The BooleanLock class provides a useful encapsulation of a boolean variable that is easily and safely accessed from multiple theads.
/*
* Copyright 2005 MBARI
*
* Licensed under the GNU LESSER GENERAL PUBLIC LICENSE, Version 2.1
* (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.gnu.org/copyleft/lesser.html
*
* 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.mbari.util;
//~--- classes ----------------------------------------------------------------
/**
* <p>The BooleanLock class provides a useful encapsulation of a boolean variable
* that is easily and safely accessed from multiple theads. These threads can
* test and set an internal value and wait for it to change. The wait/notify
* mechanism is used internally to support waiting for the value to change, and
* frees external classes from the error-prone complexity of properly implementing this mechanism.</p>
*
*@author <a href="http://www.mbari.org">MBARI</a>
*@version $Id: BooleanLock.java 332 2006-08-01 18:38:46Z hohonuuli $
*/
public class BooleanLock {
/**
* @uml.property name="value"
*/
private boolean value;
//~--- constructors -------------------------------------------------------
/**
* Constructor. Assigns the inital value to false.
*/
public BooleanLock() {
this(false);
}
/**
* Constructor
*
* @param initialValue The intial value to assign to the BooleanLock
*/
public BooleanLock(boolean initialValue) {
value = initialValue;
}
//~--- get methods --------------------------------------------------------
/**
* @return true if the lock value is false
*/
public synchronized boolean isFalse() {
return !value;
}
/**
* @return true if the lock value is true
*/
public synchronized boolean isTrue() {
return value;
}
//~--- set methods --------------------------------------------------------
/**
* Sets the value of this lock. Issues a notifyAll() call if the value is changed. (i.e the new value does not equal the current value.
* @param newValue
* @uml.property name="value"
*/
public synchronized void setValue(boolean newValue) {
if (newValue != value) {
value = newValue;
notifyAll();
}
}
//~--- methods ------------------------------------------------------------
/**
* Attempts to change the value of the lock to false. This method will wait
* for the specified duration until attempting the change.
*
* @param msTimeout The time (in milliseconds) to wait before changing the value to true
* @return True is the change is a success
* @throws InterruptedException
*/
public synchronized boolean waitToSetFalse(long msTimeout)
throws InterruptedException {
boolean success = waitUntilTrue(msTimeout);
if (success) {
setValue(false);
}
return success;
}
/**
* Attempts to change the value of the lock to true. This method will wait
* for the specified duration until attempting the change.
*
* @param msTimeout The time (in milliseconds) to wait before changing the value to true
* @return True is the change is a success
* @throws InterruptedException
*/
public synchronized boolean waitToSetTrue(long msTimeout)
throws InterruptedException {
boolean success = waitUntilFalse(msTimeout);
if (success) {
setValue(true);
}
return success;
}
/**
* @param msTimeout
* @return
* @throws InterruptedException
*/
public synchronized boolean waitUntilFalse(long msTimeout)
throws InterruptedException {
return waitUntilStateIs(false, msTimeout);
}
/**
* @param state
* @param msTimeout
* @return
* @throws InterruptedException
*/
public synchronized boolean waitUntilStateIs(boolean state, long msTimeout)
throws InterruptedException {
if (msTimeout == 0L) {
while (value != state) {
wait();
// wait indefinitely until notified
}
// condition has finally been met
return true;
}
// only wait for the specified amount of time
long endTime = System.currentTimeMillis() + msTimeout;
long msRemaining = msTimeout;
while ((value != state) && (msRemaining > 0L)) {
wait(msRemaining);
msRemaining = endTime - System.currentTimeMillis();
}
// May have timed out, or value may have met value, calculate return
// value
return (value == state);
}
/**
* @param msTimeout
* @return
* @throws InterruptedException
*/
public synchronized boolean waitUntilTrue(long msTimeout)
throws InterruptedException {
return waitUntilStateIs(true, msTimeout);
}
}
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