/*
* 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.facebook.presto.operator;
import com.facebook.presto.spi.Page;
import com.facebook.presto.spi.block.Block;
import com.facebook.presto.spi.type.Type;
import com.google.common.collect.ImmutableList;
import com.google.common.util.concurrent.ListenableFuture;
import java.util.List;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
public class LimitOperator
implements Operator
{
public static class LimitOperatorFactory
implements OperatorFactory
{
private final int operatorId;
private final List<Type> types;
private final long limit;
private boolean closed;
public LimitOperatorFactory(int operatorId, List<? extends Type> types, long limit)
{
this.operatorId = operatorId;
this.types = ImmutableList.copyOf(types);
this.limit = limit;
}
@Override
public List<Type> getTypes()
{
return types;
}
@Override
public Operator createOperator(DriverContext driverContext)
{
checkState(!closed, "Factory is already closed");
OperatorContext operatorContext = driverContext.addOperatorContext(operatorId, LimitOperator.class.getSimpleName());
return new LimitOperator(operatorContext, types, limit);
}
@Override
public void close()
{
closed = true;
}
}
private final OperatorContext operatorContext;
private final List<Type> types;
private Page nextPage;
private long remainingLimit;
public LimitOperator(OperatorContext operatorContext, List<Type> types, long limit)
{
this.operatorContext = checkNotNull(operatorContext, "operatorContext is null");
this.types = checkNotNull(types, "types is null");
checkArgument(limit >= 0, "limit must be at least zero");
this.remainingLimit = limit;
}
@Override
public OperatorContext getOperatorContext()
{
return operatorContext;
}
@Override
public List<Type> getTypes()
{
return types;
}
@Override
public void finish()
{
remainingLimit = 0;
}
@Override
public boolean isFinished()
{
return remainingLimit == 0 && nextPage == null;
}
@Override
public ListenableFuture<?> isBlocked()
{
return NOT_BLOCKED;
}
@Override
public boolean needsInput()
{
return remainingLimit > 0 && nextPage == null;
}
@Override
public void addInput(Page page)
{
checkState(needsInput());
if (page.getPositionCount() <= remainingLimit) {
remainingLimit -= page.getPositionCount();
nextPage = page;
}
else {
Block[] blocks = new Block[page.getChannelCount()];
for (int channel = 0; channel < page.getChannelCount(); channel++) {
Block block = page.getBlock(channel);
blocks[channel] = block.getRegion(0, (int) remainingLimit);
}
nextPage = new Page((int) remainingLimit, blocks);
remainingLimit = 0;
}
}
@Override
public Page getOutput()
{
Page page = nextPage;
nextPage = null;
return page;
}
}