1 /*
2 * This file is part of Waarp Project (named also Waarp or GG).
3 *
4 * Copyright (c) 2019, Waarp SAS, and individual contributors by the @author
5 * tags. See the COPYRIGHT.txt in the distribution for a full listing of
6 * individual contributors.
7 *
8 * All Waarp Project is free software: you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation, either version 3 of the License, or (at your
11 * option) any later version.
12 *
13 * Waarp is distributed in the hope that it will be useful, but WITHOUT ANY
14 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
15 * A PARTICULAR PURPOSE. See the GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License along with
18 * Waarp . If not, see <http://www.gnu.org/licenses/>.
19 */
20 package org.waarp.gateway.ftp.config;
21
22 import java.util.concurrent.atomic.AtomicInteger;
23
24 /**
25 * Circular Value used by passive connections to find the next valid port to
26 * propose to the client.
27 */
28 class CircularIntValue {
29 private final Object syncObject = new Object();
30 /**
31 * Min value
32 */
33 private final int min;
34
35 /**
36 * Max value
37 */
38 private final int max;
39
40 /**
41 * Current Value
42 */
43 private final AtomicInteger current;
44
45 /**
46 * Create a circular range of values
47 *
48 * @param min
49 * @param max
50 */
51 CircularIntValue(final int min, final int max) {
52 this.min = min;
53 this.max = max;
54 current = new AtomicInteger(this.min - 1);
55 }
56
57 /**
58 * Get the next value
59 *
60 * @return the next value
61 */
62 public final int getNext() {
63 synchronized (syncObject) {
64 if (!current.compareAndSet(max, min)) {
65 current.incrementAndGet();
66 }
67 return current.get();
68 }
69 }
70 }