gio/gcancellable.c - third_party/glib - Git at Google

 /* 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 <fcntl.h>
 #include <gioerror.h>
 #ifdef G_OS_WIN32
 #include <io.h>
 #ifndef pipe
 #define pipe(fds) _pipe(fds, 4096, _O_BINARY)
 #endif
 #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 _GCancellable
 {
   GObject parent_instance;

   guint cancelled : 1;
   guint allocated_pipe : 1;
   guint cancelled_running : 1;
   guint cancelled_running_waiting : 1;
   int cancel_pipe[2];

 #ifdef G_OS_WIN32
   GIOChannel *read_channel;
 #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_finalize (GObject *object)
 {
   GCancellable *cancellable = G_CANCELLABLE (object);

   if (cancellable->cancel_pipe[0] != -1)
     close (cancellable->cancel_pipe[0]);

   if (cancellable->cancel_pipe[1] != -1)
     close (cancellable->cancel_pipe[1]);

 #ifdef G_OS_WIN32
   if (cancellable->read_channel)
     g_io_channel_unref (cancellable->read_channel);
 #endif

   G_OBJECT_CLASS (g_cancellable_parent_class)->finalize (object);
 }

 static void
 g_cancellable_class_init (GCancellableClass *klass)
 {
   GObjectClass *gobject_class = G_OBJECT_CLASS (klass);

   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);

 }

 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
 g_cancellable_open_pipe (GCancellable *cancellable)
 {
   if (pipe (cancellable->cancel_pipe) == 0)
     {
       /* Make them nonblocking, just to be sure we don't block
        * on errors and stuff
        */
       set_fd_nonblocking (cancellable->cancel_pipe[0]);
       set_fd_nonblocking (cancellable->cancel_pipe[1]);
     }
   else
     g_warning ("Failed to create pipe for GCancellable. Out of file descriptors?");
 }

 static void
 g_cancellable_init (GCancellable *cancellable)
 {
   cancellable->cancel_pipe[0] = -1;
   cancellable->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: optional #GCancellable object, %NULL to ignore.
  *
  * 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: optional #GCancellable object, %NULL to ignore.
  *
  * 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)
 {
   g_return_if_fail (G_IS_CANCELLABLE (cancellable));

   G_LOCK(cancellable);

   if (cancellable->cancelled_running)
     {
       g_critical ("Can't reset a cancellable during an active operation");
       G_UNLOCK(cancellable);
       return;
     }

   if (!cancellable->cancelled)
     {
       char ch;

     /* Make sure we're not leaving old cancel state around */

 #ifdef G_OS_WIN32
       if (cancellable->read_channel)
 	{
 	  gsize bytes_read;
 	  g_io_channel_read_chars (cancellable->read_channel, &ch, 1,
 				   &bytes_read, NULL);
 	}
       else
 #endif
       if (cancellable->cancel_pipe[0] != -1)
 	read (cancellable->cancel_pipe[0], &ch, 1);
       cancellable->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->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().
  *
  * 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)
 {
   int fd;
   if (cancellable == NULL)
     return -1;

   G_LOCK(cancellable);
   if (!cancellable->allocated_pipe)
     {
       cancellable->allocated_pipe = TRUE;
       g_cancellable_open_pipe (cancellable);
     }

   fd = cancellable->cancel_pipe[0];
   G_UNLOCK(cancellable);

   return fd;
 }

 /**
  * g_cancellable_make_pollfd:
  * @cancellable: a #GCancellable.
  * @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.
  *
  * 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().
  *
  **/
 void
 g_cancellable_make_pollfd (GCancellable *cancellable, GPollFD *pollfd)
 {
   g_return_if_fail (G_IS_CANCELLABLE (cancellable));
   g_return_if_fail (pollfd != NULL);

 #ifdef G_OS_WIN32
   if (!cancellable->read_channel)
     {
       int fd = g_cancellable_get_fd (cancellable);
       cancellable->read_channel = g_io_channel_win32_new_fd (fd);
       g_io_channel_set_buffered (cancellable->read_channel, FALSE);
       g_io_channel_set_flags (cancellable->read_channel,
 			      G_IO_FLAG_NONBLOCK, NULL);
       g_io_channel_set_encoding (cancellable->read_channel, NULL, NULL);
     }
   g_io_channel_win32_make_pollfd (cancellable->read_channel, G_IO_IN, pollfd);
   /* (We need to keep cancellable->read_channel around, because it's
    * keeping track of state related to the pollfd.)
    */
 #else /* !G_OS_WIN32 */
   pollfd->fd = g_cancellable_get_fd (cancellable);
   pollfd->events = G_IO_IN;
 #endif /* G_OS_WIN32 */
   pollfd->revents = 0;
 }

 /**
  * 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)
 {
   gboolean cancel;

   cancel = FALSE;

   G_LOCK(cancellable);
   if (cancellable != NULL &&
       !cancellable->cancelled)
     {
       char ch = 'x';
       cancel = TRUE;
       cancellable->cancelled = TRUE;
       cancellable->cancelled_running = TRUE;
       if (cancellable->cancel_pipe[1] != -1)
 	write (cancellable->cancel_pipe[1], &ch, 1);
     }
   G_UNLOCK(cancellable);

   if (cancel)
     {
       g_object_ref (cancellable);
       g_signal_emit (cancellable, signals[CANCELLED], 0);

       G_LOCK(cancellable);

       cancellable->cancelled_running = FALSE;
       if (cancellable->cancelled_running_waiting)
 	g_cond_broadcast (cancellable_cond);
       cancellable->cancelled_running_waiting = FALSE;

       G_UNLOCK(cancellable);

       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
  * 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.
  *
  * 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_LOCK (cancellable);

   if (cancellable->cancelled)
     {
       void (*_callback) (GCancellable *cancellable,
                          gpointer      user_data);

       _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_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 an cancellable instance similar to
  * g_signal_handler_disconnect() but ensures that once this
  * function returns the handler will not run anymore in any thread.
  *
  * 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)
 {
   if (handler_id == 0 ||  cancellable == NULL)
     return;

   G_LOCK (cancellable);
   while (cancellable->cancelled_running)
     {
       cancellable->cancelled_running_waiting = TRUE;
       g_cond_wait (cancellable_cond,
                    g_static_mutex_get_mutex (& G_LOCK_NAME (cancellable)));
     }

   g_signal_handler_disconnect (cancellable, handler_id);
   G_UNLOCK (cancellable);
 }

 #define __G_CANCELLABLE_C__
 #include "gioaliasdef.c"
	/* 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 <fcntl.h>
	#include <gioerror.h>
	#ifdef G_OS_WIN32
	#include <io.h>
	#ifndef pipe
	#define pipe(fds) _pipe(fds, 4096, _O_BINARY)
	#endif
	#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 _GCancellable
	{
	GObject parent_instance;

	guint cancelled : 1;
	guint allocated_pipe : 1;
	guint cancelled_running : 1;
	guint cancelled_running_waiting : 1;
	int cancel_pipe[2];

	#ifdef G_OS_WIN32
	GIOChannel *read_channel;
	#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_finalize (GObject *object)
	{
	GCancellable *cancellable = G_CANCELLABLE (object);

	if (cancellable->cancel_pipe[0] != -1)
	close (cancellable->cancel_pipe[0]);

	if (cancellable->cancel_pipe[1] != -1)
	close (cancellable->cancel_pipe[1]);

	#ifdef G_OS_WIN32
	if (cancellable->read_channel)
	g_io_channel_unref (cancellable->read_channel);
	#endif

	G_OBJECT_CLASS (g_cancellable_parent_class)->finalize (object);
	}

	static void
	g_cancellable_class_init (GCancellableClass *klass)
	{
	GObjectClass *gobject_class = G_OBJECT_CLASS (klass);

	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);

	}

	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
	g_cancellable_open_pipe (GCancellable *cancellable)
	{
	if (pipe (cancellable->cancel_pipe) == 0)
	{
	/* Make them nonblocking, just to be sure we don't block
	* on errors and stuff
	*/
	set_fd_nonblocking (cancellable->cancel_pipe[0]);
	set_fd_nonblocking (cancellable->cancel_pipe[1]);
	}
	else
	g_warning ("Failed to create pipe for GCancellable. Out of file descriptors?");
	}

	static void
	g_cancellable_init (GCancellable *cancellable)
	{
	cancellable->cancel_pipe[0] = -1;
	cancellable->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: optional #GCancellable object, %NULL to ignore.
	*
	* 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: optional #GCancellable object, %NULL to ignore.
	*
	* 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)
	{
	g_return_if_fail (G_IS_CANCELLABLE (cancellable));

	G_LOCK(cancellable);

	if (cancellable->cancelled_running)
	{
	g_critical ("Can't reset a cancellable during an active operation");
	G_UNLOCK(cancellable);
	return;
	}

	if (!cancellable->cancelled)
	{
	char ch;

	/* Make sure we're not leaving old cancel state around */

	#ifdef G_OS_WIN32
	if (cancellable->read_channel)
	{
	gsize bytes_read;
	g_io_channel_read_chars (cancellable->read_channel, &ch, 1,
	&bytes_read, NULL);
	}
	else
	#endif
	if (cancellable->cancel_pipe[0] != -1)
	read (cancellable->cancel_pipe[0], &ch, 1);
	cancellable->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->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().
	*
	* 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)
	{
	int fd;
	if (cancellable == NULL)
	return -1;

	G_LOCK(cancellable);
	if (!cancellable->allocated_pipe)
	{
	cancellable->allocated_pipe = TRUE;
	g_cancellable_open_pipe (cancellable);
	}

	fd = cancellable->cancel_pipe[0];
	G_UNLOCK(cancellable);

	return fd;
	}

	/**
	* g_cancellable_make_pollfd:
	* @cancellable: a #GCancellable.
	* @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.
	*
	* 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().
	*
	**/
	void
	g_cancellable_make_pollfd (GCancellable cancellable, GPollFD pollfd)
	{
	g_return_if_fail (G_IS_CANCELLABLE (cancellable));
	g_return_if_fail (pollfd != NULL);

	#ifdef G_OS_WIN32
	if (!cancellable->read_channel)
	{
	int fd = g_cancellable_get_fd (cancellable);
	cancellable->read_channel = g_io_channel_win32_new_fd (fd);
	g_io_channel_set_buffered (cancellable->read_channel, FALSE);
	g_io_channel_set_flags (cancellable->read_channel,
	G_IO_FLAG_NONBLOCK, NULL);
	g_io_channel_set_encoding (cancellable->read_channel, NULL, NULL);
	}
	g_io_channel_win32_make_pollfd (cancellable->read_channel, G_IO_IN, pollfd);
	/* (We need to keep cancellable->read_channel around, because it's
	* keeping track of state related to the pollfd.)
	*/
	#else /* !G_OS_WIN32 */
	pollfd->fd = g_cancellable_get_fd (cancellable);
	pollfd->events = G_IO_IN;
	#endif /* G_OS_WIN32 */
	pollfd->revents = 0;
	}

	/**
	* 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)
	{
	gboolean cancel;

	cancel = FALSE;

	G_LOCK(cancellable);
	if (cancellable != NULL &&
	!cancellable->cancelled)
	{
	char ch = 'x';
	cancel = TRUE;
	cancellable->cancelled = TRUE;
	cancellable->cancelled_running = TRUE;
	if (cancellable->cancel_pipe[1] != -1)
	write (cancellable->cancel_pipe[1], &ch, 1);
	}
	G_UNLOCK(cancellable);

	if (cancel)
	{
	g_object_ref (cancellable);
	g_signal_emit (cancellable, signals[CANCELLED], 0);

	G_LOCK(cancellable);

	cancellable->cancelled_running = FALSE;
	if (cancellable->cancelled_running_waiting)
	g_cond_broadcast (cancellable_cond);
	cancellable->cancelled_running_waiting = FALSE;

	G_UNLOCK(cancellable);

	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
	* 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.
	*
	* 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_LOCK (cancellable);

	if (cancellable->cancelled)
	{
	void (_callback) (GCancellable cancellable,
	gpointer user_data);

	_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_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 an cancellable instance similar to
	* g_signal_handler_disconnect() but ensures that once this
	* function returns the handler will not run anymore in any thread.
	*
	* 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)
	{
	if (handler_id == 0 \|\| cancellable == NULL)
	return;

	G_LOCK (cancellable);
	while (cancellable->cancelled_running)
	{
	cancellable->cancelled_running_waiting = TRUE;
	g_cond_wait (cancellable_cond,
	g_static_mutex_get_mutex (& G_LOCK_NAME (cancellable)));
	}

	g_signal_handler_disconnect (cancellable, handler_id);
	G_UNLOCK (cancellable);
	}

	#define __G_CANCELLABLE_C__
	#include "gioaliasdef.c"