Use constant and cancel shutdown task

Fixes #194

Author: acogoluegnes

src/main/java/com/rabbitmq/client/impl/ChannelManager.java

@@ -52,7 +52,7 @@ public class ChannelManager {
     private ExecutorService shutdownExecutor;
     private final ThreadFactory threadFactory;
 
-    private int channelShutdownTimeout = (int) ((ConnectionFactory.DEFAULT_HEARTBEAT * 1.05) * 1000);
+    private int channelShutdownTimeout = (int) ((ConnectionFactory.DEFAULT_HEARTBEAT * AMQConnection.CHANNEL_SHUTDOWN_TIMEOUT_MULTIPLIER) * 1000);
 
     protected final MetricsCollector metricsCollector;
 

src/main/java/com/rabbitmq/client/impl/SocketFrameHandler.java

@@ -175,15 +175,18 @@ public Void call() throws Exception {
                 return null;
             }
         };
+        Future<Void> flushTask = null;
         try {
             if(this._shutdownExecutor == null) {
                 flushCallable.call();
             } else {
-                Future<Void> flushTask = this._shutdownExecutor.submit(flushCallable);
+                flushTask = this._shutdownExecutor.submit(flushCallable);
                 flushTask.get(SOCKET_CLOSING_TIMEOUT, TimeUnit.SECONDS);
             }
         } catch(Exception e) {
-
+            if(flushTask != null) {
+                flushTask.cancel(true);
+            }
         }
         try { _socket.close();                                   } catch (Exception _e) {}
     }