Use bitwise operations to choose next EventExecutor if number of EventExecutors is power of two

Author: Norman Maurer

common/src/main/java/io/netty/util/concurrent/MultithreadEventExecutorGroup.java

@@ -34,6 +34,7 @@ public abstract class MultithreadEventExecutorGroup extends AbstractEventExecuto
     private final AtomicInteger childIndex = new AtomicInteger();
     private final AtomicInteger terminatedChildren = new AtomicInteger();
     private final Promise<?> terminationFuture = new DefaultPromise(GlobalEventExecutor.INSTANCE);
+    private final EventExecutorChooser chooser;
 
     /**
      * Create a new instance.
@@ -63,6 +64,12 @@ protected MultithreadEventExecutorGroup(int nThreads, Executor executor, Object.
         }
 
         children = new EventExecutor[nThreads];
+        if (isPowerOfTwo(children.length)) {
+            chooser = new PowerOfTwoEventExecutorChooser();
+        } else {
+            chooser = new GenericEventExecutorChooser();
+        }
+
         for (int i = 0; i < nThreads; i ++) {
             boolean success = false;
             try {
@@ -116,7 +123,7 @@ protected ThreadFactory newDefaultThreadFactory() {
 
     @Override
     public EventExecutor next() {
-        return children[Math.abs(childIndex.getAndIncrement() % children.length)];
+        return chooser.next();
     }
 
     /**
@@ -208,4 +215,26 @@ public boolean awaitTermination(long timeout, TimeUnit unit)
         }
         return isTerminated();
     }
+
+    private static boolean isPowerOfTwo(int val) {
+        return (val & -val) == val;
+    }
+
+    private interface EventExecutorChooser {
+        EventExecutor next();
+    }
+
+    private final class PowerOfTwoEventExecutorChooser implements EventExecutorChooser {
+        @Override
+        public EventExecutor next() {
+            return children[childIndex.getAndIncrement() & children.length - 1];
+        }
+    }
+
+    private final class GenericEventExecutorChooser implements EventExecutorChooser {
+        @Override
+        public EventExecutor next() {
+            return children[Math.abs(childIndex.getAndIncrement() % children.length)];
+        }
+    }
 }