01: /*
02: * <copyright>
03: *
04: * Copyright 1997-2004 BBNT Solutions, LLC
05: * under sponsorship of the Defense Advanced Research Projects
06: * Agency (DARPA).
07: *
08: * You can redistribute this software and/or modify it under the
09: * terms of the Cougaar Open Source License as published on the
10: * Cougaar Open Source Website (www.cougaar.org).
11: *
12: * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
13: * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
14: * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
15: * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
16: * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
17: * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
18: * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
22: * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
23: *
24: * </copyright>
25: */
26: package org.cougaar.util;
27:
28: /** LockFlag class adapted from sample in "Java Threads"
29: * -- Scott Oaks and Henry Wong. O'Reilly, Jan 1997
30: **/
31:
32: public class LockFlag {
33: private Thread busyflag = null;
34: private int busycount = 0;
35:
36: private static LockFlag defaultLock = new LockFlag();
37:
38: /** Returns a single VM-scoped LockFlag instance which can
39: * be shared amongst many threads
40: **/
41: public static LockFlag getDefaultLock() {
42: return defaultLock;
43: }
44:
45: public synchronized void getBusyFlag() {
46: while (tryGetBusyFlag() == false) {
47: try {
48: wait();
49: } catch (Exception e) {
50: }
51: }
52: }
53:
54: public synchronized boolean tryGetBusyFlag() {
55: if (busyflag == null) {
56: busyflag = Thread.currentThread();
57: busycount = 1;
58: return true;
59: }
60: if (busyflag == Thread.currentThread()) {
61: busycount++;
62: return true;
63: }
64: return false;
65: }
66:
67: /** @return true on success.
68: **/
69: public synchronized boolean freeBusyFlag() {
70: if (getBusyFlagOwner() == Thread.currentThread()) {
71: busycount--;
72: if (busycount == 0) {
73: busyflag = null;
74: notify();
75: }
76: return true;
77: } else {
78: return false;
79: }
80: }
81:
82: public synchronized Thread getBusyFlagOwner() {
83: return busyflag;
84: }
85:
86: public int getBusyCount() {
87: return busycount;
88: }
89:
90: }
|