Cancelling gupnp_service_info_get_introspection_async

[Mark Ryan <mark d ryan linux intel com>]

Hi All,

We've identified a problem with 
gupnp_service_info_get_introspection_async.  The problem is simple. 
There is no way to cancel a request to 
gupnp_service_info_get_introspection_async and this can make it 
difficult for GUPnP clients that call this function to shutdown cleanly.

Technically, it is easy to add a cancel function, but there are a number 
of possible solutions and some of them involve breaking the backwards 
compatibility, so I thought it would be better to raise the issue on the 
mailing list before preparing a patch.  For me there are two questions.

1. Do we modify gupnp_service_info_get_introspection_async directly or 
deprecate it and provide a new function that contains an extra parameter 
or return value used for cancellation?  I'm guessing we want to do the 
latter.  If we provide a new function, what should it be called?

2. How should the clients cancel 
gupnp_service_info_get_introspection_async?  Should they pass in a 
GCancellable object, which they can pass to a call to 
g_cancellable_cancel at a later stage, or should they call a new _cancel 
function to cancel the retrieval of introspection data.  The first 
option would be more consistent with modern GLib interfaces, but the 
second, would be more consistent with how the existing GUPnP 
asynchronous functions, such as gupnp_service_proxy_begin_action, 
currently work.

Any thoughts?

Mark