Re: Updated proposal for making the GtkFileChooser code asynchronous

[Soeren Sandmann <sandmann daimi au dk>]

Kristian Rietveld <kris imendio com> writes:

> 1. Let's start out with a somewhat more general change.  We need to be able
>    to cancel currently running asynchronous operations.  For this we need
>    to have a handle on an operation, so we need to introduce a
>    GtkFileSystemHandle.  The GtkFileSystemHandle will be a GObject:
> 
>    struct _GtkFileSystemHandle
>    {
>      GObject parent_instance;
> 
>      GtkFileSystem *file_system;
> 
>      guint cancelled : 1;		/* indicates whether the operation
> 					   has been cancelled or not */
>    };
> 
>    struct _GtkFileSystemHandleClass
>    {
>      GObjectClass parent_class;
>    };
> 
>    File system backends can of course subclass GtkFileSystemHandle and
>    add their own fields as required.  We will add a call which we can use to
>    actually cancel an operation:
> 
>    void gtk_file_system_cancel_operation (GtkFileSystemHandle
>    *handle);

If you cancel an operation such as create_folder() before the callback
is called, what are the semantics?

        1 the operation will not have been completed, ie., no folder
          was created and no folder will be created

        2 the operation may or may not be completed depending on where
          the thread happens to be when you cancel the operation

        3 the operation will be completed anyway

        4 something else

Number 1 seems impossible to implement with threads without getting
into hairy things like thread cancellation. Number 2 seems nasty, and
3 makes cancelling pretty useless.

Also, the callback is always called, even if you cancel the operation,
right?

>    The function gtk_file_system_get_info() itself does not take an
>    GError argument.  All errors will be reported via the callback, this means
>    that error handling will only have to be implemented at a single place.
>    The error argument of the callback will be NULL when no error
>    occurred.

Shouldn't error be const, or are you expected to free it (if so, why?)?


Soren