glib:source-add-child-source (source child)

source -- a g:source instance
child -- a second g:source instance that source should "poll"

Adds child to source as a "polled" source. When source is added to a g:main-context instance, child will be automatically added with the same priority, when child is triggered, it will cause source to dispatch (in addition to calling its own callback), and when source is destroyed, it will destroy child as well. The source instance will also still be dispatched if its own prepare/check functions indicate that it is ready.

The source instance will hold a reference on child while child is attached to it.