gio.simple_async_result

As of GLib 2.46, gio.simple_async_result.SimpleAsyncResult is deprecated in favor of gio.task.Task, which provides a simpler API.

gio.simple_async_result.SimpleAsyncResult implements gio.async_result.AsyncResult.

gio.simple_async_result.SimpleAsyncResult handles gio.types.AsyncReadyCallbacks, error reporting, operation cancellation and the final state of an operation, completely transparent to the application. Results can be returned as a pointer e.g. for functions that return data that is collected asynchronously, a boolean value for checking the success or failure of an operation, or a gssize for operations which return the number of bytes modified by the operation; all of the simple return cases are covered.

Most of the time, an application will not need to know of the details of this API; it is handled transparently, and any necessary operations are handled by gio.async_result.AsyncResult’s interface. However, if implementing a new GIO module, for writing language bindings, or for complex applications that need better control of how asynchronous operations are completed, it is important to understand this functionality.

gio.simple_async_result.SimpleAsyncResults are tagged with the calling function to ensure that asynchronous functions and their finishing functions are used together correctly.

To create a new gio.simple_async_result.SimpleAsyncResult, call gio.simple_async_result.SimpleAsyncResult.new_. If the result needs to be created for a glib.error.ErrorWrap, use gio.simple_async_result.SimpleAsyncResult.newFromError or gio.simple_async_result.SimpleAsyncResult.newTakeError. If a glib.error.ErrorWrap is not available (e.g. the asynchronous operation doesn’t take a glib.error.ErrorWrap argument), but the result still needs to be created for an error condition, use gio.simple_async_result.SimpleAsyncResult.newError (or gio.simple_async_result.SimpleAsyncResult.setErrorVa if your application or binding requires passing a variable argument list directly), and the error can then be propagated through the use of gio.simple_async_result.SimpleAsyncResult.propagateError.

An asynchronous operation can be made to ignore a cancellation event by calling gio.simple_async_result.SimpleAsyncResult.setHandleCancellation with a gio.simple_async_result.SimpleAsyncResult for the operation and FALSE. This is useful for operations that are dangerous to cancel, such as close (which would cause a leak if cancelled before being run).

gio.simple_async_result.SimpleAsyncResult can integrate into GLib’s event loop, glib.main_loop.MainLoop, or it can use glib.thread.Threads. gio.simple_async_result.SimpleAsyncResult.complete will finish an I/O task directly from the point where it is called. gio.simple_async_result.SimpleAsyncResult.completeInIdle will finish it from an idle handler in the thread-default main context (see glib.main_context.MainContext.pushThreadDefault) where the gio.simple_async_result.SimpleAsyncResult was created. gio.simple_async_result.SimpleAsyncResult.runInThread will run the job in a separate thread and then use gio.simple_async_result.SimpleAsyncResult.completeInIdle to deliver the result.

To set the results of an asynchronous function, gio.simple_async_result.SimpleAsyncResult.setOpResGpointer, gio.simple_async_result.SimpleAsyncResult.setOpResGboolean, and gio.simple_async_result.SimpleAsyncResult.setOpResGssize are provided, setting the operation's result to a xlib.types.void*, gboolean, or gssize, respectively.

Likewise, to get the result of an asynchronous function, gio.simple_async_result.SimpleAsyncResult.getOpResGpointer, gio.simple_async_result.SimpleAsyncResult.getOpResGboolean, and gio.simple_async_result.SimpleAsyncResult.getOpResGssize are provided, getting the operation’s result as a xlib.types.void*, gboolean, and gssize, respectively.

For the details of the requirements implementations must respect, see gio.async_result.AsyncResult. A typical implementation of an asynchronous operation using gio.simple_async_result.SimpleAsyncResult looks something like this:

static void
baked_cb (Cake    *cake,
          gpointer user_data)
{
  // In this example, this callback is not given a reference to the cake,
  // so the GSimpleAsyncResult has to take a reference to it.
  GSimpleAsyncResult *result = user_data;

  if (cake == NULL)
    g_simple_async_result_set_error (result,
                                     BAKER_ERRORS,
                                     BAKER_ERROR_NO_FLOUR,
                                     "Go to the supermarket");
  else
    g_simple_async_result_set_op_res_gpointer (result,
                                               g_object_ref (cake),
                                               g_object_unref);

  // In this example, we assume that baked_cb is called as a callback from
  // the mainloop, so it's safe to complete the operation synchronously here.
  // If, however, _baker_prepare_cake () might call its callback without
  // first returning to the mainloop — inadvisable, but some APIs do so —
  // we would need to use g_simple_async_result_complete_in_idle().
  g_simple_async_result_complete (result);
  g_object_unref (result);
}

void
baker_bake_cake_async (Baker              *self,
                       guint               radius,
                       GAsyncReadyCallback callback,
                       gpointer            user_data)
{
  GSimpleAsyncResult *simple;
  Cake               *cake;

  if (radius < 3)
    {
      g_simple_async_report_error_in_idle (G_OBJECT (self),
                                           callback,
                                           user_data,
                                           BAKER_ERRORS,
                                           BAKER_ERROR_TOO_SMALL,
                                           "%ucm radius cakes are silly",
                                           radius);
      return;
    }

  simple = g_simple_async_result_new (G_OBJECT (self),
                                      callback,
                                      user_data,
                                      baker_bake_cake_async);
  cake = _baker_get_cached_cake (self, radius);

  if (cake != NULL)
    {
      g_simple_async_result_set_op_res_gpointer (simple,
                                                 g_object_ref (cake),
                                                 g_object_unref);
      g_simple_async_result_complete_in_idle (simple);
      g_object_unref (simple);
      // Drop the reference returned by _baker_get_cached_cake();
      // the GSimpleAsyncResult has taken its own reference.
      g_object_unref (cake);
      return;
    }

  _baker_prepare_cake (self, radius, baked_cb, simple);
}

Cake *
baker_bake_cake_finish (Baker        *self,
                        GAsyncResult *result,
                        GError      **error)
{
  GSimpleAsyncResult *simple;
  Cake               *cake;

  g_return_val_if_fail (g_simple_async_result_is_valid (result,
                                                        G_OBJECT (self),
                                                        baker_bake_cake_async),
                        NULL);

  simple = (GSimpleAsyncResult *) result;

  if (g_simple_async_result_propagate_error (simple, error))
    return NULL;

  cake = CAKE (g_simple_async_result_get_op_res_gpointer (simple));
  return g_object_ref (cake);
}

Fluent builder implementation template for gio.simple_async_result.SimpleAsyncResult

Fluent builder for gio.simple_async_result.SimpleAsyncResult