10.4.5. ExpirationAlgorithm
org.jboss.cache.eviction.ExpirationAlgorithm is a policy that evicts nodes based on an absolute expiration time. The expiration time is indicated using the org.jboss.cache.Node.put() method, using a String key expiration and the absolute time as a java.lang.Long object, with a value indicated as milliseconds past midnight January 1st, 1970 UTC (the same relative time as provided by java.lang.System.currentTimeMillis() ).
This policy guarantees a constant order (
O (1) ) for adds and removals. Internally, a sorted set (TreeSet) containing the expiration time and Fqn of the nodes is stored, which essentially functions as a heap.
This policy has the following configuration parameters:
expirationKeyName- This is the Node key name used in the eviction algorithm. The configuration default isexpiration.maxNodes- This is the maximum number of nodes allowed in this region. 0 denotes immediate expiry, -1 denotes no limit.
The following listing shows how the expiration date is indicated and how the policy is applied:
Cache cache = DefaultCacheFactory.createCache();
Fqn fqn1 = Fqn.fromString("/node/1");
Long future = new Long(System.currentTimeMillis() + 2000);
// sets the expiry time for a node
cache.getRoot().addChild(fqn1).put(ExpirationConfiguration.EXPIRATION_KEY, future);
assertTrue(cache.getRoot().hasChild(fqn1));
Thread.sleep(5000);
// after 5 seconds, expiration completes
assertFalse(cache.getRoot().hasChild(fqn1));
Note that the expiration time of nodes is only checked when the region manager wakes up every
wakeUpIntervalSeconds , so eviction may happen a few seconds later than indicated.
