Bug 449779 - Deadlock within the OSGi framework

 - Introduce  and use AtomicLazyInitializer to manage construction of the loader
 - Remove the monitor lock from ModuleWiring

1 files changed, 76 insertions, 0 deletions

diff --git a/bundles/org.eclipse.osgi/container/src/org/eclipse/osgi/internal/container/AtomicLazyInitializer.java b/bundles/org.eclipse.osgi/container/src/org/eclipse/osgi/internal/container/AtomicLazyInitializer.java
new file mode 100644
index 000000000..bb72070d5
--- /dev/null
+++ b/bundles/org.eclipse.osgi/container/src/org/eclipse/osgi/internal/container/AtomicLazyInitializer.java
@@ -0,0 +1,76 @@
+/*******************************************************************************
+ * Copyright (c) 2014 IBM Corporation and others.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ * 
+ * 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 <V> the type of object to lazy initialize
+ */
+public class AtomicLazyInitializer<V> {
+	private final AtomicReference<V> holder = new AtomicReference<V>();
+
+	/**
+	 * 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<V> 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> T unchecked(Exception exception) {
+		return AtomicLazyInitializer.<T, RuntimeException> unchecked0(exception);
+	}
+
+	@SuppressWarnings("unchecked")
+	private static <T, E extends Exception> T unchecked0(Exception exception) throws E {
+		throw (E) exception;
+	}
+}
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