[Wesnoth-dev] Network operations and threading

[David White]

One of the more nasty issues that I think we should resolve before 1.0 
is described in this bug report: 
https://savannah.nongnu.org/bugs/index.php?func=detailitem&item_id=12614

The basic problem is that when a network connection is attempted, 
Wesnoth makes some blocking network calls, and waits for them to 
complete. In the case of a problem, Wesnoth may remain blocking for a 
long period of time, which will appear to the user as Wesnoth simply 
freezing.

I think this is very poor behavior and needs to be rectified, but I 
don't know enough about threading to confidently say what the best 
solution is.

My thought is that we should create some kind of interface for an 
'asynchronous operation'. In pseudo-code, I mean something like this:

execute_asynchronous_operation(asynchronous_operation& op, waiter& 
waiter_obj)
{
   start thread which executes operation defined by 'op'
   while(waiter_obj is still willing to wait for the operation to 
complete) {
      wait for 'op' to finish for 50ms, and if it has, return
   }

   terminate the operation and return
}

'waiter_obj' would perform some kind of operation to see if it's willing 
to wait -- such as display a dialog box to the user.

I think this would work okay...the main question I have is of how to 
terminate the operation. I'm not sure if it's okay to generally go 
around killing threads when they are in a blocking call such as 
resolving a hostname, or sending data over the network. Does anyone 
know? Alternatively I guess we could leave the thread running and have 
it joined() on program exit, hoping that it is done whatever it was 
doing by then.

Any thoughts or comments from those who know more about this than me 
would be appreciated. :)

David