ObjectIndex: allow lazy registration of objects

ctrueden · ctrueden · commit 28a7e7cbc859 · 2013-11-22T16:40:00.000-06:00
diff --git a/src/main/java/org/scijava/object/LazyObjects.java b/src/main/java/org/scijava/object/LazyObjects.java
@@ -0,0 +1,52 @@
+/*
+ * #%L
+ * SciJava Common shared library for SciJava software.
+ * %%
+ * Copyright (C) 2009 - 2013 Board of Regents of the University of
+ * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
+ * Institute of Molecular Cell Biology and Genetics.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * 
+ * The views and conclusions contained in the software and documentation are
+ * those of the authors and should not be interpreted as representing official
+ * policies, either expressed or implied, of any organization.
+ * #L%
+ */
+
+package org.scijava.object;
+
+import java.util.Collection;
+
+/**
+ * Interface for objects created lazily. This interface provides a mechanism to
+ * register a callback of sorts, so that the {@link ObjectIndex} can request
+ * creation of objects only when they are needed.
+ * 
+ * @author Curtis Rueden
+ */
+public interface LazyObjects<T> {
+
+	/** Gets the collection of objects. */
+	Collection<T> get();
+
+}
diff --git a/src/main/java/org/scijava/object/ObjectIndex.java b/src/main/java/org/scijava/object/ObjectIndex.java
@@ -42,6 +42,7 @@
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.LinkedHashSet;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -87,6 +88,10 @@ public class ObjectIndex<E> implements Collection<E> {
 
 	private final Class<E> baseClass;
 
+	/** List of objects to add later as needed (i.e., lazily). */
+	private final List<LazyObjects<? extends E>> pending =
+		new LinkedList<LazyObjects<? extends E>>();
+
 	public ObjectIndex(final Class<E> baseClass) {
 		this.baseClass = baseClass;
 	}
@@ -127,12 +132,30 @@ public List<E> getAll() {
 	 *         list if no such objects exist (this method never returns null).
 	 */
 	public List<E> get(final Class<?> type) {
+		// lazily register any pending objects
+		if (!pending.isEmpty()) resolvePending();
+
 		List<E> list = retrieveList(type);
 		// NB: Return a copy of the data, to facilitate thread safety.
 		list = new ArrayList<E>(list);
 		return list;
 	}
 
+	/**
+	 * Registers objects which will be created lazily as needed.
+	 * <p>
+	 * This is useful if creation of the objects is expensive for some reason. In
+	 * that case, the object index can wait to actually request and register the
+	 * objects until the next accessor method invocation (i.e.,
+	 * {@link #get(Class)} or {@link #getAll()}).
+	 * </p>
+	 */
+	public void addLater(final LazyObjects<? extends E> c) {
+		synchronized (pending) {
+			pending.add(c);
+		}
+	}
+
 	// -- Collection methods --
 
 	@Override
@@ -361,6 +384,15 @@ protected List<E> retrieveList(final Class<?> type) {
 		return list;
 	}
 
+	private void resolvePending() {
+		synchronized (pending) {
+			while (!pending.isEmpty()) {
+				final LazyObjects<? extends E> c = pending.remove(0);
+				addAll(c.get());
+			}
+		}
+	}
+
 	// -- Helper classes --
 
 	private static class All {
