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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
* 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.cassandra.utils;
import java.io.File;
import java.util.concurrent.TimeUnit;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.concurrent.ScheduledExecutors;
public class ResourceWatcher
{
public static void watch(String resource, Runnable callback, int period)
{
ScheduledExecutors.scheduledTasks.scheduleWithFixedDelay(new WatchedResource(resource, callback), period, period, TimeUnit.MILLISECONDS);
}
public static class WatchedResource implements Runnable
{
private static final Logger logger = LoggerFactory.getLogger(WatchedResource.class);
private final String resource;
private final Runnable callback;
private long lastLoaded;
public WatchedResource(String resource, Runnable callback)
{
this.resource = resource;
this.callback = callback;
lastLoaded = 0;
}
public void run()
{
try
{
String filename = FBUtilities.resourceToFile(resource);
long lastModified = new File(filename).lastModified();
if (lastModified > lastLoaded)
{
callback.run();
lastLoaded = lastModified;
}
}
catch (Throwable t)
{
JVMStabilityInspector.inspectThrowable(t);
logger.error(String.format("Timed run of %s failed.", callback.getClass()), t);
}
}
}
}