001package io.prometheus.metrics.core.util;
002
003import java.util.concurrent.CountDownLatch;
004import java.util.concurrent.Executors;
005import java.util.concurrent.ScheduledExecutorService;
006import java.util.concurrent.ScheduledFuture;
007import java.util.concurrent.ThreadFactory;
008import java.util.concurrent.TimeUnit;
009
010/**
011 * Used for scheduling maintenance tasks like purging outdated Exemplars or resetting native
012 * histograms.
013 */
014public class Scheduler {
015
016  private static class DaemonThreadFactory implements ThreadFactory {
017    private static int threadNum;
018
019    private static synchronized int nextThreadNum() {
020      return threadNum++;
021    }
022
023    @Override
024    public Thread newThread(Runnable runnable) {
025      Thread thread = new Thread(runnable, "prometheus-metrics-scheduler-" + nextThreadNum());
026      thread.setDaemon(true);
027      return thread;
028    }
029  }
030
031  private static final ScheduledExecutorService executor =
032      Executors.newSingleThreadScheduledExecutor(new DaemonThreadFactory());
033
034  public static ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
035    return executor.schedule(command, delay, unit);
036  }
037
038  /** For unit test. Wait until the executor Thread is running. */
039  @SuppressWarnings("FutureReturnValueIgnored")
040  public static void awaitInitialization() throws InterruptedException {
041    CountDownLatch latch = new CountDownLatch(1);
042    Scheduler.schedule(latch::countDown, 0, TimeUnit.MILLISECONDS);
043    latch.await();
044  }
045}