[COLLECTIONS-469] PassiveExpiringMap performance improvement and refreshing policy

• Type: New Feature
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Fix Version/s: 4.x
• Component/s: Map
• Assignee: Unassigned
• Reporter: l0co
• Created: 14/May/13 11:05
• Updated: 24/Jun/13 19:34

Description

A copy from COLLECTIONS-467.

Two remarks about current trunk implementation of PassiveExpiringMap.

You should additionally keep the value of the next element timeout (the youngest timeout) in object field, so that you don't need to iterate through whole map to find elements for expiration on each call. It improves performance by calculating only simple if for most cases:

public class PassiveExpiringMap {
  long youngestTimeoutMs = 0; // assert to have next timeout time for youngest element here always, or 0 if map is empty
  
  private void removeAllExpired(final long now) {
    if (youngestTimeoutMs>0 && youngestTimeoutMs<=now) {
      // do the cleanup
    }
  }
}

The second remark concerns the refreshing policy. As I can see there's no refreshing policy in current implementation, there should be at last two policies: NoRefresh (working as the current) and RefreshOnHit - which updates element expiration time when the element is "hit" (eg. by get()), so that the map always removes the least used resources.