[GitHub] [druid] clintropolis commented on a change in pull request #10732: Add a config for monitorScheduler type

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clintropolis commented on a change in pull request #10732:
URL: https://github.com/apache/druid/pull/10732#discussion_r555503062



##########
File path: core/src/main/java/org/apache/druid/java/util/metrics/ClockDriftSafeMonitorScheduler.java
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@@ -0,0 +1,134 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+package org.apache.druid.java.util.metrics;
+
+import io.timeandspace.cronscheduler.CronScheduler;
+import io.timeandspace.cronscheduler.CronTask;
+import org.apache.druid.java.util.common.logger.Logger;
+import org.apache.druid.java.util.emitter.service.ServiceEmitter;
+
+import java.util.List;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+
+/**
+ * A {@link MonitorScheduler} implementation based on {@link CronScheduler}.
+ */
+public class ClockDriftSafeMonitorScheduler extends MonitorScheduler
+{
+  private static final Logger LOG = new Logger(ClockDriftSafeMonitorScheduler.class);
+
+  private final CronScheduler monitorScheduler;
+  private final ExecutorService monitorRunner;
+
+  public ClockDriftSafeMonitorScheduler(
+      MonitorSchedulerConfig config,
+      ServiceEmitter emitter,
+      List<Monitor> monitors,
+      CronScheduler monitorScheduler,
+      ExecutorService monitorRunner
+  )
+  {
+    super(config, emitter, monitors);
+    this.monitorScheduler = monitorScheduler;
+    this.monitorRunner = monitorRunner;
+  }
+
+  @Override
+  void startMonitor(final Monitor monitor)
+  {
+    monitor.start();
+    long rate = getConfig().getEmitterPeriod().getMillis();
+    final AtomicReference<Future<?>> scheduleFutureReference = new AtomicReference<>();
+    Future<?> scheduledFuture = monitorScheduler.scheduleAtFixedRate(
+        rate,
+        rate,
+        TimeUnit.MILLISECONDS,
+        new CronTask()
+        {
+          private Future<?> scheduleFuture = null;

Review comment:
       nit: I wonder if these can have better names: `scheduledFuture`, `scheduleFuture`, and `scheduleFutureReference` is a bit too close to each other and is sort of confusing at first glance. Should the inner one perhaps be called `cancellationFuture` or something to distinguish it from the external one?




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