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Concourse is a self-tuning database that is designed for both ad hoc analytics and high volume transactions at scale. Developers use Concourse to quickly build mission critical software while also benefiting from real time insight into their most important data. With Concourse, end-to-end data management requires no extra infrastructure, no prior configuration and no additional coding–all of which greatly reduce costs and allow developers to focus on core business problems.

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/*
 * Copyright (c) 2013-2019 Cinchapi Inc.
 *
 * 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.cinchapi.concourse.util;

import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Queue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;

import com.cinchapi.common.base.CheckedExceptions;
import com.google.common.base.Preconditions;

/**
 * Static factory methods for returning objects that implement the {@link Queue}
 * interface.
 * 
 * @author Jeff Nelson
 */
public final class Queues {

    /**
     * Return a simple {@link Queue} that can be used in a single thread.
     * 
     * @return the {@link Queue}
     */
    public static  Queue newSingleThreadedQueue() {
        return new ArrayDeque();
    }

    /**
     * Perform the {@link BlockingQueue#drainTo(Collection)} operation, but
     * block indefinitely until at least one element is available.
     * 
     * @param queue the {@link BlockingQueue} in which to perform the
     *            {@link BlockingQueue#drainTo(Collection) drainTo} method
     * @param buffer the collection into which the elements are drained
     * @return the number of elements that are drained
     * @throws InterruptedException
     */
    public static  int blockingDrain(BlockingQueue queue,
            Collection buffer) throws InterruptedException {
        Preconditions.checkNotNull(buffer);
        int added = queue.drainTo(buffer);
        if(added == 0) {
            // If the initial drain doesn't return any elements, we must
            // call #take in order to block until at least on element is
            // available
            buffer.add(queue.take());
            added += queue.drainTo(buffer);
            ++added;
        }
        return added;
    }

    /**
     * Perform the {@link BlockingQueue#drainTo(Collection)} operation, but
     * block for the specified {@code timeout} until at least one element is
     * available.
     * 
     * @param queue the {@link BlockingQueue} in which to perform the
     *            {@link BlockingQueue#drainTo(Collection) drainTo} method
     * @param buffer the collection into which the elements are drained
     * @return the number of elements that are drained
     */
    public static  int blockingDrain(BlockingQueue queue,
            Collection buffer, long timeout, TimeUnit unit) {
        Preconditions.checkNotNull(buffer);
        long deadline = System.nanoTime() + unit.toNanos(timeout);
        int added = queue.drainTo(buffer);
        try {
            if(added == 0) {
                E element = queue.poll(deadline - System.nanoTime(),
                        TimeUnit.NANOSECONDS);
                if(element != null) {
                    // If the element is null, it means we've waited long enough
                    // and no element has been added; otherwise, we need to
                    // check if more than one element was added
                    buffer.add(element);
                    added += queue.drainTo(buffer);
                    ++added;
                }
            }
        }
        catch (InterruptedException e) {
            throw CheckedExceptions.wrapAsRuntimeException(e);
        }
        return added;
    }

    private Queues() {/* noop */}

}