Queue
Hazelcast distributed queue is an implementation of java.util.concurrent.BlockingQueue.
import com.hazelcast.core.Hazelcast;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
import com.hazelcast.config.Config;
Config cfg = new Config();
HazelcastInstance hz = Hazelcast.newHazelcastInstance(cfg);
BlockingQueue<MyTask> q = hz.getQueue("tasks");
q.put(new MyTask());
MyTask task = q.take();
boolean offered = q.offer(new MyTask(), 10, TimeUnit.SECONDS);
task = q.poll (5, TimeUnit.SECONDS);
if (task != null) {
//process task
}
FIFO ordering will apply to all queue operations cluster wide. User objects (such as MyTask in the example above), that are (en/de)queued have to be Serializable. By configuring max-size for queue, one can obtain a bounded queue.
A sample configuration is shown below.
<hazelcast>
...
<queue name="tasks">
<!--
Maximum size of the queue. When queue size reaches the maximum,
all put operations will get blocked until the queue size
goes down below the maximum.
Any integer between 0 and Integer.MAX_VALUE. 0 means Integer.MAX_VALUE. Default is 0.
-->
<max-size>10000</max-size>
<!--
Number of backups. If 1 is set as the backup-count for example,
then all entries of the map will be copied to another JVM for
fail-safety. Valid numbers are 0 (no backup), 1, 2 ... 6.
Default is 1.
-->
<backup-count>1</backup-count>
<!--
Number of async backups. 0 means no backup.
-->
<async-backup-count>0</async-backup-count>
<!--
QueueStore implementation to persist items.
'binary' property indicates that storing items will be in binary format
'memory-limit' property enables 'overflow to store' after reaching limit
'bulk-load' property enables bulk-loading from store
-->
<queue-store>
<class-name>com.hazelcast.QueueStore</class-name>
<properties>
<property name="binary">false</property>
<property name="memory-limit">1000</property>
<property name="bulk-load">250</property>
</properties>
</queue-store>
</queue>
</hazelcast>