Add shutdown hook for WebSphere and checkError() to detect disconnect…

…ed client (issue Netflix#346)

WebSphere won't shutdown a servlet until after a 60 second timeout if
there is an  instance of the servlet executing a request.  Add a
shutdown method to enable a hook to notify Hystrix to shutdown.  You
must invoke this method at app server shutdown, perhaps from another
servlet's destroy() method.

Also added explicit checkError() in poller loop to check for
disconnected client.

hystrix-contrib/hystrix-metrics-event-stream/src/main/java/com/netflix/hystrix/contrib/metrics/eventstream/HystrixMetricsStreamServlet.java

@@ -63,7 +63,21 @@ public class HystrixMetricsStreamServlet extends HttpServlet {
     private static AtomicInteger concurrentConnections = new AtomicInteger(0);
     private static DynamicIntProperty maxConcurrentConnections = DynamicPropertyFactory.getInstance().getIntProperty("hystrix.stream.maxConcurrentConnections", 5);
 
-    private volatile boolean isDestroyed = false;
+    private static volatile boolean isDestroyed = false;
+
+    /**
+     * WebSphere won't shutdown a servlet until after a 60 second timeout if there is an instance of the servlet executing 
+     * a request.  Add this method to enable a hook to notify Hystrix to shutdown.  You must invoke this method at
+     * shutdown, perhaps from some other serverlet's destroy() method.
+     */
+    public static void shutdown() {
+    	isDestroyed = true;
+    }
+
+    @Override 
+    public void init() throws ServletException {
+    	isDestroyed = false;
+    }
 
     /**
      * Handle incoming GETs
@@ -146,6 +160,11 @@ private void handleRequest(HttpServletRequest request, HttpServletResponse respo
                         // after outputting all the messages we will flush the stream
                         response.flushBuffer();
 
+                        // explicitly check for client disconnect - PrintWriter does not throw exceptions
+                        if (response.getWriter().checkError()) {
+                        	throw new IOException("io error");
+                        }
+
                         // now wait the 'delay' time
                         Thread.sleep(delay);
                     }