/* * 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<String, WeightedQueue> 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<String, Integer> 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<String, WeightedQueue>(); 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 | 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<String,WeightedQueue> 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<queue.weight; i++) { Thread t = queue.poll(); if (t == null) break; else { taskCount.acquireUninterruptibly(); queueSize.acquireUninterruptibly(); } } } queueSize.release(); } /* * Get the Queue for the respective id, if one is not available * create a new queue for that corresponding id and return it */ private WeightedQueue getWeightedQueue(String id) { WeightedQueue weightedQueue = queues.get(id); if (weightedQueue != null) // queue existed return weightedQueue; WeightedQueue maybenew = new WeightedQueue(id, getWeight(id)); weightedQueue = queues.putIfAbsent(id, maybenew); if (weightedQueue == null) { return maybenew; } // another thread created the queue return weightedQueue; } Semaphore getTaskCount() { return taskCount; } private int getWeight(String weightingVar) { return (weights != null && weights.containsKey(weightingVar)) ? weights.get(weightingVar) : defaultWeight; } }