DelayQueue

$ cargo test -- --nocapture

Response Latency        Count   Percent
             100            7   0.70%
             200           81   8.10%
             300          115   11.50%
             400          201   20.10%
             500          316   31.60%
             600           99   9.90%
            1000          181   18.10%
test test::test ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 9.99s