[#1369] Move ImmediateEventExecutor to common and let it access via a static

* Also fix a bug there to return a correct implementation of ProgressivPRomi
  ImmediateEventExecutor

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

@@ -15,15 +15,17 @@
  */
 package io.netty.util.concurrent;
 
-import io.netty.util.concurrent.AbstractEventExecutor;
-import io.netty.util.concurrent.DefaultPromise;
-import io.netty.util.concurrent.EventExecutor;
-import io.netty.util.concurrent.EventExecutorGroup;
-import io.netty.util.concurrent.Promise;
-
 import java.util.concurrent.TimeUnit;
 
-final class ImmediateEventExecutor extends AbstractEventExecutor {
+/**
+ * {@link AbstractEventExecutor} which execute tasks in the callers thread.
+ */
+public final class ImmediateEventExecutor extends AbstractEventExecutor {
+    public static final ImmediateEventExecutor INSTANCE = new ImmediateEventExecutor();
+
+    private  ImmediateEventExecutor() {
+        // use static instance
+    }
 
     @Override
     public EventExecutorGroup parent() {
@@ -80,6 +82,11 @@ final class ImmediateEventExecutor extends AbstractEventExecutor {
         return new ImmediatePromise<V>(this);
     }
 
+    @Override
+    public <V> ProgressivePromise<V> newProgressivePromise() {
+        return new ImmediateProgressivePromise<V>(this);
+    }
+
     static class ImmediatePromise<V> extends DefaultPromise<V> {
         ImmediatePromise(EventExecutor executor) {
             super(executor);
@@ -90,4 +97,15 @@ final class ImmediateEventExecutor extends AbstractEventExecutor {
             // No check
         }
     }
+
+    static class ImmediateProgressivePromise<V> extends DefaultProgressivePromise<V> {
+        ImmediateProgressivePromise(EventExecutor executor) {
+            super(executor);
+        }
+
+        @Override
+        protected void checkDeadLock() {
+            // No check
+        }
+    }
 }

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

@@ -29,6 +29,9 @@ public final class ImmediateExecutor implements Executor {
 
     @Override
     public void execute(Runnable command) {
+        if (command == null) {
+            throw new NullPointerException("command");
+        }
         command.run();
     }
 }

transport/src/main/java/io/netty/channel/group/DefaultChannelGroup.java

@@ -22,6 +22,7 @@ import io.netty.channel.ChannelFutureListener;
 import io.netty.channel.FileRegion;
 import io.netty.channel.ServerChannel;
 import io.netty.util.concurrent.EventExecutor;
+import io.netty.util.concurrent.ImmediateEventExecutor;
 import io.netty.util.internal.PlatformDependent;
 
 import java.util.AbstractSet;
@@ -39,7 +40,6 @@ import java.util.concurrent.atomic.AtomicInteger;
 public class DefaultChannelGroup extends AbstractSet<Channel> implements ChannelGroup {
 
     private static final AtomicInteger nextId = new AtomicInteger();
-    private static final ImmediateEventExecutor DEFAULT_EXECUTOR = new ImmediateEventExecutor();
     private final String name;
     private final EventExecutor executor;
     private final ConcurrentMap<Integer, Channel> serverChannels = PlatformDependent.newConcurrentHashMap();
@@ -72,7 +72,7 @@ public class DefaultChannelGroup extends AbstractSet<Channel> implements Channel
      * is done against group names.
      */
     public DefaultChannelGroup(String name) {
-        this(name, DEFAULT_EXECUTOR);
+        this(name, ImmediateEventExecutor.INSTANCE);
     }
 
     /**

transport/src/main/java/io/netty/channel/group/DefaultChannelGroupFuture.java

@@ -23,6 +23,7 @@ import io.netty.util.concurrent.DefaultPromise;
 import io.netty.util.concurrent.EventExecutor;
 import io.netty.util.concurrent.Future;
 import io.netty.util.concurrent.GenericFutureListener;
+import io.netty.util.concurrent.ImmediateEventExecutor;
 
 import java.util.ArrayList;
 import java.util.Collection;