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DelayQueueDemo.java
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// threads/DelayQueueDemo.java
// (c)2016 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://mindviewinc.com/Books/OnJava/ for more book information.
import java.util.concurrent.*;
import java.util.*;
import static java.util.concurrent.TimeUnit.*;
class DelayedTask implements Runnable, Delayed {
private static int counter = 0;
private final int id = counter++;
private final int delta;
private final long trigger;
protected static List<DelayedTask> sequence =
new ArrayList<>();
public DelayedTask(int delayInMilliseconds) {
delta = delayInMilliseconds;
trigger = System.nanoTime() +
NANOSECONDS.convert(delta, MILLISECONDS);
sequence.add(this);
}
@Override
public long getDelay(TimeUnit unit) {
return unit.convert(
trigger - System.nanoTime(), NANOSECONDS);
}
@Override
public int compareTo(Delayed arg) {
DelayedTask that = (DelayedTask)arg;
if(trigger < that.trigger) return -1;
if(trigger > that.trigger) return 1;
return 0;
}
@Override
public void run() { System.out.print(this + " "); }
@Override
public String toString() {
return String.format("[%1$-4d]", delta) +
" Task " + id;
}
public String summary() {
return "(" + id + ":" + delta + ")";
}
public static class EndSentinel extends DelayedTask {
private ExecutorService exec;
public EndSentinel(int delay, ExecutorService e) {
super(delay);
exec = e;
}
@Override
public void run() {
for(DelayedTask pt : sequence) {
System.out.print(pt.summary() + " ");
}
System.out.println();
System.out.println(this + " Calling shutdownNow()");
exec.shutdownNow();
}
}
}
class DelayedTaskConsumer implements Runnable {
private DelayQueue<DelayedTask> q;
public DelayedTaskConsumer(DelayQueue<DelayedTask> q) {
this.q = q;
}
@Override
public void run() {
try {
while(!Thread.interrupted())
q.take().run(); // Run task with current thread
} catch(InterruptedException e) {
// Acceptable way to exit
}
System.out.println("Finished DelayedTaskConsumer");
}
}
public class DelayQueueDemo {
public static void main(String[] args) {
SplittableRandom rand = new SplittableRandom(47);
ExecutorService es = Executors.newCachedThreadPool();
DelayQueue<DelayedTask> queue =
new DelayQueue<>();
// Fill with tasks that have random delays:
for(int i = 0; i < 20; i++)
queue.put(new DelayedTask(rand.nextInt(5000)));
// Set the stopping point
queue.add(new DelayedTask.EndSentinel(5000, es));
es.execute(new DelayedTaskConsumer(queue));
}
}
/* Output:
[70 ] Task 10 [125 ] Task 13 [267 ] Task 19 [635 ] Task 0
[650 ] Task 16 [682 ] Task 17 [807 ] Task 11 [1131] Task 18
[1177] Task 4 [1193] Task 9 [1634] Task 15 [1656] Task 6
[2400] Task 12 [3479] Task 5 [3737] Task 1 [3768] Task 7
[3941] Task 2 [4720] Task 3 [4762] Task 14 [4948] Task 8
(0:635) (1:3737) (2:3941) (3:4720) (4:1177) (5:3479)
(6:1656) (7:3768) (8:4948) (9:1193) (10:70) (11:807)
(12:2400) (13:125) (14:4762) (15:1634) (16:650) (17:682)
(18:1131) (19:267) (20:5000)
[5000] Task 20 Calling shutdownNow()
Finished DelayedTaskConsumer
*/