Add MessageList.array() / Rewrite MessageList.add(T[], int, int)

- MessageList.array() should give better performance + concise code
- MessageList.add(T[], int, int) iterated over the source array 3 times at worst case. This commit reduces that to 1 time.

transport/src/main/java/io/netty/channel/MessageList.java

@@ -253,23 +253,53 @@ public final class MessageList<T> implements Iterable<T> {
      * and return itself.
      */
     public MessageList<T> add(T[] src, int srcIdx, int srcLen) {
-        checkElements(src, srcIdx, srcLen);
+        if (src == null) {
+            throw new NullPointerException("src");
+        }
 
         modifications ++;
-        int oldSize = size;
-        int newSize = oldSize + srcLen;
+
+        int dstIdx = size;
+        final int newSize = dstIdx + srcLen;
         ensureCapacity(newSize);
-        System.arraycopy(src, srcIdx, elements, oldSize, srcLen);
-        size = newSize;
+
+        final int srcEndIdx = srcIdx + srcLen;
+        int i = srcIdx;
+        try {
             if (byteBufsOnly) {
-            for (int i = srcIdx; i < srcIdx; i++) {
-                if (!(src[i] instanceof ByteBuf)) {
+                for (; i < srcEndIdx; i ++) {
+                    T m = src[srcIdx];
+                    if (m == null) {
+                        throw new NullPointerException("src[" + srcIdx + ']');
+                    }
+
+                    elements[dstIdx ++] = m;
+
+                    if (!(m instanceof ByteBuf)) {
                         byteBufsOnly = false;
                         break;
                     }
                 }
             }
 
+            for (; i < srcEndIdx; i ++) {
+                T m = src[srcIdx];
+                if (m == null) {
+                    throw new NullPointerException("src[" + srcIdx + ']');
+                }
+
+                elements[dstIdx ++] = m;
+            }
+        } finally {
+            if (dstIdx != newSize) {
+                // Could not finish iteration.
+                Arrays.fill(elements, size, dstIdx, null);
+            }
+        }
+
+        assert dstIdx == newSize;
+        size = newSize;
+
         return this;
     }
 
@@ -413,6 +443,23 @@ public final class MessageList<T> implements Iterable<T> {
         return new MessageListIterator();
     }
 
+    /**
+     * Returns the backing array of this list.  Use this array when you want to iterate over the list fast:
+     * <pre>
+     * {@link MessageList} list = ...;
+     * for (Object m: list.array()) {
+     *     if (m == null) {
+     *         break;
+     *     }
+     *
+     *     handleMessage(m);
+     * }
+     * </pre>
+     */
+    public T[] array() {
+        return elements;
+    }
+
     /**
      * Returns {@code true} if all messages contained in this {@link MessageList} are assignment-compatible with the
      * object represented by this {@link Class}.
@@ -474,18 +521,6 @@ public final class MessageList<T> implements Iterable<T> {
         }
     }
 
-    private void checkElements(T[] src, int srcIdx, int srcLen) {
-        if (src == null) {
-            throw new NullPointerException("src");
-        }
-        int end = srcIdx + srcLen;
-        for (int i = srcIdx; i < end; i ++) {
-            if (src[i] == null) {
-                throw new NullPointerException("src[" + i + ']');
-            }
-        }
-    }
-
     private final class MessageListIterator implements Iterator<T> {
         private int index;
         private int expectedModifications = modifications;