F_SETFL, fcntl_flags);
213 set_fd_close_exec (int fd)
217 flags = fcntl (fd, F_GETFD, 0);
218 if (flags != -1 && (flags & FD_CLOEXEC) == 0)
221 fcntl (fd, F_SETFD, flags);
227 g_cancellable_open_pipe (GCancellable *cancellable)
229 GCancellablePrivate *priv;
231 priv = cancellable->priv;
232 if (pipe (priv->cancel_pipe) == 0)
234 /* Make them nonblocking, just to be sure we don't block
235 * on errors and stuff
237 set_fd_nonblocking (priv->cancel_pipe[0]);
238 set_fd_nonblocking (priv->cancel_pipe[1]);
239 set_fd_close_exec (priv->cancel_pipe[0]);
240 set_fd_close_exec (priv->cancel_pipe[1]);
248 c = write (priv->cancel_pipe[1], &ch, 1);
249 while (c == -1 && errno == EINTR);
256 g_cancellable_init (GCancellable *cancellable)
258 cancellable->priv = G_TYPE_INSTANCE_GET_PRIVATE (cancellable,
260 GCancellablePrivate);
261 cancellable->priv->cancel_pipe[0] = -1;
262 cancellable->priv->cancel_pipe[1] = -1;
268 * Creates a new #GCancellable object.
270 * Applications that want to start one or more operations
271 * that should be cancellable should create a #GCancellable
272 * and pass it to the operations.
274 * One #GCancellable can be used in multiple consecutive
275 * operations, but not in multiple concurrent operations.
277 * Returns: a #GCancellable.
280 g_cancellable_new (void)
282 return g_object_new (G_TYPE_CANCELLABLE, NULL);
286 * g_cancellable_push_current:
287 * @cancellable: a #GCancellable object
289 * Pushes @cancellable onto the cancellable stack. The current
290 * cancllable can then be recieved using g_cancellable_get_current().
292 * This is useful when implementing cancellable operations in
293 * code that does not allow you to pass down the cancellable object.
295 * This is typically called automatically by e.g. #GFile operations,
296 * so you rarely have to call this yourself.
299 g_cancellable_push_current (GCancellable *cancellable)
303 g_return_if_fail (cancellable != NULL);
305 l = g_static_private_get (¤t_cancellable);
306 l = g_slist_prepend (l, cancellable);
307 g_static_private_set (¤t_cancellable, l, NULL);
311 * g_cancellable_pop_current:
312 * @cancellable: a #GCancellable object
314 * Pops @cancellable off the cancellable stack (verifying that @cancellable
315 * is on the top of the stack).
318 g_cancellable_pop_current (GCancellable *cancellable)
322 l = g_static_private_get (¤t_cancellable);
324 g_return_if_fail (l != NULL);
325 g_return_if_fail (l->data == cancellable);
327 l = g_slist_delete_link (l, l);
328 g_static_private_set (¤t_cancellable, l, NULL);
332 * g_cancellable_get_current:
334 * Gets the top cancellable from the stack.
336 * Returns: (transfer none): a #GCancellable from the top of the stack, or %NULL
337 * if the stack is empty.
340 g_cancellable_get_current (void)
344 l = g_static_private_get (¤t_cancellable);
348 return G_CANCELLABLE (l->data);
352 * g_cancellable_reset:
353 * @cancellable: a #GCancellable object.
355 * Resets @cancellable to its uncancelled state.
358 g_cancellable_reset (GCancellable *cancellable)
360 GCancellablePrivate *priv;
362 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
366 priv = cancellable->priv;
368 while (priv->cancelled_running)
370 priv->cancelled_running_waiting = TRUE;
371 g_cond_wait (cancellable_cond,
372 g_static_mutex_get_mutex (& G_LOCK_NAME (cancellable)));
377 /* Make sure we're not leaving old cancel state around */
381 ResetEvent (priv->event);
383 if (priv->cancel_pipe[0] != -1)
389 c = read (priv->cancel_pipe[0], &ch, 1);
390 while (c == -1 && errno == EINTR);
393 priv->cancelled = FALSE;
395 G_UNLOCK(cancellable);
399 * g_cancellable_is_cancelled:
400 * @cancellable: a #GCancellable or NULL.
402 * Checks if a cancellable job has been cancelled.
404 * Returns: %TRUE if @cancellable is cancelled,
405 * FALSE if called with %NULL or if item is not cancelled.
408 g_cancellable_is_cancelled (GCancellable *cancellable)
410 return cancellable != NULL && cancellable->priv->cancelled;
414 * g_cancellable_set_error_if_cancelled:
415 * @cancellable: a #GCancellable object.
416 * @error: #GError to append error state to.
418 * If the @cancellable is cancelled, sets the error to notify
419 * that the operation was cancelled.
421 * Returns: %TRUE if @cancellable was cancelled, %FALSE if it was not.
424 g_cancellable_set_error_if_cancelled (GCancellable *cancellable,
427 if (g_cancellable_is_cancelled (cancellable))
429 g_set_error_literal (error,
431 G_IO_ERROR_CANCELLED,
432 _("Operation was cancelled"));
440 * g_cancellable_get_fd:
441 * @cancellable: a #GCancellable.
443 * Gets the file descriptor for a cancellable job. This can be used to
444 * implement cancellable operations on Unix systems. The returned fd will
445 * turn readable when @cancellable is cancelled.
447 * You are not supposed to read from the fd yourself, just check for
448 * readable status. Reading to unset the readable status is done
449 * with g_cancellable_reset().
451 * After a successful return from this function, you should use
452 * g_cancellable_release_fd() to free up resources allocated for
453 * the returned file descriptor.
455 * See also g_cancellable_make_pollfd().
457 * Returns: A valid file descriptor. %-1 if the file descriptor
458 * is not supported, or on errors.
461 g_cancellable_get_fd (GCancellable *cancellable)
463 GCancellablePrivate *priv;
466 if (cancellable == NULL)
469 priv = cancellable->priv;
475 if (priv->cancel_pipe[0] == -1)
476 g_cancellable_open_pipe (cancellable);
477 fd = priv->cancel_pipe[0];
480 G_UNLOCK(cancellable);
487 * g_cancellable_make_pollfd:
488 * @cancellable: a #GCancellable or %NULL
489 * @pollfd: a pointer to a #GPollFD
491 * Creates a #GPollFD corresponding to @cancellable; this can be passed
492 * to g_poll() and used to poll for cancellation. This is useful both
493 * for unix systems without a native poll and for portability to
496 * When this function returns %TRUE, you should use
497 * g_cancellable_release_fd() to free up resources allocated for the
498 * @pollfd. After a %FALSE return, do not call g_cancellable_release_fd().
500 * If this function returns %FALSE, either no @cancellable was given or
501 * resource limits prevent this function from allocating the necessary
502 * structures for polling. (On Linux, you will likely have reached
503 * the maximum number of file descriptors.) The suggested way to handle
504 * these cases is to ignore the @cancellable.
506 * You are not supposed to read from the fd yourself, just check for
507 * readable status. Reading to unset the readable status is done
508 * with g_cancellable_reset().
510 * Returns: %TRUE if @pollfd was successfully initialized, %FALSE on
511 * failure to prepare the cancellable.
516 g_cancellable_make_pollfd (GCancellable *cancellable, GPollFD *pollfd)
518 g_return_val_if_fail (pollfd != NULL, FALSE);
519 if (cancellable == NULL)
521 g_return_val_if_fail (G_IS_CANCELLABLE (cancellable), FALSE);
525 GCancellablePrivate *priv;
527 priv = cancellable->priv;
529 if (priv->event == NULL)
531 /* A manual reset anonymous event, starting unset */
532 priv->event = CreateEvent (NULL, TRUE, FALSE, NULL);
533 if (priv->event == NULL)
535 G_UNLOCK(cancellable);
539 SetEvent(priv->event);
542 G_UNLOCK(cancellable);
544 pollfd->fd = (gintptr)priv->event;
545 #else /* !G_OS_WIN32 */
546 int fd = g_cancellable_get_fd (cancellable);
551 #endif /* G_OS_WIN32 */
554 pollfd->events = G_IO_IN;
561 * g_cancellable_release_fd:
562 * @cancellable: a #GCancellable
564 * Releases a resources previously allocated by g_cancellable_get_fd()
565 * or g_cancellable_make_pollfd().
567 * For compatibility reasons with older releases, calling this function
568 * is not strictly required, the resources will be automatically freed
569 * when the @cancellable is finalized. However, the @cancellable will
570 * block scarce file descriptors until it is finalized if this function
571 * is not called. This can cause the application to run out of file
572 * descriptors when many #GCancellables are used at the same time.
577 g_cancellable_release_fd (GCancellable *cancellable)
579 GCancellablePrivate *priv;
581 if (cancellable == NULL)
584 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
585 g_return_if_fail (cancellable->priv->fd_refcount > 0);
587 priv = cancellable->priv;
589 G_LOCK (cancellable);
591 if (priv->fd_refcount == 0)
592 g_cancellable_close_pipe (cancellable);
593 G_UNLOCK (cancellable);
597 * g_cancellable_cancel:
598 * @cancellable: a #GCancellable object.
600 * Will set @cancellable to cancelled, and will emit the
601 * #GCancellable::cancelled signal. (However, see the warning about
602 * race conditions in the documentation for that signal if you are
603 * planning to connect to it.)
605 * This function is thread-safe. In other words, you can safely call
606 * it from a thread other than the one running the operation that was
607 * passed the @cancellable.
609 * The convention within gio is that cancelling an asynchronous
610 * operation causes it to complete asynchronously. That is, if you
611 * cancel the operation from the same thread in which it is running,
612 * then the operation's #GAsyncReadyCallback will not be invoked until
613 * the application returns to the main loop.
616 g_cancellable_cancel (GCancellable *cancellable)
618 GCancellablePrivate *priv;
620 if (cancellable == NULL ||
621 cancellable->priv->cancelled)
624 priv = cancellable->priv;
629 G_UNLOCK (cancellable);
633 priv->cancelled = TRUE;
634 priv->cancelled_running = TRUE;
637 SetEvent (priv->event);
639 if (priv->cancel_pipe[1] != -1)
645 c = write (priv->cancel_pipe[1], &ch, 1);
646 while (c == -1 && errno == EINTR);
648 G_UNLOCK(cancellable);
650 g_object_ref (cancellable);
651 g_signal_emit (cancellable, signals[CANCELLED], 0);
655 priv->cancelled_running = FALSE;
656 if (priv->cancelled_running_waiting)
657 g_cond_broadcast (cancellable_cond);
658 priv->cancelled_running_waiting = FALSE;
660 G_UNLOCK(cancellable);
662 g_object_unref (cancellable);
666 * g_cancellable_connect:
667 * @cancellable: A #GCancellable.
668 * @callback: The #GCallback to connect.
669 * @data: Data to pass to @callback.
670 * @data_destroy_func: Free function for @data or %NULL.
672 * Convenience function to connect to the #GCancellable::cancelled
673 * signal. Also handles the race condition that may happen
674 * if the cancellable is cancelled right before connecting.
676 * @callback is called at most once, either directly at the
677 * time of the connect if @cancellable is already cancelled,
678 * or when @cancellable is cancelled in some thread.
680 * @data_destroy_func will be called when the handler is
681 * disconnected, or immediately if the cancellable is already
684 * See #GCancellable::cancelled for details on how to use this.
686 * Returns: The id of the signal handler or 0 if @cancellable has already
692 g_cancellable_connect (GCancellable *cancellable,
695 GDestroyNotify data_destroy_func)
699 g_return_val_if_fail (G_IS_CANCELLABLE (cancellable), 0);
701 G_LOCK (cancellable);
703 if (cancellable->priv->cancelled)
705 void (*_callback) (GCancellable *cancellable,
708 _callback = (void *)callback;
711 _callback (cancellable, data);
713 if (data_destroy_func)
714 data_destroy_func (data);
718 id = g_signal_connect_data (cancellable, "cancelled",
720 (GClosureNotify) data_destroy_func,
723 G_UNLOCK (cancellable);
729 * g_cancellable_disconnect:
730 * @cancellable: A #GCancellable or %NULL.
731 * @handler_id: Handler id of the handler to be disconnected, or %0.
733 * Disconnects a handler from a cancellable instance similar to
734 * g_signal_handler_disconnect(). Additionally, in the event that a
735 * signal handler is currently running, this call will block until the
736 * handler has finished. Calling this function from a
737 * #GCancellable::cancelled signal handler will therefore result in a
740 * This avoids a race condition where a thread cancels at the
741 * same time as the cancellable operation is finished and the
742 * signal handler is removed. See #GCancellable::cancelled for
743 * details on how to use this.
745 * If @cancellable is %NULL or @handler_id is %0 this function does
751 g_cancellable_disconnect (GCancellable *cancellable,
754 GCancellablePrivate *priv;
756 if (handler_id == 0 || cancellable == NULL)
759 G_LOCK (cancellable);
761 priv = cancellable->priv;
763 while (priv->cancelled_running)
765 priv->cancelled_running_waiting = TRUE;
766 g_cond_wait (cancellable_cond,
767 g_static_mutex_get_mutex (& G_LOCK_NAME (cancellable)));
770 g_signal_handler_disconnect (cancellable, handler_id);
771 G_UNLOCK (cancellable);