runtime/master/src/main/java/org/apache/nemo/runtime/master/scheduler/PendingTaskCollectionPointer.java

/*
 * 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.nemo.runtime.master.scheduler;

import net.jcip.annotations.ThreadSafe;
import org.apache.nemo.runtime.common.plan.Task;

import javax.inject.Inject;
import java.util.Collection;
import java.util.Optional;

/**
 * Points to a collection of pending tasks eligible for scheduling.
 * This pointer effectively points to a subset of a scheduling group.
 * Within the collection, the tasks can be scheduled in any order.
 */
@ThreadSafe
public final class PendingTaskCollectionPointer {
  private Collection<Task> curTaskCollection;

  @Inject
  private PendingTaskCollectionPointer() {
  }

  /**
   * This collection of tasks should take precedence over any previous collection of tasks.
   *
   * @param newCollection to schedule.
   */
  synchronized void setToOverwrite(final Collection<Task> newCollection) {
    this.curTaskCollection = newCollection;
  }

  /**
   * This collection of tasks can be scheduled only if there's no collection of tasks to schedule at the moment.
   *
   * @param newCollection to schedule
   */
  synchronized void setIfNull(final Collection<Task> newCollection) {
    if (this.curTaskCollection == null) {
      this.curTaskCollection = newCollection;
    }
  }

  /**
   * Take the whole collection of tasks to schedule, and set the pointer to null.
   *
   * @return optional tasks to schedule
   */
  synchronized Optional<Collection<Task>> getAndSetNull() {
    final Collection<Task> cur = curTaskCollection;
    curTaskCollection = null;
    return Optional.ofNullable(cur);
  }
}