1 /*
2 * junixsocket
3 *
4 * Copyright 2009-2026 Christian Kohlschütter
5 *
6 * Licensed under the Apache License, Version 2.0 (the "License");
7 * you may not use this file except in compliance with the License.
8 * You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18 package org.newsclub.net.unix.memory;
19
20 import java.io.Closeable;
21 import java.io.IOException;
22
23 /**
24 * A mutually exclusive lock, which may or may not be reentrant.
25 *
26 * @author Christian Kohlschütter
27 */
28 public interface SharedMutex extends Closeable {
29 /**
30 * Try to lock the mutex.
31 * <p>
32 * Note that unless {@link #isReentrant()} is {@code}, trying to lock the mutex a second time will
33 * not succeed until someone else calls {@link #unlock()}
34 *
35 * @param timeoutMillis The timeout, in milliseconds, or {@code 0} for "try indefinitely".
36 * @return {@code true} if the lock was acquired.
37 * @throws IOException on error.
38 */
39 boolean tryLock(int timeoutMillis) throws IOException;
40
41 /**
42 * Unlocks the mutex.
43 * <p>
44 * By default, no ownership checks are performed.
45 *
46 * @throws IOException on error.
47 */
48 void unlock() throws IOException;
49
50 /**
51 * Reports if this lock instance is re-entrant, or not.
52 * <p>
53 * The value returned is constant.
54 *
55 * @return {@code true} if reentrant.
56 */
57 boolean isReentrant();
58
59 /**
60 * Reports if this lock instance can safely be accessed from multiple processes, or not. The
61 * actual way of accessing this {@link SharedMutex} is unspecified, but typically this is
62 * coordinated via {@link SharedMemory}.
63 * <p>
64 * The value returned is constant.
65 *
66 * @return {@code true} if inter-process access is permitted.
67 */
68 boolean isInterProcess();
69 }