content: /*
   * Copyright (C) 2012-2016 Markus Junginger, greenrobot (http://greenrobot.org)
   *
   * 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 org.greenrobot.eventbus;
  
  final class PendingPostQueue {
    private PendingPost head;
    private PendingPost tail;
  
    synchronized void enqueue(PendingPost pendingPost) {
      if (pendingPost == null) {
        throw new NullPointerException("null cannot be enqueued");
      }
      if (tail != null) {
        tail.next = pendingPost;
        tail = pendingPost;
      } else if (head == null) {
        head = tail = pendingPost;
      } else {
        throw new IllegalStateException("Head present, but no tail");
      }
      notifyAll();
    }
  
    synchronized PendingPost poll() {
      PendingPost pendingPost = head;
      if (head != null) {
        head = head.next;
        if (head == null) {
          tail = null;
        }
      }
      return pendingPost;
    }
  
    synchronized PendingPost poll(int maxMillisToWait) throws InterruptedException {
      if (head == null) {
        wait(maxMillisToWait);
      }
      return poll();
    }
  }
  