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From ctubbsii <>
Subject [GitHub] accumulo pull request #223: ACCUMULO-4409 Create AccumuloMonitorAppender
Date Wed, 01 Mar 2017 17:31:31 GMT
Github user ctubbsii commented on a diff in the pull request:
    --- Diff: server/monitor/src/main/java/org/apache/accumulo/monitor/util/
    @@ -0,0 +1,153 @@
    + * 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
    + *
    + *
    + *
    + * 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.accumulo.monitor.util;
    +import static java.nio.charset.StandardCharsets.UTF_8;
    +import java.util.concurrent.Executors;
    +import java.util.concurrent.ScheduledExecutorService;
    +import java.util.concurrent.TimeUnit;
    +import java.util.concurrent.atomic.AtomicBoolean;
    +import org.apache.accumulo.core.Constants;
    +import org.apache.accumulo.core.client.Instance;
    +import org.apache.accumulo.core.conf.Property;
    +import org.apache.accumulo.core.zookeeper.ZooUtil;
    +import org.apache.accumulo.fate.zookeeper.ZooCache;
    +import org.apache.accumulo.fate.zookeeper.ZooCacheFactory;
    +import org.apache.accumulo.server.client.HdfsZooInstance;
    +import org.apache.log4j.AsyncAppender;
    +public class AccumuloMonitorAppender extends AsyncAppender {
    +  private final ScheduledExecutorService executorService;
    +  private final AtomicBoolean trackerScheduled;
    +  /**
    +   * A Log4j Appender which follows the registered location of the active Accumulo monitor
service, and forwards log messages to it
    +   */
    +  public AccumuloMonitorAppender() {
    +    // create the background thread to watch for updates to monitor location
    +    trackerScheduled = new AtomicBoolean(false);
    +    executorService = Executors.newSingleThreadScheduledExecutor(runnable -> {
    +      Thread t = new Thread(runnable, AccumuloMonitorAppender.class.getSimpleName() +
" Location Tracker");
    +      t.setDaemon(true);
    +      return t;
    --- End diff --
    Maybe. I just don't see much difference from remembering to do `new Daemon` instead of
`new Thread` and remembering to do `setDaemon(true)`. The former adds a level of obfuscation
that a developer has to track, but otherwise, they seem to be equivalent to me from the perspective
of what the developer is responsible for remembering to do. The only way the `Daemon` class
is better is if we had an executor service whose API explicitly wanted those instead of `Thread`.
It's not the case here, but maybe it's the case elsewhere in Accumulo. I haven't looked.

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