GI.Gio.Objects.SimpleAsyncResult

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

SimpleAsyncResult implements AsyncResult.

GSimpleAsyncResult handles GAsyncReadyCallbacks, 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 SimpleAsyncResult, call simpleAsyncResultNew. If the result needs to be created for a GError, use simpleAsyncResultNewFromError or g_simple_async_result_new_take_error(). If a GError is not available (e.g. the asynchronous operation's doesn't take a GError argument), but the result still needs to be created for an error condition, use g_simple_async_result_new_error() (or g_simple_async_result_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 simpleAsyncResultPropagateError.

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

GSimpleAsyncResult can integrate into GLib's event loop, MainLoop, or it can use GThreads. simpleAsyncResultComplete will finish an I/O task directly from the point where it is called. simpleAsyncResultCompleteInIdle will finish it from an idle handler in the [thread-default main context][g-main-context-push-thread-default] where the SimpleAsyncResult was created. g_simple_async_result_run_in_thread() will run the job in a separate thread and then use simpleAsyncResultCompleteInIdle to deliver the result.

To set the results of an asynchronous function, g_simple_async_result_set_op_res_gpointer(), simpleAsyncResultSetOpResGboolean, and simpleAsyncResultSetOpResGssize are provided, setting the operation's result to a gpointer, gboolean, or gssize, respectively.

Likewise, to get the result of an asynchronous function, g_simple_async_result_get_op_res_gpointer(), simpleAsyncResultGetOpResGboolean, and simpleAsyncResultGetOpResGssize 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:

C code

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);
}

Exported types

newtype SimpleAsyncResult

Memory-managed wrapper type.

Constructors

SimpleAsyncResult (ManagedPtr SimpleAsyncResult)

Instances

Eq SimpleAsyncResult

Defined in GI.Gio.Objects.SimpleAsyncResult

Methods

(==) :: SimpleAsyncResult -> SimpleAsyncResult -> Bool

(/=) :: SimpleAsyncResult -> SimpleAsyncResult -> Bool

GObject SimpleAsyncResult

Defined in GI.Gio.Objects.SimpleAsyncResult

Methods

gobjectType :: IO GType

IsGValue SimpleAsyncResult

Convert SimpleAsyncResult to and from GValue with toGValue and fromGValue.

Defined in GI.Gio.Objects.SimpleAsyncResult

Methods

toGValue :: SimpleAsyncResult -> IO GValue

fromGValue :: GValue -> IO SimpleAsyncResult

HasParentTypes SimpleAsyncResult

Defined in GI.Gio.Objects.SimpleAsyncResult

type ParentTypes SimpleAsyncResult

Defined in GI.Gio.Objects.SimpleAsyncResult

type ParentTypes SimpleAsyncResult = '[Object, AsyncResult]

class (GObject o, IsDescendantOf SimpleAsyncResult o) => IsSimpleAsyncResult o

Type class for types which can be safely cast to SimpleAsyncResult, for instance with toSimpleAsyncResult.

Instances

(GObject o, IsDescendantOf SimpleAsyncResult o) => IsSimpleAsyncResult o

Defined in GI.Gio.Objects.SimpleAsyncResult

toSimpleAsyncResult :: (MonadIO m, IsSimpleAsyncResult o) => o -> m SimpleAsyncResult

Cast to SimpleAsyncResult, for types for which this is known to be safe. For general casts, use castTo.

noSimpleAsyncResult :: Maybe SimpleAsyncResult

A convenience alias for Nothing :: Maybe SimpleAsyncResult.

Methods

Overloaded methods

complete

simpleAsyncResultComplete

Arguments

:: (HasCallStack, MonadIO m, IsSimpleAsyncResult a)

=> a

simple: a SimpleAsyncResult.

-> m ()

Deprecated: (Since version 2.46)Use Task instead.

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 simpleAsyncResultCompleteInIdle.

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

completeInIdle

simpleAsyncResultCompleteInIdle

Arguments

:: (HasCallStack, MonadIO m, IsSimpleAsyncResult a)

=> a

simple: a SimpleAsyncResult.

-> m ()

Deprecated: (Since version 2.46)Use Task instead.

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.

getOpResGboolean

simpleAsyncResultGetOpResGboolean

Arguments

:: (HasCallStack, MonadIO m, IsSimpleAsyncResult a)

=> a

simple: a SimpleAsyncResult.

-> m Bool

Returns: True if the operation's result was True, False if the operation's result was False.

Deprecated: (Since version 2.46)Use Task and taskPropagateBoolean instead.

Gets the operation result boolean from within the asynchronous result.

getOpResGssize

simpleAsyncResultGetOpResGssize

Arguments

:: (HasCallStack, MonadIO m, IsSimpleAsyncResult a)

=> a

simple: a SimpleAsyncResult.

-> m Int64

Returns: a gssize returned from the asynchronous function.

Deprecated: (Since version 2.46)Use Task and taskPropagateInt instead.

Gets a gssize from the asynchronous result.

isValid

simpleAsyncResultIsValid

Arguments

:: (HasCallStack, MonadIO m, IsAsyncResult a, IsObject b)

=> a

result: the AsyncResult passed to the _finish function.

-> Maybe b

source: the Object passed to the _finish function.

-> Ptr ()

sourceTag: the asynchronous function.

-> m Bool

Returns: TRUE if all checks passed or FALSE if any failed.

Deprecated: (Since version 2.46)Use Task and taskIsValid instead.

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, sourceTag is checked to ensure that it is equal to the sourceTag argument given to simpleAsyncResultNew (which, by convention, is a pointer to the _async function corresponding to the _finish function from which this function is called). (Alternatively, if either sourceTag or result's source tag is Nothing, then the source tag check is skipped.)

Since: 2.20

new

simpleAsyncResultNew

Arguments

:: (HasCallStack, MonadIO m, IsObject a)

=> Maybe a

sourceObject: a Object, or Nothing.

-> Maybe AsyncReadyCallback

callback: a AsyncReadyCallback.

-> Ptr ()

sourceTag: the asynchronous function.

-> m SimpleAsyncResult

Returns: a SimpleAsyncResult.

Deprecated: (Since version 2.46)Use taskNew instead.

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 sourceTag.

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

newFromError

simpleAsyncResultNewFromError

Arguments

:: (HasCallStack, MonadIO m, IsObject a)

=> Maybe a

sourceObject: a Object, or Nothing.

-> Maybe AsyncReadyCallback

callback: a AsyncReadyCallback.

-> GError

error: a GError

-> m SimpleAsyncResult

Returns: a SimpleAsyncResult.

Deprecated: (Since version 2.46)Use taskNew and taskReturnError instead.

Creates a SimpleAsyncResult from an error condition.

propagateError

simpleAsyncResultPropagateError

Arguments

:: (HasCallStack, MonadIO m, IsSimpleAsyncResult a)

=> a

simple: a SimpleAsyncResult.

-> m ()

(Can throw GError)

Deprecated: (Since version 2.46)Use Task instead.

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

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

setCheckCancellable

simpleAsyncResultSetCheckCancellable

Arguments

:: (HasCallStack, MonadIO m, IsSimpleAsyncResult a, IsCancellable b)

=> a

simple: a SimpleAsyncResult

-> Maybe b

checkCancellable: a Cancellable to check, or Nothing to unset

-> m ()

Deprecated: (Since version 2.46)Use Task instead.

Sets a Cancellable to check before dispatching results.

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

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 simpleAsyncResultSetHandleCancellation function.

Since: 2.32

setFromError

simpleAsyncResultSetFromError

Arguments

:: (HasCallStack, MonadIO m, IsSimpleAsyncResult a)

=> a

simple: a SimpleAsyncResult.

-> GError

error: GError.

-> m ()

Deprecated: (Since version 2.46)Use Task and taskReturnError instead.

Sets the result from a GError.

setHandleCancellation

simpleAsyncResultSetHandleCancellation

Arguments

:: (HasCallStack, MonadIO m, IsSimpleAsyncResult a)

=> a

simple: a SimpleAsyncResult.

-> Bool

handleCancellation: a Bool.

-> m ()

Deprecated: (Since version 2.46)

Sets whether to handle cancellation within the asynchronous operation.

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

setOpResGboolean

simpleAsyncResultSetOpResGboolean

Arguments

:: (HasCallStack, MonadIO m, IsSimpleAsyncResult a)

=> a

simple: a SimpleAsyncResult.

-> Bool

opRes: a Bool.

-> m ()

Deprecated: (Since version 2.46)Use Task and taskReturnBoolean instead.

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

setOpResGssize

simpleAsyncResultSetOpResGssize

Arguments

:: (HasCallStack, MonadIO m, IsSimpleAsyncResult a)

=> a

simple: a SimpleAsyncResult.

-> Int64

opRes: a gssize.

-> m ()

Deprecated: (Since version 2.46)Use Task and taskReturnInt instead.

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