SimpleAsyncResult

class SimpleAsyncResult(**properties: Any)

Superclasses: Object

Implemented Interfaces: AsyncResult

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

GSimpleAsyncResult implements AsyncResult.

GSimpleAsyncResult handles AsyncReadyCallback’s, 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.

GSimpleAsyncResult’s 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 new. If the result needs to be created for a GError, use new_from_error or 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 new_error (or 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 propagate_error.

An asynchronous operation can be made to ignore a cancellation event by calling 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, MainLoop, or it can use Thread’s. complete will finish an I/O task directly from the point where it is called. complete_in_idle will finish it from an idle handler in the thread-default main context (see push_thread_default) where the GSimpleAsyncResult was created. run_in_thread will run the job in a separate thread and then use complete_in_idle to deliver the result.

To set the results of an asynchronous function, set_op_res_gpointer, set_op_res_gboolean, and 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, get_op_res_gpointer, get_op_res_gboolean, and 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 :func:`~gi.repository.Gio.SimpleAsyncResult.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

class SimpleAsyncResult

classmethod new(source_object: Object | None, callback: Callable[[...], None] | None, source_tag: None, *user_data: Any) → SimpleAsyncResult

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 set_check_cancellable() immediately after this function returns.

Deprecated since version 2.46: Use new() instead.

Parameters:

source_object – a Object, or None.
callback – a AsyncReadyCallback.
source_tag – the asynchronous function.
user_data – user data passed to callback.

classmethod new_from_error(source_object: Object | None, callback: Callable[[...], None] | None, error: GError, *user_data: Any) → SimpleAsyncResult

Creates a SimpleAsyncResult from an error condition.

Deprecated since version 2.46: Use new() and return_error() instead.

Parameters:

source_object – a Object, or None.
callback – a AsyncReadyCallback.
error – a Error
user_data – user data passed to callback.

Methods

class SimpleAsyncResult

complete() → None

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 complete_in_idle().

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

Deprecated since version 2.46: Use Task instead.

complete_in_idle() → None

Completes an asynchronous function in an idle handler in the [thread-default main context][g-main-context-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.

Deprecated since version 2.46: Use Task instead.

get_op_res_gboolean() → bool: Gets the operation result boolean from within the asynchronous result.

Deprecated since version 2.46: Use Task and propagate_boolean() instead.

get_op_res_gssize() → int: Gets a gssize from the asynchronous result.

Deprecated since version 2.46: Use Task and propagate_int() instead.

is_valid(result: AsyncResult, source: Object | None, source_tag: None) → bool

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 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.)

Added in version 2.20.

Deprecated since version 2.46: Use Task and is_valid() instead.

Parameters:

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

propagate_error() → bool

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

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

Deprecated since version 2.46: Use Task instead.

set_check_cancellable(check_cancellable: Cancellable | None = None) → None

Sets a Cancellable to check before dispatching results.

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

Added in version 2.32.

Deprecated since version 2.46: Use Task instead.

Parameters:: check_cancellable – a Cancellable to check, or None to unset

set_from_error(error: GError) → None

Sets the result from a Error.

Deprecated since version 2.46: Use Task and return_error() instead.

Parameters:: error – Error.

set_handle_cancellation(handle_cancellation: bool) → None

Sets whether to handle cancellation within the asynchronous operation.

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

Deprecated since version 2.46: Please do not use it in newly written code

Parameters:: handle_cancellation – a gboolean.

set_op_res_gboolean(op_res: bool) → None

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

Deprecated since version 2.46: Use Task and return_boolean() instead.

Parameters:: op_res – a gboolean.

set_op_res_gssize(op_res: int) → None

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

Deprecated since version 2.46: Use Task and return_int() instead.

Parameters:: op_res – a gssize.