[PEAK] Simplifying configuration for PEAK+Twisted apps

[Phillip J. Eby]

After thinking over the issues brought up by Bob Ippolito, and their 
consequences for configuring a Twisted reactor for use with PEAK, I think 
I'd like to propose to do the following:

* Define a property name whose truth is used to signal the "twistedness" of 
a service area

* Add 'running.ifTwisted(ob,twistedValue,untwistedValue)', that returns 
'twistedValue' if the service area containing 'ob' is configured to be used 
with Twisted, or 'untwistedValue' otherwise.

* Add 'running.makeTwisted(ob)', which tries to configure the service area 
containing 'ob' to be used with Twisted, or raises an error if the service 
area has already been used in an "untwisted" fashion.

* Configure all of the appropriate event-management component factories 
(running.IMainLoop, events.IScheduler, events.ISelector, and 
running.IBasicReactor) to use 'ifTwisted()' to select an appropriate 
implementation.

* Configure the running.ITwistedReactor component factory to invoke 
'makeTwisted()' on the applicable service area before returning the 
twisted.internet.reactor.  This will have the unfortunate side effect of 
having any lookups for 'config.FactoryFor(running.ITwistedReactor)' to 
attempt forcing a Twisted configuration, but in practice I think the 
sensible answer to this issue would be "don't do that."

With these changes, I think we could get rid of the current 
'getTwisted()'/etc. kludges, and also avoid having to have a bunch of 
manual component factory configuration operations in order to use a Twisted 
reactor with PEAK.  The net result is that no changes to current 
PEAK+Twisted apps would be required, as long as you adhere to the current 
constraint of looking up ITwistedReactor before any attempt is made to use 
an IBasicReactor.  IBasicReactor would still be phased out in a4, though, 
since 'peak.events' will provide a superior alternative by then.

For apps that use Twisted with options like a GUI, "real" threads, etc., I 
think there should probably be some way to get those options installed by 
the ITwistedReactor factory.  But I'm not familiar enough with the use 
cases for those to be comfortable specifying a mechanism.  Maybe it'd 
suffice to do something like:

[peak.running]
twistedness = importString('twisted.internet.somereactor').install() or True

if you wanted to use a special Twisted reactor.