Resolved issue: NETTY-93 (ChannelLocal (as a counterpart of ThreadLocal))

* Added ChannelLocal
* Added ConcurrentWeakHashMap

src/main/java/org/jboss/netty/channel/ChannelLocal.java

@@ -0,0 +1,64 @@
+/*
+ * JBoss, Home of Professional Open Source
+ *
+ * Copyright 2008, Red Hat Middleware LLC, and individual contributors
+ * by the @author tags. See the COPYRIGHT.txt in the distribution for a
+ * full listing of individual contributors.
+ *
+ * This 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 software 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this software; if not, write to the Free
+ * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
+ * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
+ */
+package org.jboss.netty.channel;
+
+import java.util.concurrent.ConcurrentMap;
+
+import org.jboss.netty.util.ConcurrentWeakHashMap;
+
+/**
+ * @author The Netty Project (netty-dev@lists.jboss.org)
+ * @author Trustin Lee (tlee@redhat.com)
+ * @version $Rev$, $Date$
+ */
+public class ChannelLocal<T> {
+    private final ConcurrentMap<Channel, T> map = new ConcurrentWeakHashMap<Channel, T>();
+
+    protected T initialValue(@SuppressWarnings("unused") Channel channel) {
+        return null;
+    }
+
+    public T get(Channel channel) {
+        T value = map.get(channel);
+        if (value == null) {
+            value = initialValue(channel);
+            T oldValue = setIfAbsent(channel, value);
+            if (oldValue != null) {
+                value = oldValue;
+            }
+        }
+        return value;
+    }
+
+    public T set(Channel channel, T newValue) {
+        return map.put(channel, newValue);
+    }
+
+    public T setIfAbsent(Channel channel, T value) {
+        return map.putIfAbsent(channel, value);
+    }
+
+    public T remove(Channel channel) {
+        return map.remove(channel);
+    }
+}