added a pseudo list implementation as this is often useful.

Using java.util.concurrent.CopyOnWriteList would be problematic because of retrotranslator.


git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@1638 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/util/CopyOnWriteList.java

+package hudson.util;
+
+import java.util.List;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Iterator;
+
+/**
+ * {@link List}-like implementation that has copy-on-write semantics.
+ *
+ * <p>
+ * This class is suitable where the write operation is relatively uncommon.
+ *
+ * @author Kohsuke Kawaguchi
+ */
+public class CopyOnWriteList<E> implements Iterable<E> {
+    private volatile List<E> core;
+
+    public CopyOnWriteList(List<E> core) {
+        this.core = new ArrayList<E>(core);
+    }
+
+    public CopyOnWriteList() {
+        this.core = Collections.emptyList();
+    }
+
+    public synchronized void add(E e) {
+        List<E> n = new ArrayList<E>(core);
+        n.add(e);
+        core = n;
+    }
+
+    /**
+     * Removes an item from the list.
+     *
+     * @return
+     *      true if the list contained the item. False if it didn't,
+     *      in which case there's no change.
+     */
+    public synchronized boolean remove(E e) {
+        List<E> n = new ArrayList<E>(core);
+        boolean r = n.remove(e);
+        core = n;
+        return r;
+    }
+
+    public Iterator<E> iterator() {
+        return core.iterator();
+    }
+}