Fixed javadoc warning; added shared executor/timer wrappers to prevent inadvertent shutdown; added shutdown to CoreManager.deactivate.

Change-Id: I27f31b5d41050d6d87cd6419ab863201c4585843
diff --git a/utils/misc/src/main/java/org/onlab/util/SharedExecutorService.java b/utils/misc/src/main/java/org/onlab/util/SharedExecutorService.java
new file mode 100644
index 0000000..2cfdb5a
--- /dev/null
+++ b/utils/misc/src/main/java/org/onlab/util/SharedExecutorService.java
@@ -0,0 +1,138 @@
+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onlab.util;
+
+import java.util.Collection;
+import java.util.List;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+/**
+ * Executor service wrapper for shared executors with safeguards on shutdown
+ * to prevent inadvertent shutdown.
+ */
+class SharedExecutorService implements ExecutorService {
+
+    private static final String NOT_ALLOWED = "Shutdown of shared executor is not allowed";
+
+    private ExecutorService executor;
+
+    /**
+     * Creates a wrapper for the given executor service.
+     *
+     * @param executor executor service to wrap
+     */
+    SharedExecutorService(ExecutorService executor) {
+        this.executor = executor;
+    }
+
+    /**
+     * Returns the backing executor service.
+     *
+     * @return backing executor service
+     */
+    ExecutorService backingExecutor() {
+        return executor;
+    }
+
+    /**
+     * Swaps the backing executor with a new one and shuts down the old one.
+     *
+     * @param executor new executor service
+     */
+    void setBackingExecutor(ExecutorService executor) {
+        ExecutorService oldExecutor = this.executor;
+        this.executor = executor;
+        oldExecutor.shutdown();
+    }
+
+    @Override
+    public void shutdown() {
+        throw new UnsupportedOperationException(NOT_ALLOWED);
+    }
+
+    @Override
+    public List<Runnable> shutdownNow() {
+        throw new UnsupportedOperationException(NOT_ALLOWED);
+    }
+
+    @Override
+    public boolean isShutdown() {
+        return executor.isShutdown();
+    }
+
+    @Override
+    public boolean isTerminated() {
+        return executor.isTerminated();
+    }
+
+    @Override
+    public boolean awaitTermination(long timeout, TimeUnit unit)
+            throws InterruptedException {
+        return executor.awaitTermination(timeout, unit);
+    }
+
+    @Override
+    public <T> Future<T> submit(Callable<T> task) {
+        return executor.submit(task);
+    }
+
+    @Override
+    public <T> Future<T> submit(Runnable task, T result) {
+        return executor.submit(task, result);
+    }
+
+    @Override
+    public Future<?> submit(Runnable task) {
+        return executor.submit(task);
+    }
+
+    @Override
+    public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
+            throws InterruptedException {
+        return executor.invokeAll(tasks);
+    }
+
+    @Override
+    public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
+                                         long timeout, TimeUnit unit)
+            throws InterruptedException {
+        return executor.invokeAll(tasks, timeout, unit);
+    }
+
+    @Override
+    public <T> T invokeAny(Collection<? extends Callable<T>> tasks)
+            throws InterruptedException, ExecutionException {
+        return executor.invokeAny(tasks);
+    }
+
+    @Override
+    public <T> T invokeAny(Collection<? extends Callable<T>> tasks,
+                           long timeout, TimeUnit unit)
+            throws InterruptedException, ExecutionException, TimeoutException {
+        return invokeAny(tasks, timeout, unit);
+    }
+
+    @Override
+    public void execute(Runnable command) {
+        executor.execute(command);
+    }
+
+}