Will close() signal all the threads that have called WaitOne()?
close()
threads
WaitOne()
If not, what's the best way to do this?
It will cause an AbandonedMutexException. The correct way of using this class is not to call close while waiters are active.
AbandonedMutexException
See http://msdn.microsoft.com/en-us/library/58195swd.aspx