org.eclipse.osgi.internal.container.AtomicLazyInitializer Maven / Gradle / Ivy

Show more of this group Show more artifacts with this name
Show all versions of aspectjtools Show documentation

AspectJ tools most notably contains the AspectJ compiler (AJC). AJC applies aspects to Java classes during compilation, fully replacing Javac for plain Java classes and also compiling native AspectJ or annotation-based @AspectJ syntax. Furthermore, AJC can weave aspects into existing class files in a post-compile binary weaving step. This library is a superset of AspectJ weaver and hence also of AspectJ runtime.

There is a newer version: 1.9.22.1

Show newest version

/*******************************************************************************
 * Copyright (c) 2014, 2021 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.osgi.internal.container;

import java.util.concurrent.Callable;
import java.util.concurrent.atomic.AtomicReference;

/**
 * A helper class for doing lazy initialization
 *
 * @param  the type of object to lazy initialize
 */
public class AtomicLazyInitializer {
	private final AtomicReference holder = new AtomicReference<>();

	/**
	 * Gets the current value.  If the value has not been initialized then
	 * {@code null} is returned;
	 * @return the current value
	 */
	public final V get() {
		return holder.get();
	}

	/**
	 * Atomically gets the current initialized value.  If the current value is {@code null}
	 * then the supplied initializer is called to create the value returned.
	 * @param initializer the initializer to call if the current value is {@code null}
	 * @return the initialized value.  May return {@code null} if initializer returns null.
	 */
	public final V getInitialized(Callable initializer) {
		V result = holder.get();
		if (result != null) {
			return result;
		}
		// Must hold a lock to ensure the operation is atomic.
		synchronized (holder) {
			result = holder.get();
			if (result != null) {
				return result;
			}
			try {
				result = initializer.call();
			} catch (Exception e) {
				unchecked(e);
			}
			holder.set(result);
			return result;
		}
	}

	/**
	 * Gets the current value and clears the value for future calls to this lazy initializer.
	 * @return the current value
	 */
	public final V getAndClear() {
		return holder.getAndSet(null);
	}

	private static  T unchecked(Exception exception) {
		return AtomicLazyInitializer.unchecked0(exception);
	}

	@SuppressWarnings("unchecked")
	private static  T unchecked0(Exception exception) throws E {
		throw (E) exception;
	}
}