Summary

NotificationCenter methods call observer methods (start(), disable()) while holding the internal mutex, creating a lock-order-inversion with Observer's mutex.

Deadlock Scenario

Thread A (eg. SocketRreactor::run()):

1. Observer::notify() holds Observer mutex (M0)
2. Handler calls removeEventHandler() (documented as safe)
3. → hasObserver() waits for NotificationCenter mutex (M1)

Thread B (shutdown):

1. removeObserver() holds NotificationCenter mutex (M1)
2. → disable() waits for Observer mutex (M0)

Result: Deadlock (M0 → M1, M1 → M0)

Affected Methods

• addObserver() - calls start() under lock
• removeObserver() - calls disable() under lock
• clear() - calls disable() under lock

Fix

Release lock before calling observer methods:

void NotificationCenter::addObserver(const AbstractObserver& observer)
{
	AbstractObserverPtr pObserver = observer.clone();
	{
		RWLock::ScopedWriteLock lock(_mutex);
		_observers.push_back(pObserver);
	}
	// Start outside the lock to avoid deadlock with Observer mutex
	pObserver->start();
}