org.apache.giraph.utils.TaskIdsPermitsBarrier.java Source code

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Here is the source code for org.apache.giraph.utils.TaskIdsPermitsBarrier.java

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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.giraph.utils;

import org.apache.hadoop.util.Progressable;
import org.apache.log4j.Logger;

import com.google.common.collect.Sets;

import java.util.HashSet;
import java.util.Set;

/**
 * This barrier is used when we don't know how many events are we waiting on
 * from the start. Instead we have a set of task ids, and each of those will,
 * at some point of time, give the information about how many events from it
 * should we expect. Barrier will be waiting for all the tasks to notify it
 * about that number of events, and than it will also wait for all the events
 * to happen.
 *
 * requirePermits() corresponds to task notifying us how many events from it
 * to expect, and releasePermits() notifies us about events happening.
 *
 * This class is currently used during preparation of aggregators.
 *
 * User must follow this protocol for concurrent access:
 *
 * (1) an object instance is constructed
 * (2) arbitrarily many times
 *     (2a) concurrent calls to requirePermits(), releasePermits() and
 *          waitForRequiredPermits() are issued
 *     (2b) waitForRequiredPermits() returns
 *
 * Note that the next cycle of calls to requirePermits() or releasePermits()
 * cannot start until the previous call to waitForRequiredPermits()
 * has returned.
 *
 * Methods of this class are thread-safe.
 */
public class TaskIdsPermitsBarrier {
    /** Class logger */
    private static final Logger LOG = Logger.getLogger(TaskIdsPermitsBarrier.class);
    /** Msecs to refresh the progress meter */
    private static final int MSEC_PERIOD = 10000;
    /** Maximum number of task ids to list in the log */
    private static final int MAX_TASK_IDS_TO_LOG = 10;
    /** Progressable for reporting progress */
    private final Progressable progressable;
    /** Number of permits we are currently waiting for */
    private long waitingOnPermits = 0;
    /** Set of task ids which required permits already */
    private final Set<Integer> arrivedTaskIds = new HashSet<Integer>();
    /** Logger */
    private final TimedLogger logger;

    /**
     * Constructor
     *
     * @param progressable Progressable for reporting progress
     */
    public TaskIdsPermitsBarrier(Progressable progressable) {
        this.progressable = progressable;
        logger = new TimedLogger(MSEC_PERIOD, LOG);
    }

    /**
     * Wait until permits have been required desired number of times,
     * and all required permits are available
     *
     * @param expectedTaskIds List of task ids which we are waiting permits from
     */
    public synchronized void waitForRequiredPermits(Set<Integer> expectedTaskIds) {
        while (arrivedTaskIds.size() < expectedTaskIds.size() || waitingOnPermits > 0) {
            try {
                wait(MSEC_PERIOD);
            } catch (InterruptedException e) {
                throw new IllegalStateException("waitForRequiredPermits: " + "InterruptedException occurred");
            }
            progressable.progress();
            if (LOG.isInfoEnabled()) {
                if (arrivedTaskIds.size() < expectedTaskIds.size()) {
                    String logSuffix = "";
                    if (expectedTaskIds.size() - arrivedTaskIds.size() <= MAX_TASK_IDS_TO_LOG) {
                        Sets.SetView<Integer> difference = Sets.difference(expectedTaskIds, arrivedTaskIds);
                        logSuffix = ", task ids: " + difference;
                    }
                    logger.info("waitForRequiredPermits: " + "Waiting for "
                            + (expectedTaskIds.size() - arrivedTaskIds.size())
                            + " more tasks to send their aggregator data" + logSuffix);
                } else {
                    logger.info("waitForRequiredPermits: " + "Waiting for " + waitingOnPermits
                            + " more aggregator requests");
                }
            }
        }

        // Reset for the next time to use
        arrivedTaskIds.clear();
        waitingOnPermits = 0;
    }

    /**
     * Require more permits. This will increase the number of times permits
     * were required. Doesn't wait for permits to become available.
     *
     * @param permits Number of permits to require
     * @param taskId Task id which required permits
     */
    public synchronized void requirePermits(long permits, int taskId) {
        arrivedTaskIds.add(taskId);
        waitingOnPermits += permits;
        notifyAll();
    }

    /**
     * Release one permit.
     */
    public synchronized void releaseOnePermit() {
        releasePermits(1);
    }

    /**
     * Release some permits.
     *
     * @param permits Number of permits to release
     */
    public synchronized void releasePermits(long permits) {
        waitingOnPermits -= permits;
        notifyAll();
    }
}