--- /dev/null
+/*******************************************************************************\r
+ * Copyright (c) 2007, 2010 Association for Decentralized Information Management\r
+ * in Industry THTH ry.\r
+ * All rights reserved. This program and the accompanying materials\r
+ * are made available under the terms of the Eclipse Public License v1.0\r
+ * which accompanies this distribution, and is available at\r
+ * http://www.eclipse.org/legal/epl-v10.html\r
+ *\r
+ * Contributors:\r
+ * VTT Technical Research Centre of Finland - initial API and implementation\r
+ *******************************************************************************/\r
+package org.simantics.utils.datastructures.cache;\r
+\r
+import java.lang.ref.WeakReference;\r
+\r
+/**\r
+ * Caches the value provided by provider until the value has been garbage collected.\r
+ * <p>\r
+ * Cached IProvider provides the same instance as long as it is in memory.\r
+ * <p>\r
+ * Cached version is equal to original in hashCode/equals wise.\r
+ * \r
+ * @author Toni Kalajainen\r
+ */\r
+public class WeakCachedProvider<V> implements IProvider<V> {\r
+\r
+ public static final <V> IProvider<V> cache(IProvider<V> provider)\r
+ {\r
+ if (provider instanceof WeakCachedProvider<?>)\r
+ return provider;\r
+ return new WeakCachedProvider<V>(provider);\r
+ }\r
+\r
+ IProvider<V> provider;\r
+ WeakReference<V> ref;\r
+\r
+ WeakCachedProvider(IProvider<V> orig)\r
+ {\r
+ this.provider = orig;\r
+ }\r
+\r
+ @Override\r
+ public synchronized V get() throws ProvisionException {\r
+ if (ref!=null) {\r
+ V x = ref.get();\r
+ if (x==null) ref=null;\r
+ else return x;\r
+ }\r
+ V x = provider.get();\r
+ ref = new WeakReference<V>(x);\r
+ return x;\r
+ }\r
+\r
+ @Override\r
+ public int hashCode() {\r
+ return provider.hashCode();\r
+ }\r
+\r
+ @Override\r
+ public boolean equals(Object obj) {\r
+ return provider.equals(obj);\r
+ }\r
+\r
+}\r