glib/gio/gcancellable.c

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/* 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 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, write to the
* Free Software Foundation, Inc., 59 Temple Place, Suite 330,
* Boston, MA 02111-1307, USA.
*
* Author: Alexander Larsson <alexl@redhat.com>
*/
#include "config.h"
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#include <errno.h>
#include <fcntl.h>
#include <gioerror.h>
#ifdef G_OS_WIN32
#include <windows.h>
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#include <io.h>
#endif
#include "gcancellable.h"
#include "glibintl.h"
#include "gioalias.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;
int cancel_pipe[2];
#ifdef G_OS_WIN32
HANDLE event;
#endif
};
static guint signals[LAST_SIGNAL] = { 0 };
G_DEFINE_TYPE (GCancellable, g_cancellable, G_TYPE_OBJECT);
static GStaticPrivate current_cancellable = G_STATIC_PRIVATE_INIT;
G_LOCK_DEFINE_STATIC(cancellable);
static GCond *cancellable_cond = NULL;
static void
g_cancellable_close_pipe (GCancellable *cancellable)
{
GCancellablePrivate *priv;
priv = cancellable->priv;
if (priv->cancel_pipe[0] != -1)
{
close (priv->cancel_pipe[0]);
priv->cancel_pipe[0] = -1;
}
if (priv->cancel_pipe[1] != -1)
{
close (priv->cancel_pipe[1]);
priv->cancel_pipe[1] = -1;
}
#ifdef G_OS_WIN32
if (priv->event)
{
CloseHandle (priv->event);
priv->event = NULL;
}
#endif
}
static void
g_cancellable_finalize (GObject *object)
{
GCancellable *cancellable = G_CANCELLABLE (object);
g_cancellable_close_pipe (cancellable);
G_OBJECT_CLASS (g_cancellable_parent_class)->finalize (object);
}
static void
g_cancellable_class_init (GCancellableClass *klass)
{
GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
g_type_class_add_private (klass, sizeof (GCancellablePrivate));
if (cancellable_cond == NULL && g_thread_supported ())
cancellable_cond = g_cond_new ();
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
* <emphasis>after</emphasis> a call to
* g_signal_handler_disconnect() for that handler has already
* returned.
*
* There is also a problem when cancellation happen
* 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:
* |[
* /<!-- -->* Make sure we don't do any unnecessary work if already cancelled *<!-- -->/
* if (g_cancellable_set_error_if_cancelled (cancellable))
* 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);
}
#ifndef G_OS_WIN32
static void
set_fd_nonblocking (int fd)
{
#ifdef F_GETFL
glong fcntl_flags;
fcntl_flags = fcntl (fd, F_GETFL);
#ifdef O_NONBLOCK
fcntl_flags |= O_NONBLOCK;
#else
fcntl_flags |= O_NDELAY;
#endif
fcntl (fd, F_SETFL, fcntl_flags);
#endif
}
static void
set_fd_close_exec (int fd)
{
int flags;
flags = fcntl (fd, F_GETFD, 0);
if (flags != -1 && (flags & FD_CLOEXEC) == 0)
{
flags |= FD_CLOEXEC;
fcntl (fd, F_SETFD, flags);
}
}
static void
g_cancellable_open_pipe (GCancellable *cancellable)
{
GCancellablePrivate *priv;
priv = cancellable->priv;
if (pipe (priv->cancel_pipe) == 0)
{
/* Make them nonblocking, just to be sure we don't block
* on errors and stuff
*/
set_fd_nonblocking (priv->cancel_pipe[0]);
set_fd_nonblocking (priv->cancel_pipe[1]);
set_fd_close_exec (priv->cancel_pipe[0]);
set_fd_close_exec (priv->cancel_pipe[1]);
if (priv->cancelled)
{
const char ch = 'x';
gssize c;
do
c = write (priv->cancel_pipe[1], &ch, 1);
while (c == -1 && errno == EINTR);
}
}
}
#endif
static void
g_cancellable_init (GCancellable *cancellable)
{
cancellable->priv = G_TYPE_INSTANCE_GET_PRIVATE (cancellable,
G_TYPE_CANCELLABLE,
GCancellablePrivate);
cancellable->priv->cancel_pipe[0] = -1;
cancellable->priv->cancel_pipe[1] = -1;
}
/**
* 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, but not 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
* cancllable can then be recieved 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_static_private_get (&current_cancellable);
l = g_slist_prepend (l, cancellable);
g_static_private_set (&current_cancellable, l, NULL);
}
/**
* 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_static_private_get (&current_cancellable);
g_return_if_fail (l != NULL);
g_return_if_fail (l->data == cancellable);
l = g_slist_delete_link (l, l);
g_static_private_set (&current_cancellable, l, NULL);
}
/**
* g_cancellable_get_current:
*
* Gets the top cancellable from the stack.
*
* Returns: 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_static_private_get (&current_cancellable);
if (l == NULL)
return NULL;
return G_CANCELLABLE (l->data);
}
/**
* g_cancellable_reset:
* @cancellable: a #GCancellable object.
*
* Resets @cancellable to its uncancelled state.
**/
void
g_cancellable_reset (GCancellable *cancellable)
{
GCancellablePrivate *priv;
g_return_if_fail (G_IS_CANCELLABLE (cancellable));
G_LOCK(cancellable);
priv = cancellable->priv;
while (priv->cancelled_running)
{
priv->cancelled_running_waiting = TRUE;
g_cond_wait (cancellable_cond,
g_static_mutex_get_mutex (& G_LOCK_NAME (cancellable)));
}
if (priv->cancelled)
{
/* Make sure we're not leaving old cancel state around */
#ifdef G_OS_WIN32
if (priv->event)
ResetEvent (priv->event);
#endif
if (priv->cancel_pipe[0] != -1)
{
gssize c;
char ch;
do
c = read (priv->cancel_pipe[0], &ch, 1);
while (c == -1 && errno == EINTR);
}
priv->cancelled = FALSE;
}
G_UNLOCK(cancellable);
}
/**
* g_cancellable_is_cancelled:
* @cancellable: 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: a #GCancellable object.
* @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)
{
GCancellablePrivate *priv;
int fd;
if (cancellable == NULL)
return -1;
priv = cancellable->priv;
#ifdef G_OS_WIN32
return -1;
#else
G_LOCK(cancellable);
if (priv->cancel_pipe[0] == -1)
g_cancellable_open_pipe (cancellable);
fd = priv->cancel_pipe[0];
if (fd != -1)
priv->fd_refcount++;
G_UNLOCK(cancellable);
#endif
return fd;
}
/**
* g_cancellable_make_pollfd:
* @cancellable: 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().
*
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* Returns: %TRUE if @pollfd was successfully initialized, %FALSE on
* failure to prepare the cancellable.
*
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* 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);
{
#ifdef G_OS_WIN32
GCancellablePrivate *priv;
priv = cancellable->priv;
G_LOCK(cancellable);
if (priv->event == NULL)
{
/* A manual reset anonymous event, starting unset */
priv->event = CreateEvent (NULL, TRUE, FALSE, NULL);
if (priv->event == NULL)
{
G_UNLOCK(cancellable);
return FALSE;
}
if (priv->cancelled)
SetEvent(priv->event);
}
priv->fd_refcount++;
G_UNLOCK(cancellable);
pollfd->fd = (gintptr)priv->event;
#else /* !G_OS_WIN32 */
int fd = g_cancellable_get_fd (cancellable);
if (fd == -1)
return FALSE;
pollfd->fd = fd;
#endif /* G_OS_WIN32 */
}
pollfd->events = G_IO_IN;
pollfd->revents = 0;
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.
*
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* 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_LOCK (cancellable);
priv->fd_refcount--;
if (priv->fd_refcount == 0)
g_cancellable_close_pipe (cancellable);
G_UNLOCK (cancellable);
}
/**
* g_cancellable_cancel:
* @cancellable: 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.
*
* 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 ||
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cancellable->priv->cancelled)
return;
priv = cancellable->priv;
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G_LOCK(cancellable);
if (priv->cancelled)
{
G_UNLOCK (cancellable);
return;
}
priv->cancelled = TRUE;
priv->cancelled_running = TRUE;
#ifdef G_OS_WIN32
if (priv->event)
SetEvent (priv->event);
#endif
if (priv->cancel_pipe[1] != -1)
{
const char ch = 'x';
gssize c;
do
c = write (priv->cancel_pipe[1], &ch, 1);
while (c == -1 && errno == EINTR);
}
G_UNLOCK(cancellable);
g_object_ref (cancellable);
g_signal_emit (cancellable, signals[CANCELLED], 0);
G_LOCK(cancellable);
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priv->cancelled_running = FALSE;
if (priv->cancelled_running_waiting)
g_cond_broadcast (cancellable_cond);
priv->cancelled_running_waiting = FALSE;
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G_UNLOCK(cancellable);
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g_object_unref (cancellable);
}
/**
* g_cancellable_connect:
* @cancellable: A #GCancellable.
* @callback: The #GCallback to connect.
* @data: Data to pass to @callback.
* @data_destroy_func: Free function for @data or %NULL.
*
* Convenience function to connect to the #GCancellable::cancelled
* signal. Also handles the race condition that may happen
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* 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.
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*
* Returns: The id of the signal handler or 0 if @cancellable has already
* been cancelled.
*
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* 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);
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G_LOCK (cancellable);
if (cancellable->priv->cancelled)
{
void (*_callback) (GCancellable *cancellable,
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gpointer user_data);
_callback = (void *)callback;
id = 0;
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_callback (cancellable, data);
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if (data_destroy_func)
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data_destroy_func (data);
}
else
{
id = g_signal_connect_data (cancellable, "cancelled",
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callback, data,
(GClosureNotify) data_destroy_func,
0);
}
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G_UNLOCK (cancellable);
return id;
}
/**
* g_cancellable_disconnect:
* @cancellable: 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
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* 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.
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*
* Since: 2.22
*/
void
g_cancellable_disconnect (GCancellable *cancellable,
gulong handler_id)
{
GCancellablePrivate *priv;
if (handler_id == 0 || cancellable == NULL)
return;
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G_LOCK (cancellable);
priv = cancellable->priv;
while (priv->cancelled_running)
{
priv->cancelled_running_waiting = TRUE;
g_cond_wait (cancellable_cond,
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g_static_mutex_get_mutex (& G_LOCK_NAME (cancellable)));
}
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g_signal_handler_disconnect (cancellable, handler_id);
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G_UNLOCK (cancellable);
}
#define __G_CANCELLABLE_C__
#include "gioaliasdef.c"