workers (a list) replace by queue when strategy equal fifo

[ghost]

Change workers when strategy equal fifo for performance

[getong]

It seems that the pr #111 is almost the same with this one, you can check it. If they are the same, this one can be closed.

[ghost]

It isn't the same with #111 . Here use queue while strategy equal fifo only, otherwise use list. And it use queue all the strategy in #111 . But you like.