eu.stratosphere.pact.runtime.resettable.BlockResettableIterator.java Source code

Introduction

Here is the source code for eu.stratosphere.pact.runtime.resettable.BlockResettableIterator.java

Source

/***********************************************************************************************************************
 * Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
 *
 * 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 eu.stratosphere.pact.runtime.resettable;

import java.io.IOException;
import java.util.Iterator;
import java.util.NoSuchElementException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import eu.stratosphere.api.common.typeutils.TypeSerializer;
import eu.stratosphere.nephele.services.memorymanager.MemoryAllocationException;
import eu.stratosphere.nephele.services.memorymanager.MemoryManager;
import eu.stratosphere.nephele.template.AbstractInvokable;
import eu.stratosphere.pact.runtime.util.ResettableIterator;

/**
 * Implementation of an iterator that fetches a block of data into main memory and offers resettable
 * access to the data in that block.
 * 
 */
public class BlockResettableIterator<T> extends AbstractBlockResettableIterator<T>
        implements ResettableIterator<T> {

    public static final Log LOG = LogFactory.getLog(BlockResettableIterator.class);

    // ------------------------------------------------------------------------

    protected Iterator<T> input;

    private T nextElement;

    private final T reuseElement;

    private T leftOverElement;

    private boolean readPhase;

    private boolean noMoreBlocks;

    // ------------------------------------------------------------------------

    public BlockResettableIterator(MemoryManager memoryManager, Iterator<T> input, TypeSerializer<T> serializer,
            int numPages, AbstractInvokable ownerTask) throws MemoryAllocationException {
        this(memoryManager, serializer, numPages, ownerTask);
        this.input = input;
    }

    public BlockResettableIterator(MemoryManager memoryManager, TypeSerializer<T> serializer, int numPages,
            AbstractInvokable ownerTask) throws MemoryAllocationException {
        super(serializer, memoryManager, numPages, ownerTask);

        this.reuseElement = serializer.createInstance();
    }

    // ------------------------------------------------------------------------

    public void reopen(Iterator<T> input) throws IOException {
        this.input = input;

        this.noMoreBlocks = false;
        this.closed = false;

        nextBlock();
    }

    @Override
    public boolean hasNext() {
        try {
            if (this.nextElement == null) {
                if (this.readPhase) {
                    // read phase, get next element from buffer
                    T tmp = getNextRecord(this.reuseElement);
                    if (tmp != null) {
                        this.nextElement = tmp;
                        return true;
                    } else {
                        return false;
                    }
                } else {
                    if (this.input.hasNext()) {
                        final T next = this.input.next();
                        if (writeNextRecord(next)) {
                            this.nextElement = next;
                            return true;
                        } else {
                            this.leftOverElement = next;
                            return false;
                        }
                    } else {
                        this.noMoreBlocks = true;
                        return false;
                    }
                }
            } else {
                return true;
            }
        } catch (IOException ioex) {
            throw new RuntimeException("Error (de)serializing record in block resettable iterator.", ioex);
        }
    }

    @Override
    public T next() {
        if (this.nextElement == null) {
            if (!hasNext()) {
                throw new NoSuchElementException();
            }
        }

        T out = this.nextElement;
        this.nextElement = null;
        return out;
    }

    @Override
    public void remove() {
        throw new UnsupportedOperationException();
    }

    public void reset() {
        // a reset always goes to the read phase
        this.readPhase = true;
        super.reset();
    }

    @Override
    public boolean nextBlock() throws IOException {
        // check the state
        if (this.closed) {
            throw new IllegalStateException("Iterator has been closed.");
        }

        // check whether more blocks are available
        if (this.noMoreBlocks) {
            return false;
        }

        // reset the views in the superclass
        super.nextBlock();

        T next = this.leftOverElement;
        this.leftOverElement = null;
        if (next == null) {
            if (this.input.hasNext()) {
                next = this.input.next();
            } else {
                this.noMoreBlocks = true;
                return false;
            }
        }

        // write the leftover record
        if (!writeNextRecord(next)) {
            throw new IOException("BlockResettableIterator could not serialize record into fresh memory block: "
                    + "Record is too large.");
        }

        this.nextElement = next;
        this.readPhase = false;

        return true;
    }

    /**
     * Checks, whether the input that is blocked by this iterator, has further elements
     * available. This method may be used to forecast (for example at the point where a
     * block is full) whether there will be more data (possibly in another block).
     * 
     * @return True, if there will be more data, false otherwise.
     */
    public boolean hasFurtherInput() {
        return !this.noMoreBlocks;
    }

    public void close() {
        // suggest that we are in the read phase. because nothing is in the current block,
        // read requests will fail
        this.readPhase = true;
        super.close();
    }
}