com.hazelcast.jet.core.AppendableTraverser Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2021, Hazelcast, Inc. All Rights Reserved.
*
* 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.hazelcast.jet.core;
import com.hazelcast.jet.Traverser;
import javax.annotation.Nonnull;
import java.util.ArrayDeque;
/**
* A traverser with an internal {@link ArrayDeque}. You can efficiently {@link
* #append} items to it that will be later traversed.
*
* It's useful to be returned from a flat-mapping function when an item is
* flat-mapped to a small number of items:
*
{@code
* Traverser at = new AppendableTraverser(2);
* Traverser t = Traverser.over(10, 20)
* .flatMap(item -> {
* at.append(item);
* at.append(item + 1);
* return at;
* });
* }
* The {@code t} traverser above will output {10, 11, 20, 21}. This approach
* reduces the GC pressure by avoiding the allocation of a new traverser for
* each item that will traverse over just a few or even zero items.
*
* See {@link ResettableSingletonTraverser} if you have at most one item to
* traverse.
*
* @param item type
*
* @since Jet 3.0
*/
public class AppendableTraverser implements Traverser {
private final ArrayDeque queue;
/**
* Creates an appendable traverser.
*/
public AppendableTraverser(int initialCapacity) {
queue = new ArrayDeque<>(initialCapacity);
}
/**
* {@inheritDoc}
* @return {@code this} instance
*/
@Nonnull @Override
public AppendableTraverser append(@Nonnull T item) {
queue.add(item);
return this;
}
@Override
public T next() {
return queue.poll();
}
/**
* Returns {@code true}, if the next call to {@link #next} will return
* {@code null}.
*/
public boolean isEmpty() {
return queue.isEmpty();
}
}