org.apache.flink.runtime.operators.resettable.NonReusingBlockResettableIterator Maven / Gradle / Ivy

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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.flink.runtime.operators.resettable;

import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable;
import org.apache.flink.runtime.memory.MemoryAllocationException;
import org.apache.flink.runtime.memory.MemoryManager;
import org.apache.flink.runtime.util.ResettableIterator;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

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

/**
 * 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 NonReusingBlockResettableIterator extends AbstractBlockResettableIterator
        implements ResettableIterator {

    public static final Logger LOG =
            LoggerFactory.getLogger(NonReusingBlockResettableIterator.class);

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

    protected Iterator input;

    protected T nextElement;

    protected T leftOverElement;

    protected boolean readPhase;

    protected boolean noMoreBlocks;

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

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

    public NonReusingBlockResettableIterator(
            MemoryManager memoryManager,
            TypeSerializer serializer,
            int numPages,
            AbstractInvokable ownerTask)
            throws MemoryAllocationException {
        super(serializer, memoryManager, numPages, ownerTask);
    }

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

    public void reopen(Iterator 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();
                    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();
    }
}