[xmonad] Patch: changes in Prompt and new module

[wagnerdm at seas.upenn.edu]

Quoting Brandon Allbery <allbery.b at gmail.com>:

> On Fri, Jun 29, 2012 at 3:16 PM, <wagnerdm at seas.upenn.edu> wrote:
>
> Built with -threaded, a forkOS thread could do dbus calls and then
> establish its own Xlib connection and XSendEvent() or install a property on
> the root window to relay the result.  This doesn't necessarily need to be a
> one-way connection, but nothing in the main thread can block to wait on a
> response from the dbus thread (instead, use handleEventHook).

My understanding is that if xmonad were built with -threaded, forkIO  
would be enough (forkOS would not be necessary). Safe foreign imports  
are run on their own (OS) thread by the threaded runtime anyway. For  
the same reason, I don't really think it's necessary to get at X's fd  
and tell the IO manager about it. (If there are blocking X calls that  
are imported unsafe, I consider that a bug, and would happily make a  
release of the X11 package fixing it.) The only annoyance left would  
be, as you say, communicating with the main thread -- which would have  
to roundtrip through X. Only an architectural change to xmonad can fix  
that.

However, I wouldn't be surprised if there were other gotchas related  
to turning on -threaded. I vaguely recall that this was attempted in  
the past and had some issues. Perhaps it had something to do with  
asynchronous exceptions and xmonad's masking stuff...?

~d