cosmos.results.CloseableIterable.java Source code

Introduction

Here is the source code for cosmos.results.CloseableIterable.java

Source

/**
 * 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.
 *
 *  Copyright 2013 Josh Elser
 *
 */
package cosmos.results;

import static com.google.common.base.Preconditions.checkNotNull;

import java.util.Iterator;
import java.util.Map.Entry;
import java.util.concurrent.TimeUnit;

import org.apache.accumulo.core.client.ScannerBase;
import org.apache.accumulo.core.data.Key;
import org.apache.accumulo.core.data.Value;

import com.google.common.base.Function;
import com.google.common.base.Predicate;
import com.google.common.base.Stopwatch;
import com.google.common.collect.Iterables;

import cosmos.trace.Tracer;

/**
 * 
 */
public class CloseableIterable<T> implements Results<T> {

    protected final ScannerBase scanner;
    protected final Iterable<T> iterable;
    protected final Tracer tracer;
    protected final String description;
    protected final Stopwatch sw;
    protected boolean closed = false;

    public CloseableIterable(ScannerBase scanner, Iterable<T> iterable, Tracer t, String desc, Stopwatch sw) {
        checkNotNull(scanner);
        checkNotNull(iterable);
        checkNotNull(t);
        checkNotNull(desc);
        checkNotNull(sw);

        this.scanner = scanner;
        this.iterable = iterable;
        this.tracer = t;
        this.description = desc;
        this.sw = sw;
    }

    public static <T> CloseableIterable<T> create(ScannerBase scanner, Iterable<T> iterable, Tracer t, String desc,
            Stopwatch sw) {
        return new CloseableIterable<T>(scanner, iterable, t, desc, sw);
    }

    public static <T> CloseableIterable<T> transform(ScannerBase scanner, Function<Entry<Key, Value>, T> func,
            Tracer t, String desc, Stopwatch sw) {
        return new CloseableIterable<T>(scanner, Iterables.transform(scanner, func), t, desc, sw);
    }

    public static <T> CloseableIterable<T> filterAndTransform(ScannerBase scanner,
            Predicate<Entry<Key, Value>> filter, Function<Entry<Key, Value>, T> func, Tracer t, String desc,
            Stopwatch sw) {
        return new CloseableIterable<T>(scanner, Iterables.transform(Iterables.filter(scanner, filter), func), t,
                desc, sw);
    }

    protected ScannerBase source() {
        return scanner;
    }

    @Override
    public Iterator<T> iterator() {
        return new Iterator<T>() {
            final Iterator<T> delegate = iterable.iterator();

            @Override
            public boolean hasNext() {
                boolean hasNext = delegate.hasNext();

                if (!hasNext && sw.isRunning()) {
                    sw.stop();
                    tracer.addTiming(description, sw.elapsed(TimeUnit.MILLISECONDS));

                    // TODO Is there a detriment of auto-closing this here?
                    // It doesn't make sense for more than one client to read off of one ScannerBase
                    // so we likely also don't have to add any synchronization
                    scanner.close();
                    closed = true;
                }

                return hasNext;
            }

            @Override
            public T next() {
                return delegate.next();
            }

            @Override
            public void remove() {
                delegate.remove();
            }

        };
    }

    @Override
    public void close() {
        // Client may close the Iterable before exhausting the records
        if (sw.isRunning()) {
            sw.stop();
            tracer.addTiming(description, sw.elapsed(TimeUnit.MILLISECONDS));
        }

        if (!closed) {
            scanner.close();
            closed = true;
        }
    }

}