时间轮算法

1. Hashed and Hierarchical Timing Wheels A paper by George Varghese and Tony Lauck

4. Currently Used Timer Schemes a b c d e Can maintain absolute expiry time or the timer interval START_TIMER = O(1) STOP_TIMER = O(1) PER_TICK_BOOKKEEPING = O(n) a b c d e f maintain absolute expiry time START_TIMER = O(n) STOP_TIMER = O(1) PER_TICK_BOOKKEEPING = O(1)

5. Tree based timers a b c d a b c d maintain absolute expiry time START_TIMER = O(log(n)) STOP_TIMER = O(1) PER_TICK_BOOKKEEPING = O(1) Can degenerate to a linear list in case of equal Interval timers START_TIMER = O(n) STOP_TIMER = O(1) PER_TICK_BOOKKEEPING = O(1)

9. Hierarchical Timing Wheel 1 2 3 4 5 6 7 0 3 5 7 5 2 1 1 Hours wheel 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 Minutes wheel Seconds wheel 1 3 3 5 3 7 1 5

11. Comparison START_TIMER STOP_TIMER PER_TICK O(1) Straight Fwd O(1) O(n) Sequential List O(n) O(1) O(1) Tree Based O(log(n)) O(1) O(1) Simple Wheel O(1) O(1) O(1) High memory requirement Hashed Wheel (sorted) Hashed Wheel (unsorted) Hierarchical Wheels O(n) worst case O(1) avg O(1) O(m) O(1) O(1) O(1) O(1) O(n) worst case O(1) avg O(1)