glib/gio/gasyncresult.c

/* GIO - GLib Input, Output and Streaming Library
 *
 * Copyright (C) 2006-2007 Red Hat, Inc.
 *
 * SPDX-License-Identifier: LGPL-2.1-or-later
 *
 * 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 "gasyncresult.h"
#include "gsimpleasyncresult.h"
#include "glibintl.h"


/**
 * GAsyncResult:
 *
 * `GAsyncResult` provides a base class for implementing asynchronous function results.
 *
 * Asynchronous operations are broken up into two separate operations
 * which are chained together by a `GAsyncReadyCallback`. To begin
 * an asynchronous operation, provide a `GAsyncReadyCallback` to the
 * asynchronous function. This callback will be triggered when the
 * operation has completed, and must be run in a later iteration of
 * the thread-default main context (see
 * [method@GLib.MainContext.push_thread_default]) from where the operation was
 * initiated. It will be passed a `GAsyncResult` instance filled with the
 * details of the operation's success or failure, the object the asynchronous
 * function was started for and any error codes returned. The asynchronous
 * callback function is then expected to call the corresponding `_finish()`
 * function, passing the object the function was called for, the
 * `GAsyncResult` instance, and (optionally) an @error to grab any
 * error conditions that may have occurred.
 *
 * The `_finish()` function for an operation takes the generic result
 * (of type `GAsyncResult`) and returns the specific result that the
 * operation in question yields (e.g. a [class@Gio.FileEnumerator] for a
 * "enumerate children" operation). If the result or error status of the
 * operation is not needed, there is no need to call the `_finish()`
 * function; GIO will take care of cleaning up the result and error
 * information after the `GAsyncReadyCallback` returns. You can pass
 * `NULL` for the `GAsyncReadyCallback` if you don't need to take any
 * action at all after the operation completes. Applications may also
 * take a reference to the `GAsyncResult` and call `_finish()` later;
 * however, the `_finish()` function may be called at most once.
 *
 * Example of a typical asynchronous operation flow:
 *
 * ```c
 * void _theoretical_frobnitz_async (Theoretical         *t,
 *                                   GCancellable        *c,
 *                                   GAsyncReadyCallback  cb,
 *                                   gpointer             u);
 *
 * gboolean _theoretical_frobnitz_finish (Theoretical   *t,
 *                                        GAsyncResult  *res,
 *                                        GError       **e);
 *
 * static void
 * frobnitz_result_func (GObject      *source_object,
 *			 GAsyncResult *res,
 *			 gpointer      user_data)
 * {
 *   gboolean success = FALSE;
 *
 *   success = _theoretical_frobnitz_finish (source_object, res, NULL);
 *
 *   if (success)
 *     g_printf ("Hurray!\n");
 *   else
 *     g_printf ("Uh oh!\n");
 *
 *   ...
 *
 * }
 *
 * int main (int argc, void *argv[])
 * {
 *    ...
 *
 *    _theoretical_frobnitz_async (theoretical_data,
 *                                 NULL,
 *                                 frobnitz_result_func,
 *                                 NULL);
 *
 *    ...
 * }
 * ```
 *
 * The callback for an asynchronous operation is called only once, and is
 * always called, even in the case of a cancelled operation. On cancellation
 * the result is a `G_IO_ERROR_CANCELLED` error.
 *
 * ## I/O Priority
 *
 * Many I/O-related asynchronous operations have a priority parameter,
 * which is used in certain cases to determine the order in which
 * operations are executed. They are not used to determine system-wide
 * I/O scheduling. Priorities are integers, with lower numbers indicating
 * higher priority. It is recommended to choose priorities between
 * `G_PRIORITY_LOW` and `G_PRIORITY_HIGH`, with `G_PRIORITY_DEFAULT`
 * as a default.
 */

typedef GAsyncResultIface GAsyncResultInterface;
G_DEFINE_INTERFACE (GAsyncResult, g_async_result, G_TYPE_OBJECT)

static void
g_async_result_default_init (GAsyncResultInterface *iface)
{
}

/**
 * g_async_result_get_user_data:
 * @res: a #GAsyncResult.
 *
 * Gets the user data from a #GAsyncResult.
 *
 * Returns: (transfer full): the user data for @res.
 **/
gpointer
g_async_result_get_user_data (GAsyncResult *res)
{
  GAsyncResultIface *iface;

  g_return_val_if_fail (G_IS_ASYNC_RESULT (res), NULL);

  iface = G_ASYNC_RESULT_GET_IFACE (res);

  return (* iface->get_user_data) (res);
}

/**
 * g_async_result_get_source_object:
 * @res: a #GAsyncResult
 *
 * Gets the source object from a #GAsyncResult.
 *
 * Returns: (transfer full) (nullable): a new reference to the source
 *    object for the @res, or %NULL if there is none.
 */
GObject *
g_async_result_get_source_object (GAsyncResult *res)
{
  GAsyncResultIface *iface;

  g_return_val_if_fail (G_IS_ASYNC_RESULT (res), NULL);

  iface = G_ASYNC_RESULT_GET_IFACE (res);

  return (* iface->get_source_object) (res);
}

/**
 * g_async_result_legacy_propagate_error:
 * @res: a #GAsyncResult
 * @error: (out): a location to propagate the error to.
 *
 * If @res is a #GSimpleAsyncResult, this is equivalent to
 * g_simple_async_result_propagate_error(). Otherwise it returns
 * %FALSE.
 *
 * This can be used for legacy error handling in async *_finish()
 * wrapper functions that traditionally handled #GSimpleAsyncResult
 * error returns themselves rather than calling into the virtual method.
 * This should not be used in new code; #GAsyncResult errors that are
 * set by virtual methods should also be extracted by virtual methods,
 * to enable subclasses to chain up correctly.
 *
 * Returns: %TRUE if @error is has been filled in with an error from
 *   @res, %FALSE if not.
 *
 * Since: 2.34
 **/
gboolean
g_async_result_legacy_propagate_error (GAsyncResult  *res,
				       GError       **error)
{
  /* This doesn't use a vmethod, because it's only for code that used
   * to use GSimpleAsyncResult. (But it's a GAsyncResult method so
   * that callers don't need to worry about GSimpleAsyncResult
   * deprecation warnings in the future.)
   */

  G_GNUC_BEGIN_IGNORE_DEPRECATIONS
  if (G_IS_SIMPLE_ASYNC_RESULT (res))
    {
      return g_simple_async_result_propagate_error (G_SIMPLE_ASYNC_RESULT (res),
						    error);
    }
  else
    return FALSE;
  G_GNUC_END_IGNORE_DEPRECATIONS
}

/**
 * g_async_result_is_tagged:
 * @res: a #GAsyncResult
 * @source_tag: an application-defined tag
 *
 * Checks if @res has the given @source_tag (generally a function
 * pointer indicating the function @res was created by).
 *
 * Returns: %TRUE if @res has the indicated @source_tag, %FALSE if
 *   not.
 *
 * Since: 2.34
 **/
gboolean
g_async_result_is_tagged (GAsyncResult  *res,
			  gpointer       source_tag)
{
  GAsyncResultIface *iface;

  g_return_val_if_fail (G_IS_ASYNC_RESULT (res), FALSE);

  iface = G_ASYNC_RESULT_GET_IFACE (res);

  if (!iface->is_tagged)
    return FALSE;

  return (* iface->is_tagged) (res, source_tag);
}