1 /*
2 * Licensed to The Apereo Foundation under one or more contributor license
3 * agreements. See the NOTICE file distributed with this work for additional
4 * information regarding copyright ownership.
5 *
6 *
7 * The Apereo Foundation licenses this file to you under the Educational
8 * Community License, Version 2.0 (the "License"); you may not use this file
9 * except in compliance with the License. You may obtain a copy of the License
10 * at:
11 *
12 * http://opensource.org/licenses/ecl2.txt
13 *
14 * Unless required by applicable law or agreed to in writing, software
15 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
16 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
17 * License for the specific language governing permissions and limitations under
18 * the License.
19 *
20 */
21
22 package org.opencastproject.util;
23
24 import java.util.Optional;
25 import java.util.concurrent.Callable;
26 import java.util.concurrent.atomic.AtomicBoolean;
27
28 /** Only one function application can be threaded through the needle eye at a time. */
29 public final class NeedleEye {
30 private final AtomicBoolean running = new AtomicBoolean(false);
31
32 /**
33 * Apply function <code>f</code> only if no other thread currently applies a function using this needle eye.
34 *
35 * @return the result of <code>f</code> or none if another function is currently being applied.
36 */
37 public <A> Optional<A> apply(Callable<A> f) {
38 if (running.compareAndSet(false, true)) {
39 try {
40 return Optional.ofNullable(f.call());
41 } catch (Exception e) {
42 throw new RuntimeException("Exception in NeedleEye function", e);
43 } finally {
44 running.set(false);
45 }
46 } else {
47 return Optional.empty();
48 }
49 }
50 }