/*
 * Grapht, an open source dependency injector.
 * Copyright 2010-2012 Regents of the University of Minnesota and contributors
 *
 * This program 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 program 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 General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */
package org.grouplens.grapht.util;

import javax.inject.Provider;

/**
 * MemoizingProvider is a Provider that enforces memoization or caching on
 * another Provider that it wraps.
 * 
 * @author Michael Ludwig <mludwig@cs.umn.edu>
 * @param <T>
 */
public class MemoizingProvider<T> implements Provider<T> {
    private final Provider<T> wrapped;
    
    // We track a boolean because this supports providing null instances, in
    // which case we can't just check against null to see if we've already
    // queried the base provider
    private volatile T cached;
    private volatile boolean invoked;
    
    public MemoizingProvider(Provider<T> provider) {
        Preconditions.notNull("provider", provider);
        wrapped = provider;
        cached = null;
        invoked = false;
    }
    
    @Override
    public T get() {
        if (!invoked) {
            synchronized (this) {
                if (!invoked) {
                    cached = wrapped.get();
                    invoked = true;
                }
            }
        }
        return cached;
    }
}

@@ -891,16 +891,63 @@
 .util;%0A%0A
+import javax.annotation.concurrent.ThreadSafe;%0A
 import j
@@ -1085,17 +1085,30 @@
 raps.%0A *
- 
+%0A * @param %3CT%3E
 %0A * @aut
@@ -1153,23 +1153,21 @@
 %3E%0A *
- @param %3CT%3E%0A */
+/%0A@ThreadSafe
 %0Apub
@@ -1257,28 +1257,24 @@
 T%3E wrapped;%0A
-    
 %0A    // We t
@@ -1516,20 +1516,16 @@
 nvoked;%0A
-    
 %0A    pub
@@ -1705,20 +1705,16 @@
 ;%0A    %7D%0A
-    
 %0A    @Ov

Mark MemoizingProvider as thread-safe