/* GIO - GLib Input, Output and Streaming Library
*
* Copyright (C) 2006-2007 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General
* Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
*
* Author: Alexander Larsson <alexl@redhat.com>
*/
#include "config.h"
#include "glib.h"
#include <gioerror.h>
#include "glib-private.h"
#include "gcancellable.h"
#include "glibintl.h"
/**
* SECTION:gcancellable
* @short_description: Thread-safe Operation Cancellation Stack
* @include: gio/gio.h
*
* GCancellable is a thread-safe operation cancellation stack used
* throughout GIO to allow for cancellation of synchronous and
* asynchronous operations.
*/
enum {
CANCELLED,
LAST_SIGNAL
};
struct _GCancellablePrivate
{
guint cancelled : 1;
guint cancelled_running : 1;
guint cancelled_running_waiting : 1;
guint fd_refcount;
GWakeup *wakeup;
};
static guint signals[LAST_SIGNAL] = { 0 };
G_DEFINE_TYPE_WITH_PRIVATE (GCancellable, g_cancellable, G_TYPE_OBJECT)
static GPrivate current_cancellable;
static GMutex cancellable_mutex;
static GCond cancellable_cond;
static void
g_cancellable_finalize (GObject *object)
{
GCancellable *cancellable = G_CANCELLABLE (object);
if (cancellable->priv->wakeup)
GLIB_PRIVATE_CALL (g_wakeup_free) (cancellable->priv->wakeup);
G_OBJECT_CLASS (g_cancellable_parent_class)->finalize (object);
}
static void
g_cancellable_class_init (GCancellableClass *klass)
{
GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
gobject_class->finalize = g_cancellable_finalize;
/**
* GCancellable::cancelled:
* @cancellable: a #GCancellable.
*
* Emitted when the operation has been cancelled.
*
* Can be used by implementations of cancellable operations. If the
* operation is cancelled from another thread, the signal will be
* emitted in the thread that cancelled the operation, not the
* thread that is running the operation.
*
* Note that disconnecting from this signal (or any signal) in a
* multi-threaded program is prone to race conditions. For instance
* it is possible that a signal handler may be invoked even after
* a call to g_signal_handler_disconnect() for that handler has
* already returned.
*
* There is also a problem when cancellation happens right before
* connecting to the signal. If this happens the signal will
* unexpectedly not be emitted, and checking before connecting to
* the signal leaves a race condition where this is still happening.
*
* In order to make it safe and easy to connect handlers there
* are two helper functions: g_cancellable_connect() and
* g_cancellable_disconnect() which protect against problems
* like this.
*
* An example of how to us this:
* |[<!-- language="C" -->
* // Make sure we don't do unnecessary work if already cancelled
* if (g_cancellable_set_error_if_cancelled (cancellable, error))
* return;
*
* // Set up all the data needed to be able to handle cancellation
* // of the operation
* my_data = my_data_new (...);
*
* id = 0;
* if (cancellable)
* id = g_cancellable_connect (cancellable,
* G_CALLBACK (cancelled_handler)
* data, NULL);
*
* // cancellable operation here...
*
* g_cancellable_disconnect (cancellable, id);
*
* // cancelled_handler is never called after this, it is now safe
* // to free the data
* my_data_free (my_data);
* ]|
*
* Note that the cancelled signal is emitted in the thread that
* the user cancelled from, which may be the main thread. So, the
* cancellable signal should not do something that can block.
*/
signals[CANCELLED] =
g_signal_new (I_("cancelled"),
G_TYPE_FROM_CLASS (gobject_class),
G_SIGNAL_RUN_LAST,
G_STRUCT_OFFSET (GCancellableClass, cancelled),
NULL, NULL,
g_cclosure_marshal_VOID__VOID,
G_TYPE_NONE, 0);
}
static void
g_cancellable_init (GCancellable *cancellable)
{
cancellable->priv = g_cancellable_get_instance_private (cancellable);
}
/**
* g_cancellable_new:
*
* Creates a new #GCancellable object.
*
* Applications that want to start one or more operations
* that should be cancellable should create a #GCancellable
* and pass it to the operations.
*
* One #GCancellable can be used in multiple consecutive
* operations or in multiple concurrent operations.
*
* Returns: a #GCancellable.
**/
GCancellable *
g_cancellable_new (void)
{
return g_object_new (G_TYPE_CANCELLABLE, NULL);
}
/**
* g_cancellable_push_current:
* @cancellable: a #GCancellable object
*
* Pushes @cancellable onto the cancellable stack. The current
* cancellable can then be received using g_cancellable_get_current().
*
* This is useful when implementing cancellable operations in
* code that does not allow you to pass down the cancellable object.
*
* This is typically called automatically by e.g. #GFile operations,
* so you rarely have to call this yourself.
**/
void
g_cancellable_push_current (GCancellable *cancellable)
{
GSList *l;
g_return_if_fail (cancellable != NULL);
l = g_private_get (¤t_cancellable);
l = g_slist_prepend (l, cancellable);
g_private_set (¤t_cancellable, l);
}
/**
* g_cancellable_pop_current:
* @cancellable: a #GCancellable object
*
* Pops @cancellable off the cancellable stack (verifying that @cancellable
* is on the top of the stack).
**/
void
g_cancellable_pop_current (GCancellable *cancellable)
{
GSList *l;
l = g_private_get (¤t_cancellable);
g_return_if_fail (l != NULL);
g_return_if_fail (l->data == cancellable);
l = g_slist_delete_link (l, l);
g_private_set (¤t_cancellable, l);
}
/**
* g_cancellable_get_current:
*
* Gets the top cancellable from the stack.
*
* Returns: (nullable) (transfer none): a #GCancellable from the top
* of the stack, or %NULL if the stack is empty.
**/
GCancellable *
g_cancellable_get_current (void)
{
GSList *l;
l = g_private_get (¤t_cancellable);
if (l == NULL)
return NULL;
return G_CANCELLABLE (l->data);
}
/**
* g_cancellable_reset:
* @cancellable: a #GCancellable object.
*
* Resets @cancellable to its uncancelled state.
*
* If cancellable is currently in use by any cancellable operation
* then the behavior of this function is undefined.
*
* Note that it is generally not a good idea to reuse an existing
* cancellable for more operations after it has been cancelled once,
* as this function might tempt you to do. The recommended practice
* is to drop the reference to a cancellable after cancelling it,
* and let it die with the outstanding async operations. You should
* create a fresh cancellable for further async operations.
**/
void
g_cancellable_reset (GCancellable *cancellable)
{
GCancellablePrivate *priv;
g_return_if_fail (G_IS_CANCELLABLE (cancellable));
g_mutex_lock (&cancellable_mutex);
priv = cancellable->priv;
while (priv->cancelled_running)
{
priv->cancelled_running_waiting = TRUE;
g_cond_wait (&cancellable_cond, &cancellable_mutex);
}
if (priv->cancelled)
{
if (priv->wakeup)
GLIB_PRIVATE_CALL (g_wakeup_acknowledge) (priv->wakeup);
priv->cancelled = FALSE;
}
g_mutex_unlock (&cancellable_mutex);
}
/**
* g_cancellable_is_cancelled:
* @cancellable: (nullable): a #GCancellable or %NULL
*
* Checks if a cancellable job has been cancelled.
*
* Returns: %TRUE if @cancellable is cancelled,
* FALSE if called with %NULL or if item is not cancelled.
**/
gboolean
g_cancellable_is_cancelled (GCancellable *cancellable)
{
return cancellable != NULL && cancellable->priv->cancelled;
}
/**
* g_cancellable_set_error_if_cancelled:
* @cancellable: (nullable): a #GCancellable or %NULL
* @error: #GError to append error state to
*
* If the @cancellable is cancelled, sets the error to notify
* that the operation was cancelled.
*
* Returns: %TRUE if @cancellable was cancelled, %FALSE if it was not
*/
gboolean
g_cancellable_set_error_if_cancelled (GCancellable *cancellable,
GError **error)
{
if (g_cancellable_is_cancelled (cancellable))
{
g_set_error_literal (error,
G_IO_ERROR,
G_IO_ERROR_CANCELLED,
_("Operation was cancelled"));
return TRUE;
}
return FALSE;
}
/**
* g_cancellable_get_fd:
* @cancellable: a #GCancellable.
*
* Gets the file descriptor for a cancellable job. This can be used to
* implement cancellable operations on Unix systems. The returned fd will
* turn readable when @cancellable is cancelled.
*
* You are not supposed to read from the fd yourself, just check for
* readable status. Reading to unset the readable status is done
* with g_cancellable_reset().
*
* After a successful return from this function, you should use
* g_cancellable_release_fd() to free up resources allocated for
* the returned file descriptor.
*
* See also g_cancellable_make_pollfd().
*
* Returns: A valid file descriptor. %-1 if the file descriptor
* is not supported, or on errors.
**/
int
g_cancellable_get_fd (GCancellable *cancellable)
{
GPollFD pollfd;
if (cancellable == NULL)
return -1;
#ifdef G_OS_WIN32
pollfd.fd = -1;
#else
g_cancellable_make_pollfd (cancellable, &pollfd);
#endif
return pollfd.fd;
}
/**
* g_cancellable_make_pollfd:
* @cancellable: (nullable): a #GCancellable or %NULL
* @pollfd: a pointer to a #GPollFD
*
* Creates a #GPollFD corresponding to @cancellable; this can be passed
* to g_poll() and used to poll for cancellation. This is useful both
* for unix systems without a native poll and for portability to
* windows.
*
* When this function returns %TRUE, you should use
* g_cancellable_release_fd() to free up resources allocated for the
* @pollfd. After a %FALSE return, do not call g_cancellable_release_fd().
*
* If this function returns %FALSE, either no @cancellable was given or
* resource limits prevent this function from allocating the necessary
* structures for polling. (On Linux, you will likely have reached
* the maximum number of file descriptors.) The suggested way to handle
* these cases is to ignore the @cancellable.
*
* You are not supposed to read from the fd yourself, just check for
* readable status. Reading to unset the readable status is done
* with g_cancellable_reset().
*
* Returns: %TRUE if @pollfd was successfully initialized, %FALSE on
* failure to prepare the cancellable.
*
* Since: 2.22
**/
gboolean
g_cancellable_make_pollfd (GCancellable *cancellable, GPollFD *pollfd)
{
g_return_val_if_fail (pollfd != NULL, FALSE);
if (cancellable == NULL)
return FALSE;
g_return_val_if_fail (G_IS_CANCELLABLE (cancellable), FALSE);
g_mutex_lock (&cancellable_mutex);
cancellable->priv->fd_refcount++;
if (cancellable->priv->wakeup == NULL)
{
cancellable->priv->wakeup = GLIB_PRIVATE_CALL (g_wakeup_new) ();
if (cancellable->priv->cancelled)
GLIB_PRIVATE_CALL (g_wakeup_signal) (cancellable->priv->wakeup);
}
GLIB_PRIVATE_CALL (g_wakeup_get_pollfd) (cancellable->priv->wakeup, pollfd);
g_mutex_unlock (&cancellable_mutex);
return TRUE;
}
/**
* g_cancellable_release_fd:
* @cancellable: a #GCancellable
*
* Releases a resources previously allocated by g_cancellable_get_fd()
* or g_cancellable_make_pollfd().
*
* For compatibility reasons with older releases, calling this function
* is not strictly required, the resources will be automatically freed
* when the @cancellable is finalized. However, the @cancellable will
* block scarce file descriptors until it is finalized if this function
* is not called. This can cause the application to run out of file
* descriptors when many #GCancellables are used at the same time.
*
* Since: 2.22
**/
void
g_cancellable_release_fd (GCancellable *cancellable)
{
GCancellablePrivate *priv;
if (cancellable == NULL)
return;
g_return_if_fail (G_IS_CANCELLABLE (cancellable));
g_return_if_fail (cancellable->priv->fd_refcount > 0);
priv = cancellable->priv;
g_mutex_lock (&cancellable_mutex);
priv->fd_refcount--;
if (priv->fd_refcount == 0)
{
GLIB_PRIVATE_CALL (g_wakeup_free) (priv->wakeup);
priv->wakeup = NULL;
}
g_mutex_unlock (&cancellable_mutex);
}
/**
* g_cancellable_cancel:
* @cancellable: (nullable): a #GCancellable object.
*
* Will set @cancellable to cancelled, and will emit the
* #GCancellable::cancelled signal. (However, see the warning about
* race conditions in the documentation for that signal if you are
* planning to connect to it.)
*
* This function is thread-safe. In other words, you can safely call
* it from a thread other than the one running the operation that was
* passed the @cancellable.
*
* If @cancellable is %NULL, this function returns immediately for convenience.
*
* The convention within GIO is that cancelling an asynchronous
* operation causes it to complete asynchronously. That is, if you
* cancel the operation from the same thread in which it is running,
* then the operation's #GAsyncReadyCallback will not be invoked until
* the application returns to the main loop.
**/
void
g_cancellable_cancel (GCancellable *cancellable)
{
GCancellablePrivate *priv;
if (cancellable == NULL ||
cancellable->priv->cancelled)
return;
priv = cancellable->priv;
g_mutex_lock (&cancellable_mutex);
if (priv->cancelled)
{
g_mutex_unlock (&cancellable_mutex);
return;
}
priv->cancelled = TRUE;
priv->cancelled_running = TRUE;
if (priv->wakeup)
GLIB_PRIVATE_CALL (g_wakeup_signal) (priv->wakeup);
g_mutex_unlock (&cancellable_mutex);
g_object_ref (cancellable);
g_signal_emit (cancellable, signals[CANCELLED], 0);
g_mutex_lock (&cancellable_mutex);
priv->cancelled_running = FALSE;
if (priv->cancelled_running_waiting)
g_cond_broadcast (&cancellable_cond);
priv->cancelled_running_waiting = FALSE;
g_mutex_unlock (&cancellable_mutex);
g_object_unref (cancellable);
}
/**
* g_cancellable_connect:
* @cancellable: A #GCancellable.
* @callback: The #GCallback to connect.
* @data: Data to pass to @callback.
* @data_destroy_func: (nullable): Free function for @data or %NULL.
*
* Convenience function to connect to the #GCancellable::cancelled
* signal. Also handles the race condition that may happen
* if the cancellable is cancelled right before connecting.
*
* @callback is called at most once, either directly at the
* time of the connect if @cancellable is already cancelled,
* or when @cancellable is cancelled in some thread.
*
* @data_destroy_func will be called when the handler is
* disconnected, or immediately if the cancellable is already
* cancelled.
*
* See #GCancellable::cancelled for details on how to use this.
*
* Since GLib 2.40, the lock protecting @cancellable is not held when
* @callback is invoked. This lifts a restriction in place for
* earlier GLib versions which now makes it easier to write cleanup
* code that unconditionally invokes e.g. g_cancellable_cancel().
*
* Returns: The id of the signal handler or 0 if @cancellable has already
* been cancelled.
*
* Since: 2.22
*/
gulong
g_cancellable_connect (GCancellable *cancellable,
GCallback callback,
gpointer data,
GDestroyNotify data_destroy_func)
{
gulong id;
g_return_val_if_fail (G_IS_CANCELLABLE (cancellable), 0);
g_mutex_lock (&cancellable_mutex);
if (cancellable->priv->cancelled)
{
void (*_callback) (GCancellable *cancellable,
gpointer user_data);
g_mutex_unlock (&cancellable_mutex);
_callback = (void *)callback;
id = 0;
_callback (cancellable, data);
if (data_destroy_func)
data_destroy_func (data);
}
else
{
id = g_signal_connect_data (cancellable, "cancelled",
callback, data,
(GClosureNotify) data_destroy_func,
0);
g_mutex_unlock (&cancellable_mutex);
}
return id;
}
/**
* g_cancellable_disconnect:
* @cancellable: (nullable): A #GCancellable or %NULL.
* @handler_id: Handler id of the handler to be disconnected, or `0`.
*
* Disconnects a handler from a cancellable instance similar to
* g_signal_handler_disconnect(). Additionally, in the event that a
* signal handler is currently running, this call will block until the
* handler has finished. Calling this function from a
* #GCancellable::cancelled signal handler will therefore result in a
* deadlock.
*
* This avoids a race condition where a thread cancels at the
* same time as the cancellable operation is finished and the
* signal handler is removed. See #GCancellable::cancelled for
* details on how to use this.
*
* If @cancellable is %NULL or @handler_id is `0` this function does
* nothing.
*
* Since: 2.22
*/
void
g_cancellable_disconnect (GCancellable *cancellable,
gulong handler_id)
{
GCancellablePrivate *priv;
if (handler_id == 0 || cancellable == NULL)
return;
g_mutex_lock (&cancellable_mutex);
priv = cancellable->priv;
while (priv->cancelled_running)
{
priv->cancelled_running_waiting = TRUE;
g_cond_wait (&cancellable_cond, &cancellable_mutex);
}
g_signal_handler_disconnect (cancellable, handler_id);
g_mutex_unlock (&cancellable_mutex);
}
typedef struct {
GSource source;
GCancellable *cancellable;
guint cancelled_handler;
} GCancellableSource;
/*
* We can't guarantee that the source still has references, so we are
* relying on the fact that g_source_set_ready_time() no longer makes
* assertions about the reference count - the source might be in the
* window between last-unref and finalize, during which its refcount
* is officially 0. However, we *can* guarantee that it's OK to
* dereference it in a limited way, because we know we haven't yet reached
* cancellable_source_finalize() - if we had, then we would have waited
* for signal emission to finish, then disconnected the signal handler
* under the lock.
* See https://bugzilla.gnome.org/show_bug.cgi?id=791754
*/
static void
cancellable_source_cancelled (GCancellable *cancellable,
gpointer user_data)
{
GSource *source = user_data;
g_source_set_ready_time (source, 0);
}
static gboolean
cancellable_source_dispatch (GSource *source,
GSourceFunc callback,
gpointer user_data)
{
GCancellableSourceFunc func = (GCancellableSourceFunc)callback;
GCancellableSource *cancellable_source = (GCancellableSource *)source;
g_source_set_ready_time (source, -1);
return (*func) (cancellable_source->cancellable, user_data);
}
static void
cancellable_source_finalize (GSource *source)
{
GCancellableSource *cancellable_source = (GCancellableSource *)source;
if (cancellable_source->cancellable)
{
g_cancellable_disconnect (cancellable_source->cancellable,
cancellable_source->cancelled_handler);
g_object_unref (cancellable_source->cancellable);
}
}
static gboolean
cancellable_source_closure_callback (GCancellable *cancellable,
gpointer data)
{
GClosure *closure = data;
GValue params = G_VALUE_INIT;
GValue result_value = G_VALUE_INIT;
gboolean result;
g_value_init (&result_value, G_TYPE_BOOLEAN);
g_value_init (¶ms, G_TYPE_CANCELLABLE);
g_value_set_object (¶ms, cancellable);
g_closure_invoke (closure, &result_value, 1, ¶ms, NULL);
result = g_value_get_boolean (&result_value);
g_value_unset (&result_value);
g_value_unset (¶ms);
return result;
}
static GSourceFuncs cancellable_source_funcs =
{
NULL,
NULL,
cancellable_source_dispatch,
cancellable_source_finalize,
(GSourceFunc)cancellable_source_closure_callback,
};
/**
* g_cancellable_source_new: (skip)
* @cancellable: (nullable): a #GCancellable, or %NULL
*
* Creates a source that triggers if @cancellable is cancelled and
* calls its callback of type #GCancellableSourceFunc. This is
* primarily useful for attaching to another (non-cancellable) source
* with g_source_add_child_source() to add cancellability to it.
*
* For convenience, you can call this with a %NULL #GCancellable,
* in which case the source will never trigger.
*
* The new #GSource will hold a reference to the #GCancellable.
*
* Returns: (transfer full): the new #GSource.
*
* Since: 2.28
*/
GSource *
g_cancellable_source_new (GCancellable *cancellable)
{
GSource *source;
GCancellableSource *cancellable_source;
source = g_source_new (&cancellable_source_funcs, sizeof (GCancellableSource));
g_source_set_name (source, "GCancellable");
cancellable_source = (GCancellableSource *)source;
if (cancellable)
{
cancellable_source->cancellable = g_object_ref (cancellable);
/* We intentionally don't use g_cancellable_connect() here,
* because we don't want the "at most once" behavior.
*/
cancellable_source->cancelled_handler =
g_signal_connect (cancellable, "cancelled",
G_CALLBACK (cancellable_source_cancelled),
source);
if (g_cancellable_is_cancelled (cancellable))
g_source_set_ready_time (source, 0);
}
return source;
}