Adds an idle event as with g_idle_add, but using the given async_context.
If you want function to run "right away", use add_completion, since
that sets a higher priority on the SocketSource than add_idle does.
| async_context |
the MainContext to dispatch the I/O watch in, or |
| function |
the callback to invoke at idle time |
| data |
user data to pass to |
|
a SocketSource, which can be removed from |