hyracks/hyracks-dataflow-std/src/main/java/edu/uci/ics/hyracks/dataflow/std/misc/LimitOperatorDescriptor.java

/*
 * Copyright 2009-2010 by The Regents of the University of California
 * 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 from
 * 
 *     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 edu.uci.ics.hyracks.dataflow.std.misc;

import java.nio.ByteBuffer;

import edu.uci.ics.hyracks.api.context.IHyracksTaskContext;
import edu.uci.ics.hyracks.api.dataflow.IOperatorNodePushable;
import edu.uci.ics.hyracks.api.dataflow.value.IRecordDescriptorProvider;
import edu.uci.ics.hyracks.api.dataflow.value.RecordDescriptor;
import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
import edu.uci.ics.hyracks.api.job.IOperatorDescriptorRegistry;
import edu.uci.ics.hyracks.dataflow.common.comm.io.FrameTupleAccessor;
import edu.uci.ics.hyracks.dataflow.common.comm.io.FrameTupleAppender;
import edu.uci.ics.hyracks.dataflow.common.comm.util.FrameUtils;
import edu.uci.ics.hyracks.dataflow.std.base.AbstractSingleActivityOperatorDescriptor;
import edu.uci.ics.hyracks.dataflow.std.base.AbstractUnaryInputUnaryOutputOperatorNodePushable;

public class LimitOperatorDescriptor extends AbstractSingleActivityOperatorDescriptor {
    private static final long serialVersionUID = 1L;
    private final int outputLimit;

    public LimitOperatorDescriptor(IOperatorDescriptorRegistry spec, RecordDescriptor rDesc, int outputLimit) {
        super(spec, 1, 1);
        recordDescriptors[0] = rDesc;
        this.outputLimit = outputLimit;
    }

    @Override
    public IOperatorNodePushable createPushRuntime(final IHyracksTaskContext ctx,
            final IRecordDescriptorProvider recordDescProvider, int partition, int nPartitions)
            throws HyracksDataException {

        return new AbstractUnaryInputUnaryOutputOperatorNodePushable() {
            private FrameTupleAccessor fta;
            private int currentSize;
            private boolean finished;

            @Override
            public void open() throws HyracksDataException {
                fta = new FrameTupleAccessor(ctx.getFrameSize(), recordDescriptors[0]);
                currentSize = 0;
                finished = false;
                writer.open();
            }

            @Override
            public void nextFrame(ByteBuffer buffer) throws HyracksDataException {
                if (!finished) {
                    fta.reset(buffer);
                    int count = fta.getTupleCount();
                    if ((currentSize + count) > outputLimit) {
                        ByteBuffer b = ctx.allocateFrame();
                        FrameTupleAppender partialAppender = new FrameTupleAppender(ctx.getFrameSize());
                        partialAppender.reset(b, true);
                        int copyCount = outputLimit - currentSize;
                        for (int i = 0; i < copyCount; i++) {
                            partialAppender.append(fta, i);
                            currentSize++;
                        }
                        FrameUtils.makeReadable(b);
                        FrameUtils.flushFrame(b, writer);
                        finished = true;
                    } else {
                        FrameUtils.flushFrame(buffer, writer);
                        currentSize += count;
                    }
                }
            }

            @Override
            public void fail() throws HyracksDataException {
                writer.fail();

            }

            @Override
            public void close() throws HyracksDataException {
                writer.close();
            }
        };
    }

}