com.spotify.helios.master.reaper.RateLimitedService.java Source code

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Here is the source code for com.spotify.helios.master.reaper.RateLimitedService.java

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/*
 * Copyright (c) 2016 Spotify AB.
 *
 * Licensed 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 com.spotify.helios.master.reaper;

import com.spotify.helios.agent.InterruptingScheduledService;

import com.google.common.util.concurrent.RateLimiter;

import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

/**
 * An abstract {@link InterruptingScheduledService} that is rate limited between defined
 * units of work within {@link #runOneIteration()}. Use this class if you need to retrieve a
 * complete set of items to process and then pause between operating on each item.
 *
 * A use case is when you need to get a list of nodes from ZooKeeper and for each node run three
 * more ZooKeeper operations. You need to get all the nodes in a single {@link #runOneIteration()},
 * but you want to pause between processing each node because the fan-out of ZooKeeper operations
 * will hammer it.
 */
abstract class RateLimitedService<T> extends InterruptingScheduledService {

    private final long initialDelay;
    private final long delay;
    private final TimeUnit timeUnit;
    private final RateLimiter rateLimiter;

    RateLimitedService(final double permitsPerSecond, final long initialDelay, final long delay,
            final TimeUnit timeUnit) {
        this.rateLimiter = RateLimiter.create(permitsPerSecond);
        this.initialDelay = initialDelay;
        this.delay = delay;
        this.timeUnit = timeUnit;
    }

    /**
     * Collect items to process.
     * @return An iterable of T.
     */
    abstract Iterable<T> collectItems();

    /**
     * Process the item.
     * @param item An instance of T.
     */
    abstract void processItem(final T item);

    @Override
    protected void runOneIteration() {
        for (final T item : collectItems()) {
            rateLimiter.acquire();
            processItem(item);
        }
    }

    @Override
    protected ScheduledFuture<?> schedule(final Runnable runnable, final ScheduledExecutorService executorService) {
        return executorService.scheduleWithFixedDelay(runnable, initialDelay, delay, timeUnit);
    }
}