The current implementation uses busy-wait and checking flags to
communicate between threads. It wastes a lot of CPU powers. With
python 2.6 is required for Swift, the communication between
threads should now be using queue and signal mechanisms. This
patch removed the busy-wait loops and use queue and queue join
for threads coordination which will not consume CPU cycles if
a thread is blocked.
Change-Id: I648cd637a92a159d5c13baa83f357cee2dfe7937
874e0e4427