Github user joshelser commented on a diff in the pull request:
https://github.com/apache/accumulo/pull/223#discussion_r103740091
--- Diff:
server/monitor/src/main/java/org/apache/accumulo/monitor/util/AccumuloMonitorAppender.java
---
@@ -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
+ *
+ * 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.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;
+import org.apache.log4j.net.SocketAppender;
+import org.apache.zookeeper.data.Stat;
+
+import com.google.common.net.HostAndPort;
+
+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;
+ });
+ }
+
+ @Override
+ public void activateOptions() {
+ // only schedule it once (in case options get activated more than
once); not sure if this is possible
+ if (trackerScheduled.compareAndSet(false, true)) {
+ // wait 5 seconds, then run every 5 seconds
+ executorService.scheduleAtFixedRate(new MonitorTracker(), 5, 5,
TimeUnit.SECONDS);
+ }
+ super.activateOptions();
+ }
+
+ @Override
+ public void close() {
+ if (!executorService.isShutdown()) {
+ executorService.shutdownNow();
+ }
+ super.close();
+ }
+
+ private class MonitorTracker implements Runnable {
+
+ private String path;
+ private ZooCache zooCache;
+
+ private long lastModifiedTransactionId;
+ private SocketAppender lastSocketAppender;
+
+ public MonitorTracker() {
+
+ // path and zooCache are lazily set the first time this tracker is
run
+ // this allows the tracker to be constructed and scheduled during
log4j initialization without
+ // triggering any actual logs from the Accumulo or ZooKeeper code
+ this.path = null;
+ this.zooCache = null;
+
+ this.lastModifiedTransactionId = 0;
+ this.lastSocketAppender = null;
+ }
+
+ @Override
+ public void run() {
--- End diff --
I was thinking some unit tests for these methods would be good, not
necessarily high-level integration. Just some sanity checks that exercise your
code given the state coming out of ZK.
I'm sure there will be something wrong with what you have (seems to be the
constant when working with ZK). Having some sort of boilerplate in place to
test "given state X, observe change y, z should happen" would help better fix
the inevitable issue.
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