diff -r 3e9f26404433 -r c9c974817d0c src/goodjava/webserver/ServerSentEvents.java
--- a/src/goodjava/webserver/ServerSentEvents.java	Thu Nov 03 19:32:03 2022 -0600
+++ b/src/goodjava/webserver/ServerSentEvents.java	Thu Nov 03 22:05:11 2022 -0600
@@ -11,9 +11,14 @@
 import java.util.HashMap;
 import java.util.Collections;
 import java.util.Iterator;
+import java.util.Timer;
+import java.util.TimerTask;
+import goodjava.logging.Logger;
+import goodjava.logging.LoggerFactory;
 
 
 public class ServerSentEvents {
+	private static final Logger logger = LoggerFactory.getLogger(ServerSentEvents.class);
 
 	private static class Con {
 		final Socket socket;
@@ -45,8 +50,10 @@
 					iter.remove();
 				}
 			}
-			if( cons.isEmpty() )
+			if( cons.isEmpty() ) {
 				map.remove(url);
+				//logger.info("removed "+url);
+			}
 		}
 	}
 
@@ -92,5 +99,26 @@
 		write( url, toData(message) );
 	}
 
+	private static void sweep() {
+		List<String> urls;
+		synchronized(map) {
+			urls = new ArrayList<String>(map.keySet());
+		}
+		for( String url : urls ) {
+			write( url, "event: ping\n" );
+		}
+	}
+
+	private static final Timer sweeper = new Timer("ServerSentEvents",true);
+	static {
+		long period = 1000L*60*60;  // hour
+		TimerTask task = new TimerTask() {
+			public void run() {
+				sweep();
+			}
+		};
+		sweeper.schedule(task,period,period);
+	}
+
 	private ServerSentEvents() {}  // never
 }