AsyncObserver

[aleks-f]

#4414

Summary:

• existing functionality is only broken in the (now deprecated) AbstractObserver::accepts()
  This was a "quick and dirty" external path to the goal of filtering notifications by name (in addition to type-filtering)
• optional _matcher is added to NObserver
  (defaults to null and does not break existing functionality)
• NotificationCenter::observersTonotify() filters out the non-interested observers
  • this is the only place where dynamic_cast performance hit is taken
  • unnecessary casting is avoided when matcher is present and does not match
  • since observers are filtered, only the ones with matching type are notified, so notify() can cast statically
• AsyncObserver is child of NObserver and runs its own thread to decouple Notification posting from handling
• addedAsyncNotificationCenter, a child class of the NotificationCenter; currently, there is a problem with default static version of this observer on windows:
  

  poco/Foundation/testsuite/src/NotificationCenterTest.cpp

  Lines 252 to 255 in 71560b0

  	// TODO: static object thread hangs without this on windows
  	// for explanation/solution, see
  	// https://stackoverflow.com/questions/10441048/exit-thread-upon-deleting-static-object-during-unload-dll-causes-deadlock
  	nc.stop();

[matejk]

Looks OK to me.