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.
248 * Note that it is generally not a good idea to reuse an existing
249 * cancellable for more operations after it has been cancelled once,
250 * as this function might tempt you to do. The recommended practice
251 * is to drop the reference to a cancellable after cancelling it,
252 * and let it die with the outstanding async operations. You should
253 * create a fresh cancellable for further async operations.
256 g_cancellable_reset (GCancellable
*cancellable
)
258 GCancellablePrivate
*priv
;
260 g_return_if_fail (G_IS_CANCELLABLE (cancellable
));
262 g_mutex_lock (&cancellable_mutex
);
264 priv
= cancellable
->priv
;
266 while (priv
->cancelled_running
)
268 priv
->cancelled_running_waiting
= TRUE
;
269 g_cond_wait (&cancellable_cond
, &cancellable_mutex
);
275 GLIB_PRIVATE_CALL (g_wakeup_acknowledge
) (priv
->wakeup
);
277 priv
->cancelled
= FALSE
;
280 g_mutex_unlock (&cancellable_mutex
);
284 * g_cancellable_is_cancelled:
285 * @cancellable: (nullable): a #GCancellable or %NULL
287 * Checks if a cancellable job has been cancelled.
289 * Returns: %TRUE if @cancellable is cancelled,
290 * FALSE if called with %NULL or if item is not cancelled.
293 g_cancellable_is_cancelled (GCancellable
*cancellable
)
295 return cancellable
!= NULL
&& cancellable
->priv
->cancelled
;
299 * g_cancellable_set_error_if_cancelled:
300 * @cancellable: (nullable): a #GCancellable or %NULL
301 * @error: #GError to append error state to
303 * If the @cancellable is cancelled, sets the error to notify
304 * that the operation was cancelled.
306 * Returns: %TRUE if @cancellable was cancelled, %FALSE if it was not
309 g_cancellable_set_error_if_cancelled (GCancellable
*cancellable
,
312 if (g_cancellable_is_cancelled (cancellable
))
314 g_set_error_literal (error
,
316 G_IO_ERROR_CANCELLED
,
317 _("Operation was cancelled"));
325 * g_cancellable_get_fd:
326 * @cancellable: a #GCancellable.
328 * Gets the file descriptor for a cancellable job. This can be used to
329 * implement cancellable operations on Unix systems. The returned fd will
330 * turn readable when @cancellable is cancelled.
332 * You are not supposed to read from the fd yourself, just check for
333 * readable status. Reading to unset the readable status is done
334 * with g_cancellable_reset().
336 * After a successful return from this function, you should use
337 * g_cancellable_release_fd() to free up resources allocated for
338 * the returned file descriptor.
340 * See also g_cancellable_make_pollfd().
342 * Returns: A valid file descriptor. %-1 if the file descriptor
343 * is not supported, or on errors.
346 g_cancellable_get_fd (GCancellable
*cancellable
)
350 if (cancellable
== NULL
)
356 g_cancellable_make_pollfd (cancellable
, &pollfd
);
363 * g_cancellable_make_pollfd:
364 * @cancellable: (nullable): a #GCancellable or %NULL
365 * @pollfd: a pointer to a #GPollFD
367 * Creates a #GPollFD corresponding to @cancellable; this can be passed
368 * to g_poll() and used to poll for cancellation. This is useful both
369 * for unix systems without a native poll and for portability to
372 * When this function returns %TRUE, you should use
373 * g_cancellable_release_fd() to free up resources allocated for the
374 * @pollfd. After a %FALSE return, do not call g_cancellable_release_fd().
376 * If this function returns %FALSE, either no @cancellable was given or
377 * resource limits prevent this function from allocating the necessary
378 * structures for polling. (On Linux, you will likely have reached
379 * the maximum number of file descriptors.) The suggested way to handle
380 * these cases is to ignore the @cancellable.
382 * You are not supposed to read from the fd yourself, just check for
383 * readable status. Reading to unset the readable status is done
384 * with g_cancellable_reset().
386 * Returns: %TRUE if @pollfd was successfully initialized, %FALSE on
387 * failure to prepare the cancellable.
392 g_cancellable_make_pollfd (GCancellable
*cancellable
, GPollFD
*pollfd
)
394 g_return_val_if_fail (pollfd
!= NULL
, FALSE
);
395 if (cancellable
== NULL
)
397 g_return_val_if_fail (G_IS_CANCELLABLE (cancellable
), FALSE
);
399 g_mutex_lock (&cancellable_mutex
);
401 cancellable
->priv
->fd_refcount
++;
403 if (cancellable
->priv
->wakeup
== NULL
)
405 cancellable
->priv
->wakeup
= GLIB_PRIVATE_CALL (g_wakeup_new
) ();
407 if (cancellable
->priv
->cancelled
)
408 GLIB_PRIVATE_CALL (g_wakeup_signal
) (cancellable
->priv
->wakeup
);
411 GLIB_PRIVATE_CALL (g_wakeup_get_pollfd
) (cancellable
->priv
->wakeup
, pollfd
);
413 g_mutex_unlock (&cancellable_mutex
);
419 * g_cancellable_release_fd:
420 * @cancellable: a #GCancellable
422 * Releases a resources previously allocated by g_cancellable_get_fd()
423 * or g_cancellable_make_pollfd().
425 * For compatibility reasons with older releases, calling this function
426 * is not strictly required, the resources will be automatically freed
427 * when the @cancellable is finalized. However, the @cancellable will
428 * block scarce file descriptors until it is finalized if this function
429 * is not called. This can cause the application to run out of file
430 * descriptors when many #GCancellables are used at the same time.
435 g_cancellable_release_fd (GCancellable
*cancellable
)
437 GCancellablePrivate
*priv
;
439 if (cancellable
== NULL
)
442 g_return_if_fail (G_IS_CANCELLABLE (cancellable
));
443 g_return_if_fail (cancellable
->priv
->fd_refcount
> 0);
445 priv
= cancellable
->priv
;
447 g_mutex_lock (&cancellable_mutex
);
450 if (priv
->fd_refcount
== 0)
452 GLIB_PRIVATE_CALL (g_wakeup_free
) (priv
->wakeup
);
456 g_mutex_unlock (&cancellable_mutex
);
460 * g_cancellable_cancel:
461 * @cancellable: (nullable): a #GCancellable object.
463 * Will set @cancellable to cancelled, and will emit the
464 * #GCancellable::cancelled signal. (However, see the warning about
465 * race conditions in the documentation for that signal if you are
466 * planning to connect to it.)
468 * This function is thread-safe. In other words, you can safely call
469 * it from a thread other than the one running the operation that was
470 * passed the @cancellable.
472 * If @cancellable is %NULL, this function returns immediately for convenience.
474 * The convention within GIO is that cancelling an asynchronous
475 * operation causes it to complete asynchronously. That is, if you
476 * cancel the operation from the same thread in which it is running,
477 * then the operation's #GAsyncReadyCallback will not be invoked until
478 * the application returns to the main loop.
481 g_cancellable_cancel (GCancellable
*cancellable
)
483 GCancellablePrivate
*priv
;
485 if (cancellable
== NULL
||
486 cancellable
->priv
->cancelled
)
489 priv
= cancellable
->priv
;
491 g_mutex_lock (&cancellable_mutex
);
495 g_mutex_unlock (&cancellable_mutex
);
499 priv
->cancelled
= TRUE
;
500 priv
->cancelled_running
= TRUE
;
503 GLIB_PRIVATE_CALL (g_wakeup_signal
) (priv
->wakeup
);
505 g_mutex_unlock (&cancellable_mutex
);
507 g_object_ref (cancellable
);
508 g_signal_emit (cancellable
, signals
[CANCELLED
], 0);
510 g_mutex_lock (&cancellable_mutex
);
512 priv
->cancelled_running
= FALSE
;
513 if (priv
->cancelled_running_waiting
)
514 g_cond_broadcast (&cancellable_cond
);
515 priv
->cancelled_running_waiting
= FALSE
;
517 g_mutex_unlock (&cancellable_mutex
);
519 g_object_unref (cancellable
);
523 * g_cancellable_connect:
524 * @cancellable: A #GCancellable.
525 * @callback: The #GCallback to connect.
526 * @data: Data to pass to @callback.
527 * @data_destroy_func: (nullable): Free function for @data or %NULL.
529 * Convenience function to connect to the #GCancellable::cancelled
530 * signal. Also handles the race condition that may happen
531 * if the cancellable is cancelled right before connecting.
533 * @callback is called at most once, either directly at the
534 * time of the connect if @cancellable is already cancelled,
535 * or when @cancellable is cancelled in some thread.
537 * @data_destroy_func will be called when the handler is
538 * disconnected, or immediately if the cancellable is already
541 * See #GCancellable::cancelled for details on how to use this.
543 * Since GLib 2.40, the lock protecting @cancellable is not held when
544 * @callback is invoked. This lifts a restriction in place for
545 * earlier GLib versions which now makes it easier to write cleanup
546 * code that unconditionally invokes e.g. g_cancellable_cancel().
548 * Returns: The id of the signal handler or 0 if @cancellable has already
554 g_cancellable_connect (GCancellable
*cancellable
,
557 GDestroyNotify data_destroy_func
)
561 g_return_val_if_fail (G_IS_CANCELLABLE (cancellable
), 0);
563 g_mutex_lock (&cancellable_mutex
);
565 if (cancellable
->priv
->cancelled
)
567 void (*_callback
) (GCancellable
*cancellable
,
570 g_mutex_unlock (&cancellable_mutex
);
572 _callback
= (void *)callback
;
575 _callback (cancellable
, data
);
577 if (data_destroy_func
)
578 data_destroy_func (data
);
582 id
= g_signal_connect_data (cancellable
, "cancelled",
584 (GClosureNotify
) data_destroy_func
,
587 g_mutex_unlock (&cancellable_mutex
);
595 * g_cancellable_disconnect:
596 * @cancellable: (nullable): A #GCancellable or %NULL.
597 * @handler_id: Handler id of the handler to be disconnected, or %0.
599 * Disconnects a handler from a cancellable instance similar to
600 * g_signal_handler_disconnect(). Additionally, in the event that a
601 * signal handler is currently running, this call will block until the
602 * handler has finished. Calling this function from a
603 * #GCancellable::cancelled signal handler will therefore result in a
606 * This avoids a race condition where a thread cancels at the
607 * same time as the cancellable operation is finished and the
608 * signal handler is removed. See #GCancellable::cancelled for
609 * details on how to use this.
611 * If @cancellable is %NULL or @handler_id is %0 this function does
617 g_cancellable_disconnect (GCancellable
*cancellable
,
620 GCancellablePrivate
*priv
;
622 if (handler_id
== 0 || cancellable
== NULL
)
625 g_mutex_lock (&cancellable_mutex
);
627 priv
= cancellable
->priv
;
629 while (priv
->cancelled_running
)
631 priv
->cancelled_running_waiting
= TRUE
;
632 g_cond_wait (&cancellable_cond
, &cancellable_mutex
);
635 g_signal_handler_disconnect (cancellable
, handler_id
);
637 g_mutex_unlock (&cancellable_mutex
);
643 GCancellable
*cancellable
;
644 guint cancelled_handler
;
645 } GCancellableSource
;
648 cancellable_source_cancelled (GCancellable
*cancellable
,
651 GSource
*source
= user_data
;
653 g_source_set_ready_time (source
, 0);
657 cancellable_source_dispatch (GSource
*source
,
658 GSourceFunc callback
,
661 GCancellableSourceFunc func
= (GCancellableSourceFunc
)callback
;
662 GCancellableSource
*cancellable_source
= (GCancellableSource
*)source
;
664 g_source_set_ready_time (source
, -1);
665 return (*func
) (cancellable_source
->cancellable
, user_data
);
669 cancellable_source_finalize (GSource
*source
)
671 GCancellableSource
*cancellable_source
= (GCancellableSource
*)source
;
673 if (cancellable_source
->cancellable
)
675 g_cancellable_disconnect (cancellable_source
->cancellable
,
676 cancellable_source
->cancelled_handler
);
677 g_object_unref (cancellable_source
->cancellable
);
682 cancellable_source_closure_callback (GCancellable
*cancellable
,
685 GClosure
*closure
= data
;
687 GValue params
= G_VALUE_INIT
;
688 GValue result_value
= G_VALUE_INIT
;
691 g_value_init (&result_value
, G_TYPE_BOOLEAN
);
693 g_value_init (¶ms
, G_TYPE_CANCELLABLE
);
694 g_value_set_object (¶ms
, cancellable
);
696 g_closure_invoke (closure
, &result_value
, 1, ¶ms
, NULL
);
698 result
= g_value_get_boolean (&result_value
);
699 g_value_unset (&result_value
);
700 g_value_unset (¶ms
);
705 static GSourceFuncs cancellable_source_funcs
=
709 cancellable_source_dispatch
,
710 cancellable_source_finalize
,
711 (GSourceFunc
)cancellable_source_closure_callback
,
715 * g_cancellable_source_new: (skip)
716 * @cancellable: (nullable): a #GCancellable, or %NULL
718 * Creates a source that triggers if @cancellable is cancelled and
719 * calls its callback of type #GCancellableSourceFunc. This is
720 * primarily useful for attaching to another (non-cancellable) source
721 * with g_source_add_child_source() to add cancellability to it.
723 * For convenience, you can call this with a %NULL #GCancellable,
724 * in which case the source will never trigger.
726 * The new #GSource will hold a reference to the #GCancellable.
728 * Returns: (transfer full): the new #GSource.
733 g_cancellable_source_new (GCancellable
*cancellable
)
736 GCancellableSource
*cancellable_source
;
738 source
= g_source_new (&cancellable_source_funcs
, sizeof (GCancellableSource
));
739 g_source_set_name (source
, "GCancellable");
740 cancellable_source
= (GCancellableSource
*)source
;
744 cancellable_source
->cancellable
= g_object_ref (cancellable
);
746 /* We intentionally don't use g_cancellable_connect() here,
747 * because we don't want the "at most once" behavior.
749 cancellable_source
->cancelled_handler
=
750 g_signal_connect (cancellable
, "cancelled",
751 G_CALLBACK (cancellable_source_cancelled
),
753 if (g_cancellable_is_cancelled (cancellable
))
754 g_source_set_ready_time (source
, 0);