* class SafeQueue
* cleanup includes
* space
* add timeout
use try_poll
* add function empty() & size()
* class SafeQueue
* add timeout
use try_poll
* add function empty() & size()
* rebase master
* rebase master
* for loop
* fix bug
old-commit-hash: e6783f4d9f10a256a4c301eb1d1843d9e2a17ab6