org.cache2k.expiry.Expiry Maven / Gradle / Ivy
package org.cache2k.expiry;
/*
* #%L
* cache2k API
* %%
* Copyright (C) 2000 - 2020 headissue GmbH, Munich
* %%
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
* #L%
*/
/**
* Utility methods and constants to use inside expire policy and friends.
*
* @author Jens Wilke
* @see ExpiryPolicy
* @see org.cache2k.integration.ResiliencePolicy
* @see org.cache2k.Cache#expireAt
*/
public class Expiry implements ExpiryTimeValues {
/**
* Convert the time value to a time representing an a sharp expiry.
* This essentially negates the time value and is provided for a more speaking coding style.
*
* @param millis expiry time since the milliseconds since epoch or {@link #ETERNAL} if no
* expiry is requested.
* @throws IllegalArgumentException if the time value is negative
*/
public static long toSharpTime(long millis) {
if (millis == ETERNAL) {
return ETERNAL;
}
if (millis < 0) {
return millis;
}
return -millis;
}
/**
* Helper to calculate the next expiry out of two expiry times that
* may be up next. Return the time value that is closest or equal to
* the current time. Time values in the past are ignored. If all times
* are in the past, returns {@link #ETERNAL}.
*
* @param loadTime the current time in millis since epoch
* @param candidate1 candidate time for next expiry
* @param candidate2 candidate time for next expiry
* @return either first or second candidate or {@link #ETERNAL}
*/
public static long earliestTime(long loadTime, long candidate1, long candidate2) {
if (candidate1 >= loadTime) {
if (candidate1 < candidate2 || candidate2 < loadTime) {
return candidate1;
}
}
if (candidate2 >= loadTime) {
return candidate2;
}
return ETERNAL;
}
/**
* Combine a refresh time span and an expiry at a specified point in time.
*
* If the expiry time is far ahead of time the refresh time span takes
* precedence. If the point in time is close by this time takes precedence.
* If the refresh time is too close to the requested point an earlier refresh
* time is used to keep maximum distance to the requested point time, which is
* {@code abs(pointInTime) - refreshAfter}
*
*
Rationale: Usually the expiry is allowed to lag behind. This is okay
* when a normal expiry interval is used. If sharp expiry is requested an
* old value may not be visible at or after the expiry time. Refresh ahead
* implies lagging expiry, since the refresh is triggered when the value would
* usually expire. The two concepts can be combined in the expiry policy, e.g.
* using an interval for triggering refresh ahead and requesting a sharp expiry
* only when needed. If effective expiry time for the lagging variant and the
* for the sharp variant are in close proximity, conflicts need to be resolved.
*
* @param loadTime time when the load was started
* @param refreshAfter time span in milliseconds when the next refresh should happen
* @param pointInTime time in milliseconds since epoch for the next expiry. Can be negative
* if sharp expiry is requested, or {@link #ETERNAL} if no point in time
* expiry is needed.
*/
public static long mixTimeSpanAndPointInTime(long loadTime, long refreshAfter, long pointInTime) {
long refreshTime = loadTime + refreshAfter;
if (refreshTime < 0) {
refreshTime = ETERNAL;
}
if (pointInTime == ETERNAL) {
return refreshTime;
}
if (pointInTime > refreshTime) {
return refreshTime;
}
long absPointInTime = Math.abs(pointInTime);
if (absPointInTime <= refreshTime) {
return pointInTime;
}
long pointInTimeMinusDelta = absPointInTime - refreshAfter;
if (pointInTimeMinusDelta < refreshTime) {
return pointInTimeMinusDelta;
}
return refreshTime;
}
}