Commit 48040944 authored by Allison Karlitskaya's avatar Allison Karlitskaya

GSimpleAsyncResult: support reliable cancellation

Add a function g_simple_async_result_set_check_cancellable() to provide
a GCancellable that is checked for being cancelled during the call to
g_simple_async_result_propagate_error().

This gives asynchronous operation implementations an easy way to
provide reliable cancellation of those operations -- even in the case
that a positive result has occured and is pending dispatch at the time
the operation is cancelled.

https://bugzilla.gnome.org/show_bug.cgi?id=672013
parent 53b1afba
......@@ -1211,6 +1211,7 @@ g_simple_async_result_new
g_simple_async_result_new_error
g_simple_async_result_new_from_error
g_simple_async_result_new_take_error
g_simple_async_result_set_check_cancellable
g_simple_async_result_set_op_res_gpointer
g_simple_async_result_get_op_res_gpointer
g_simple_async_result_set_op_res_gssize
......
......@@ -596,6 +596,7 @@ g_simple_async_result_new
g_simple_async_result_new_error
g_simple_async_result_new_from_error
g_simple_async_result_new_take_error
g_simple_async_result_set_check_cancellable
g_simple_async_result_set_op_res_gpointer
g_simple_async_result_get_op_res_gpointer
g_simple_async_result_set_op_res_gssize
......
......@@ -227,6 +227,7 @@ struct _GSimpleAsyncResult
GError *error;
gboolean failed;
gboolean handle_cancellation;
GCancellable *check_cancellable;
gpointer source_tag;
......@@ -268,6 +269,9 @@ g_simple_async_result_finalize (GObject *object)
if (simple->source_object)
g_object_unref (simple->source_object);
if (simple->check_cancellable)
g_object_unref (simple->check_cancellable);
g_main_context_unref (simple->context);
clear_op_res (simple);
......@@ -303,6 +307,15 @@ g_simple_async_result_init (GSimpleAsyncResult *simple)
*
* Creates a #GSimpleAsyncResult.
*
* The common convention is to create the #GSimpleAsyncResult in the
* function that starts the asynchronous operation and use that same
* function as the @source_tag.
*
* If your operation supports cancellation with #GCancellable (which it
* probably should) then you should provide the user's cancellable to
* g_simple_async_result_set_check_cancellable() immediately after
* this function returns.
*
* Returns: a #GSimpleAsyncResult.
**/
GSimpleAsyncResult *
......@@ -458,6 +471,9 @@ g_simple_async_result_async_result_iface_init (GAsyncResultIface *iface)
*
* Sets whether to handle cancellation within the asynchronous operation.
*
* This function has nothing to do with
* g_simple_async_result_set_check_cancellable(). It only refers to the
* #GCancellable passed to g_simple_async_result_run_in_thread().
**/
void
g_simple_async_result_set_handle_cancellation (GSimpleAsyncResult *simple,
......@@ -490,6 +506,10 @@ g_simple_async_result_get_source_tag (GSimpleAsyncResult *simple)
* Propagates an error from within the simple asynchronous result to
* a given destination.
*
* If the #GCancellable given to a prior call to
* g_simple_async_result_set_check_cancellable() is cancelled then this
* function will return %TRUE with @dest set appropriately.
*
* Returns: %TRUE if the error was propagated to @dest. %FALSE otherwise.
**/
gboolean
......@@ -498,6 +518,9 @@ g_simple_async_result_propagate_error (GSimpleAsyncResult *simple,
{
g_return_val_if_fail (G_IS_SIMPLE_ASYNC_RESULT (simple), FALSE);
if (g_cancellable_set_error_if_cancelled (simple->check_cancellable, dest))
return TRUE;
if (simple->failed)
{
g_propagate_error (dest, simple->error);
......@@ -1034,3 +1057,38 @@ g_simple_async_report_take_gerror_in_idle (GObject *object,
g_simple_async_result_complete_in_idle (simple);
g_object_unref (simple);
}
/**
* g_simple_async_result_set_check_cancellable:
* @simple: a #GSimpleAsyncResult
* @check_cancellable: a #GCancellable to check, or %NULL to unset
*
* Sets a #GCancellable to check before dispatching results.
*
* This function has one very specific purpose: the provided cancellable
* is checked at the time of g_simple_async_result_propagate_error() If
* it is cancelled, these functions will return an "Operation was
* cancelled" error (%G_IO_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 g_simple_async_result_set_handle_cancellation() function.
*
* Since: 2.32
**/
void
g_simple_async_result_set_check_cancellable (GSimpleAsyncResult *simple,
GCancellable *check_cancellable)
{
g_return_if_fail (G_IS_SIMPLE_ASYNC_RESULT (simple));
g_return_if_fail (check_cancellable == NULL || G_IS_CANCELLABLE (check_cancellable));
g_clear_object (&simple->check_cancellable);
if (check_cancellable)
simple->check_cancellable = g_object_ref (check_cancellable);
}
......@@ -83,6 +83,8 @@ gboolean g_simple_async_result_get_op_res_gboolean (GSimpleAsyncResul
void g_simple_async_result_set_check_cancellable (GSimpleAsyncResult *simple,
GCancellable *check_cancellable);
gpointer g_simple_async_result_get_source_tag (GSimpleAsyncResult *simple);
void g_simple_async_result_set_handle_cancellation (GSimpleAsyncResult *simple,
gboolean handle_cancellation);
......
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