jolie.util.Lazy Maven / Gradle / Ivy
/*
* Copyright (C) 2024 Fabrizio Montesi
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
* MA 02110-1301 USA
*/
package jolie.util;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.Supplier;
/**
* Utility class to store lazily-instantiated values.
*
* @author Fabrizio Montesi
* @param the type of the stored value
*/
public class Lazy< T > implements Supplier< T > {
private volatile Supplier< T > contentSupplier;
/**
* Constructor
*
* @param initSupplier code for initialising the value the first time it is requested
*/
public Lazy( Supplier< T > initSupplier ) {
contentSupplier = new Supplier<>() {
private final ReentrantLock lock = new ReentrantLock();
@Override
public T get() {
lock.lock();
try {
if( contentSupplier == this ) {
T content = initSupplier.get();
contentSupplier = () -> content;
}
} finally {
lock.unlock();
}
return contentSupplier.get();
}
};
}
/**
* Get the present value, or initialise a new one if not already present
*/
@Override
public T get() {
return contentSupplier.get();
}
}