Gio.SimpleAsyncResult¶

class — extends GObject.Object, AsyncResult

As of GLib 2.46, GSimpleAsyncResult is deprecated in favor of Task, which provides a simpler API.

GSimpleAsyncResult implements AsyncResult.

GSimpleAsyncResult handles 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 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.

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

To create a new GSimpleAsyncResult, call SimpleAsyncResult.new. If the result needs to be created for a GError, use SimpleAsyncResult.new_from_error or SimpleAsyncResult.new_take_error. If a GError is not available (e.g. the asynchronous operation doesn’t take a GError argument), but the result still needs to be created for an error condition, use SimpleAsyncResult.new_error (or SimpleAsyncResult.set_error_va if your application or binding requires passing a variable argument list directly), and the error can then be propagated through the use of SimpleAsyncResult.propagate_error.

An asynchronous operation can be made to ignore a cancellation event by calling SimpleAsyncResult.set_handle_cancellation with a GSimpleAsyncResult 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).

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

To set the results of an asynchronous function, SimpleAsyncResult.set_op_res_gpointer, SimpleAsyncResult.set_op_res_gboolean, and SimpleAsyncResult.set_op_res_gssize are provided, setting the operation's result to a gpointer, gboolean, or gssize, respectively.

Likewise, to get the result of an asynchronous function, SimpleAsyncResult.get_op_res_gpointer, SimpleAsyncResult.get_op_res_gboolean, and SimpleAsyncResult.get_op_res_gssize are provided, getting the operation’s result as a gpointer, gboolean, and gssize, respectively.

For the details of the requirements implementations must respect, see AsyncResult. A typical implementation of an asynchronous operation using GSimpleAsyncResult 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);
}

Constructors¶

new¶

@classmethod
def new(cls, source_object: GObject.Object | None = ..., callback: Callable[[SimpleAsyncResult | None, AsyncResult], None] | None = ..., source_tag: int | None = ...) -> SimpleAsyncResult

:::warning Deprecated since 2.46 This API is deprecated. :::

Creates a SimpleAsyncResult.

The common convention is to create the SimpleAsyncResult in the function that starts the asynchronous operation and use that same function as the source_tag.

If your operation supports cancellation with Cancellable (which it probably should) then you should provide the user's cancellable to SimpleAsyncResult.set_check_cancellable immediately after this function returns.

Parameters:

source_object — a GObject.Object, or None.
callback — a GAsyncReadyCallback.
source_tag — the asynchronous function.

new_from_error¶

@classmethod
def new_from_error(cls, source_object: GObject.Object | None, callback: Callable[[SimpleAsyncResult | None, AsyncResult], None] | None, error: GLib.Error) -> SimpleAsyncResult

:::warning Deprecated since 2.46 This API is deprecated. :::

Creates a SimpleAsyncResult from an error condition.

Parameters:

source_object — a GObject.Object, or None.
callback — a GAsyncReadyCallback.
error — a GLib.Error

Methods¶

complete¶

def complete(self) -> None

:::warning Deprecated since 2.46 This API is deprecated. :::

Completes an asynchronous I/O job immediately. Must be called in the thread where the asynchronous result was to be delivered, as it invokes the callback directly. If you are in a different thread use SimpleAsyncResult.complete_in_idle.

Calling this function takes a reference to simple for as long as is needed to complete the call.

complete_in_idle¶

def complete_in_idle(self) -> None

:::warning Deprecated since 2.46 This API is deprecated. :::

Completes an asynchronous function in an idle handler in the thread-default main context (see GLib.MainContext.push_thread_default) of the thread that simple was initially created in (and re-pushes that context around the invocation of the callback).

Calling this function takes a reference to simple for as long as is needed to complete the call.

get_op_res_gboolean¶

def get_op_res_gboolean(self) -> bool

:::warning Deprecated since 2.46 This API is deprecated. :::

Gets the operation result boolean from within the asynchronous result.

get_op_res_gssize¶

def get_op_res_gssize(self) -> int

:::warning Deprecated since 2.46 This API is deprecated. :::

Gets a gssize from the asynchronous result.

propagate_error¶

def propagate_error(self) -> bool

:::warning Deprecated since 2.46 This API is deprecated. :::

Propagates an error from within the simple asynchronous result to a given destination.

If the Cancellable given to a prior call to SimpleAsyncResult.set_check_cancellable is cancelled then this function will return True with dest set appropriately.

set_check_cancellable¶

def set_check_cancellable(self, check_cancellable: Cancellable | None = ...) -> None

:::warning Deprecated since 2.46 This API is deprecated. :::

Sets a Cancellable to check before dispatching results.

This function has one very specific purpose: the provided cancellable is checked at the time of SimpleAsyncResult.propagate_error If it is cancelled, these functions will return an "Operation was cancelled" error (IOErrorEnum.CANCELLED).

Implementors of cancellable asynchronous functions should use this in order to provide a guarantee to their callers that cancelling an async operation will reliably result in an error being returned for that operation (even if a positive result for the operation has already been sent as an idle to the main context to be dispatched).

The checking described above is done regardless of any call to the unrelated SimpleAsyncResult.set_handle_cancellation function.

Parameters:

check_cancellable — a Cancellable to check, or None to unset

set_from_error¶

def set_from_error(self, error: GLib.Error) -> None

:::warning Deprecated since 2.46 This API is deprecated. :::

Sets the result from a GLib.Error.

Parameters:

error — GLib.Error.

set_handle_cancellation¶

def set_handle_cancellation(self, handle_cancellation: bool) -> None

:::warning Deprecated since 2.46 This API is deprecated. :::

Sets whether to handle cancellation within the asynchronous operation.

This function has nothing to do with SimpleAsyncResult.set_check_cancellable. It only refers to the Cancellable passed to g_simple_async_result_run_in_thread().

Parameters:

handle_cancellation — a #gboolean.

set_op_res_gboolean¶

def set_op_res_gboolean(self, op_res: bool) -> None

:::warning Deprecated since 2.46 This API is deprecated. :::

Sets the operation result to a boolean within the asynchronous result.

Parameters:

op_res — a #gboolean.

set_op_res_gssize¶

def set_op_res_gssize(self, op_res: int) -> None

:::warning Deprecated since 2.46 This API is deprecated. :::

Sets the operation result within the asynchronous result to the given op_res.

Parameters:

op_res — a #gssize.

Static functions¶

is_valid¶

@staticmethod
def is_valid(result: AsyncResult, source: GObject.Object | None = ..., source_tag: int | None = ...) -> bool

:::warning Deprecated since 2.46 This API is deprecated. :::

Ensures that the data passed to the _finish function of an async operation is consistent. Three checks are performed.

First, result is checked to ensure that it is really a SimpleAsyncResult. Second, source is checked to ensure that it matches the source object of result. Third, source_tag is checked to ensure that it is equal to the source_tag argument given to SimpleAsyncResult.new (which, by convention, is a pointer to the _async function corresponding to the _finish function from which this function is called). (Alternatively, if either source_tag or result's source tag is None, then the source tag check is skipped.)

Parameters:

result — the AsyncResult passed to the _finish function.
source — the GObject.Object passed to the _finish function.
source_tag — the asynchronous function.