| /* |
| * 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.tinkerpop.gremlin.process.traversal.step; |
| |
| import org.apache.tinkerpop.gremlin.process.computer.GraphComputer; |
| import org.apache.tinkerpop.gremlin.process.computer.traversal.TraversalVertexProgram; |
| import org.apache.tinkerpop.gremlin.process.traversal.step.util.ReducingBarrierStep; |
| |
| import java.util.NoSuchElementException; |
| |
| /** |
| * A Barrier is any step that requires all left traversers to be processed prior to emitting result traversers to the right. |
| * Note that some barrier steps may be "lazy" in that if their algorithm permits, they can emit right traversers prior to all traversers being aggregated. |
| * A barrier is the means by which a distributed step in {@link TraversalVertexProgram} is synchronized and made to behave a single step. |
| * All Barrier steps implement {@link MemoryComputing} as that is how barriers communicate with one another in {@link GraphComputer}. |
| * |
| * @author Marko A. Rodriguez (http://markorodriguez.com) |
| */ |
| public interface Barrier<B> extends MemoryComputing<B> { |
| |
| /** |
| * Process all left traversers by do not yield the resultant output. |
| * This method is useful for steps like {@link ReducingBarrierStep}, where traversers can be processed "on the fly" and thus, reduce memory consumption. |
| */ |
| public void processAllStarts(); |
| |
| /** |
| * Whether or not the step has an accessible barrier. |
| * |
| * @return whether a barrier exists or not |
| */ |
| public boolean hasNextBarrier(); |
| |
| /** |
| * Get the next barrier within this step. |
| * Barriers from parallel steps can be the be merged to create a single step with merge barriers. |
| * |
| * @return the next barrier of the step |
| * @throws NoSuchElementException |
| */ |
| public B nextBarrier() throws NoSuchElementException; |
| |
| /** |
| * Add a barrier to the step. |
| * This typically happens when multiple parallel barriers need to become one barrier at a single step. |
| * |
| * @param barrier the barrier to merge in |
| */ |
| public void addBarrier(final B barrier); |
| |
| /** |
| * A way to hard set that the barrier is complete. |
| * This is necessary when parallel barriers don't all have barriers and need hard resetting. |
| * The default implementation does nothing. |
| */ |
| public default void done() { |
| |
| } |
| } |