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A fork of the Apache Cassandra Project that uses Lucene indexes for providing near real time search such as ElasticSearch or Solr, including full text search capabilities, multi-dimensional queries, and relevance scoring.
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/*
* 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.scheduler;
import java.util.Map;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeoutException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.config.RequestSchedulerOptions;
import org.cliffc.high_scale_lib.NonBlockingHashMap;
/**
* A very basic Round Robin implementation of the RequestScheduler. It handles
* request groups identified on user/keyspace by placing them in separate
* queues and servicing a request from each queue in a RoundRobin fashion.
* It optionally adds weights for each round.
*/
public class RoundRobinScheduler implements IRequestScheduler
{
private static final Logger logger = LoggerFactory.getLogger(RoundRobinScheduler.class);
//Map of queue id to weighted queue
private final NonBlockingHashMap queues;
private final Semaphore taskCount;
// Tracks the count of threads available in all queues
// Used by the the scheduler thread so we don't need to busy-wait until there is a request to process
private final Semaphore queueSize = new Semaphore(0, false);
private final int defaultWeight;
private final Map weights;
public RoundRobinScheduler(RequestSchedulerOptions options)
{
defaultWeight = options.default_weight;
weights = options.weights;
// the task count is acquired for the first time _after_ releasing a thread, so we pre-decrement
taskCount = new Semaphore(options.throttle_limit - 1);
queues = new NonBlockingHashMap();
Runnable runnable = new Runnable()
{
public void run()
{
while (true)
{
schedule();
}
}
};
Thread scheduler = new Thread(runnable, "REQUEST-SCHEDULER");
scheduler.start();
logger.info("Started the RoundRobin Request Scheduler");
}
public void queue(Thread t, String id, long timeoutMS) throws TimeoutException
{
WeightedQueue weightedQueue = getWeightedQueue(id);
try
{
queueSize.release();
try
{
weightedQueue.put(t, timeoutMS);
// the scheduler will release us when a slot is available
}
catch (TimeoutException e)
{
queueSize.acquireUninterruptibly();
throw e;
}
catch (InterruptedException e)
{
queueSize.acquireUninterruptibly();
throw e;
}
}
catch (InterruptedException e)
{
throw new RuntimeException("Interrupted while queueing requests", e);
}
}
public void release()
{
taskCount.release();
}
private void schedule()
{
queueSize.acquireUninterruptibly();
for (Map.Entry request : queues.entrySet())
{
WeightedQueue queue = request.getValue();
//Using the weight, process that many requests at a time (for that scheduler id)
for (int i=0; i