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"
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,
197 set_fd_nonblocking (int fd)
201 fcntl_flags = fcntl (fd, F_GETFL);
204 fcntl_flags |= O_NONBLOCK;
206 fcntl_flags |= O_NDELAY;
209 fcntl (fd, F_SETFL, fcntl_flags);
214 set_fd_close_exec (int fd)
218 flags = fcntl (fd, F_GETFD, 0);
219 if (flags != -1 && (flags & FD_CLOEXEC) == 0)
222 fcntl (fd, F_SETFD, flags);
228 g_cancellable_open_pipe (GCancellable *cancellable)
230 GCancellablePrivate *priv;
232 priv = cancellable->priv;
233 if (pipe (priv->cancel_pipe) == 0)
235 /* Make them nonblocking, just to be sure we don't block
236 * on errors and stuff
238 set_fd_nonblocking (priv->cancel_pipe[0]);
239 set_fd_nonblocking (priv->cancel_pipe[1]);
240 set_fd_close_exec (priv->cancel_pipe[0]);
241 set_fd_close_exec (priv->cancel_pipe[1]);
249 c = write (priv->cancel_pipe[1], &ch, 1);
250 while (c == -1 && errno == EINTR);
257 g_cancellable_init (GCancellable *cancellable)
259 cancellable->priv = G_TYPE_INSTANCE_GET_PRIVATE (cancellable,
261 GCancellablePrivate);
262 cancellable->priv->cancel_pipe[0] = -1;
263 cancellable->priv->cancel_pipe[1] = -1;
269 * Creates a new #GCancellable object.
271 * Applications that want to start one or more operations
272 * that should be cancellable should create a #GCancellable
273 * and pass it to the operations.
275 * One #GCancellable can be used in multiple consecutive
276 * operations, but not in multiple concurrent operations.
278 * Returns: a #GCancellable.
281 g_cancellable_new (void)
283 return g_object_new (G_TYPE_CANCELLABLE, NULL);
287 * g_cancellable_push_current:
288 * @cancellable: a #GCancellable object
290 * Pushes @cancellable onto the cancellable stack. The current
291 * cancllable can then be recieved using g_cancellable_get_current().
293 * This is useful when implementing cancellable operations in
294 * code that does not allow you to pass down the cancellable object.
296 * This is typically called automatically by e.g. #GFile operations,
297 * so you rarely have to call this yourself.
300 g_cancellable_push_current (GCancellable *cancellable)
304 g_return_if_fail (cancellable != NULL);
306 l = g_static_private_get (¤t_cancellable);
307 l = g_slist_prepend (l, cancellable);
308 g_static_private_set (¤t_cancellable, l, NULL);
312 * g_cancellable_pop_current:
313 * @cancellable: a #GCancellable object
315 * Pops @cancellable off the cancellable stack (verifying that @cancellable
316 * is on the top of the stack).
319 g_cancellable_pop_current (GCancellable *cancellable)
323 l = g_static_private_get (¤t_cancellable);
325 g_return_if_fail (l != NULL);
326 g_return_if_fail (l->data == cancellable);
328 l = g_slist_delete_link (l, l);
329 g_static_private_set (¤t_cancellable, l, NULL);
333 * g_cancellable_get_current:
335 * Gets the top cancellable from the stack.
337 * Returns: a #GCancellable from the top of the stack, or %NULL
338 * if the stack is empty.
341 g_cancellable_get_current (void)
345 l = g_static_private_get (¤t_cancellable);
349 return G_CANCELLABLE (l->data);
353 * g_cancellable_reset:
354 * @cancellable: a #GCancellable object.
356 * Resets @cancellable to its uncancelled state.
359 g_cancellable_reset (GCancellable *cancellable)
361 GCancellablePrivate *priv;
363 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
367 priv = cancellable->priv;
369 while (priv->cancelled_running)
371 priv->cancelled_running_waiting = TRUE;
372 g_cond_wait (cancellable_cond,
373 g_static_mutex_get_mutex (& G_LOCK_NAME (cancellable)));
378 /* Make sure we're not leaving old cancel state around */
382 ResetEvent (priv->event);
384 if (priv->cancel_pipe[0] != -1)
390 c = read (priv->cancel_pipe[0], &ch, 1);
391 while (c == -1 && errno == EINTR);
394 priv->cancelled = FALSE;
396 G_UNLOCK(cancellable);
400 * g_cancellable_is_cancelled:
401 * @cancellable: a #GCancellable or NULL.
403 * Checks if a cancellable job has been cancelled.
405 * Returns: %TRUE if @cancellable is cancelled,
406 * FALSE if called with %NULL or if item is not cancelled.
409 g_cancellable_is_cancelled (GCancellable *cancellable)
411 return cancellable != NULL && cancellable->priv->cancelled;
415 * g_cancellable_set_error_if_cancelled:
416 * @cancellable: a #GCancellable object.
417 * @error: #GError to append error state to.
419 * If the @cancellable is cancelled, sets the error to notify
420 * that the operation was cancelled.
422 * Returns: %TRUE if @cancellable was cancelled, %FALSE if it was not.
425 g_cancellable_set_error_if_cancelled (GCancellable *cancellable,
428 if (g_cancellable_is_cancelled (cancellable))
430 g_set_error_literal (error,
432 G_IO_ERROR_CANCELLED,
433 _("Operation was cancelled"));
441 * g_cancellable_get_fd:
442 * @cancellable: a #GCancellable.
444 * Gets the file descriptor for a cancellable job. This can be used to
445 * implement cancellable operations on Unix systems. The returned fd will
446 * turn readable when @cancellable is cancelled.
448 * You are not supposed to read from the fd yourself, just check for
449 * readable status. Reading to unset the readable status is done
450 * with g_cancellable_reset().
452 * After a successful return from this function, you should use
453 * g_cancellable_release_fd() to free up resources allocated for
454 * the returned file descriptor.
456 * See also g_cancellable_make_pollfd().
458 * Returns: A valid file descriptor. %-1 if the file descriptor
459 * is not supported, or on errors.
462 g_cancellable_get_fd (GCancellable *cancellable)
464 GCancellablePrivate *priv;
467 if (cancellable == NULL)
470 priv = cancellable->priv;
476 if (priv->cancel_pipe[0] == -1)
477 g_cancellable_open_pipe (cancellable);
478 fd = priv->cancel_pipe[0];
481 G_UNLOCK(cancellable);
488 * g_cancellable_make_pollfd:
489 * @cancellable: a #GCancellable or %NULL
490 * @pollfd: a pointer to a #GPollFD
492 * Creates a #GPollFD corresponding to @cancellable; this can be passed
493 * to g_poll() and used to poll for cancellation. This is useful both
494 * for unix systems without a native poll and for portability to
497 * When this function returns %TRUE, you should use
498 * g_cancellable_release_fd() to free up resources allocated for the
499 * @pollfd. After a %FALSE return, do not call g_cancellable_release_fd().
501 * If this function returns %FALSE, either no @cancellable was given or
502 * resource limits prevent this function from allocating the necessary
503 * structures for polling. (On Linux, you will likely have reached
504 * the maximum number of file descriptors.) The suggested way to handle
505 * these cases is to ignore the @cancellable.
507 * You are not supposed to read from the fd yourself, just check for
508 * readable status. Reading to unset the readable status is done
509 * with g_cancellable_reset().
511 * Returns: %TRUE if @pollfd was successfully initialized, %FALSE on
512 * failure to prepare the cancellable.
517 g_cancellable_make_pollfd (GCancellable *cancellable, GPollFD *pollfd)
519 g_return_val_if_fail (pollfd != NULL, FALSE);
520 if (cancellable == NULL)
522 g_return_val_if_fail (G_IS_CANCELLABLE (cancellable), FALSE);
526 GCancellablePrivate *priv;
528 priv = cancellable->priv;
530 if (priv->event == NULL)
532 /* A manual reset anonymous event, starting unset */
533 priv->event = CreateEvent (NULL, TRUE, FALSE, NULL);
534 if (priv->event == NULL)
536 G_UNLOCK(cancellable);
540 SetEvent(priv->event);
543 G_UNLOCK(cancellable);
545 pollfd->fd = (gintptr)priv->event;
546 #else /* !G_OS_WIN32 */
547 int fd = g_cancellable_get_fd (cancellable);
552 #endif /* G_OS_WIN32 */
555 pollfd->events = G_IO_IN;
562 * g_cancellable_release_fd:
563 * @cancellable: a #GCancellable
565 * Releases a resources previously allocated by g_cancellable_get_fd()
566 * or g_cancellable_make_pollfd().
568 * For compatibility reasons with older releases, calling this function
569 * is not strictly required, the resources will be automatically freed
570 * when the @cancellable is finalized. However, the @cancellable will
571 * block scarce file descriptors until it is finalized if this function
572 * is not called. This can cause the application to run out of file
573 * descriptors when many #GCancellables are used at the same time.
578 g_cancellable_release_fd (GCancellable *cancellable)
580 GCancellablePrivate *priv;
582 if (cancellable == NULL)
585 g_return_if_fail (G_IS_CANCELLABLE (cancellable));
586 g_return_if_fail (cancellable->priv->fd_refcount > 0);
588 priv = cancellable->priv;
590 G_LOCK (cancellable);
592 if (priv->fd_refcount == 0)
593 g_cancellable_close_pipe (cancellable);
594 G_UNLOCK (cancellable);
598 * g_cancellable_cancel:
599 * @cancellable: a #GCancellable object.
601 * Will set @cancellable to cancelled, and will emit the
602 * #GCancellable::cancelled signal. (However, see the warning about
603 * race conditions in the documentation for that signal if you are
604 * planning to connect to it.)
606 * This function is thread-safe. In other words, you can safely call
607 * it from a thread other than the one running the operation that was
608 * passed the @cancellable.
610 * The convention within gio is that cancelling an asynchronous
611 * operation causes it to complete asynchronously. That is, if you
612 * cancel the operation from the same thread in which it is running,
613 * then the operation's #GAsyncReadyCallback will not be invoked until
614 * the application returns to the main loop.
617 g_cancellable_cancel (GCancellable *cancellable)
619 GCancellablePrivate *priv;
621 if (cancellable == NULL ||
622 cancellable->priv->cancelled)
625 priv = cancellable->priv;
630 G_UNLOCK (cancellable);
634 priv->cancelled = TRUE;
635 priv->cancelled_running = TRUE;
638 SetEvent (priv->event);
640 if (priv->cancel_pipe[1] != -1)
646 c = write (priv->cancel_pipe[1], &ch, 1);
647 while (c == -1 && errno == EINTR);
649 G_UNLOCK(cancellable);
651 g_object_ref (cancellable);
652 g_signal_emit (cancellable, signals[CANCELLED], 0);
656 priv->cancelled_running = FALSE;
657 if (priv->cancelled_running_waiting)
658 g_cond_broadcast (cancellable_cond);
659 priv->cancelled_running_waiting = FALSE;
661 G_UNLOCK(cancellable);
663 g_object_unref (cancellable);
667 * g_cancellable_connect:
668 * @cancellable: A #GCancellable.
669 * @callback: The #GCallback to connect.
670 * @data: Data to pass to @callback.
671 * @data_destroy_func: Free function for @data or %NULL.
673 * Convenience function to connect to the #GCancellable::cancelled
674 * signal. Also handles the race condition that may happen
675 * if the cancellable is cancelled right before connecting.
677 * @callback is called at most once, either directly at the
678 * time of the connect if @cancellable is already cancelled,
679 * or when @cancellable is cancelled in some thread.
681 * @data_destroy_func will be called when the handler is
682 * disconnected, or immediately if the cancellable is already
685 * See #GCancellable::cancelled for details on how to use this.
687 * Returns: The id of the signal handler or 0 if @cancellable has already
693 g_cancellable_connect (GCancellable *cancellable,
696 GDestroyNotify data_destroy_func)
700 g_return_val_if_fail (G_IS_CANCELLABLE (cancellable), 0);
702 G_LOCK (cancellable);
704 if (cancellable->priv->cancelled)
706 void (*_callback) (GCancellable *cancellable,
709 _callback = (void *)callback;
712 _callback (cancellable, data);
714 if (data_destroy_func)
715 data_destroy_func (data);
719 id = g_signal_connect_data (cancellable, "cancelled",
721 (GClosureNotify) data_destroy_func,
724 G_UNLOCK (cancellable);
730 * g_cancellable_disconnect:
731 * @cancellable: A #GCancellable or %NULL.
732 * @handler_id: Handler id of the handler to be disconnected, or %0.
734 * Disconnects a handler from a cancellable instance similar to
735 * g_signal_handler_disconnect(). Additionally, in the event that a
736 * signal handler is currently running, this call will block until the
737 * handler has finished. Calling this function from a
738 * #GCancellable::cancelled signal handler will therefore result in a
741 * This avoids a race condition where a thread cancels at the
742 * same time as the cancellable operation is finished and the
743 * signal handler is removed. See #GCancellable::cancelled for
744 * details on how to use this.
746 * If @cancellable is %NULL or @handler_id is %0 this function does
752 g_cancellable_disconnect (GCancellable *cancellable,
755 GCancellablePrivate *priv;
757 if (handler_id == 0 || cancellable == NULL)
760 G_LOCK (cancellable);
762 priv = cancellable->priv;
764 while (priv->cancelled_running)
766 priv->cancelled_running_waiting = TRUE;
767 g_cond_wait (cancellable_cond,
768 g_static_mutex_get_mutex (& G_LOCK_NAME (cancellable)));
771 g_signal_handler_disconnect (cancellable, handler_id);
772 G_UNLOCK (cancellable);
775 #define __G_CANCELLABLE_C__
776 #include "gioaliasdef.c"