Fixed @tommi27 synchronization frenzy for sensors

I have now discovered the Schadenfreude in using git-blame. To quote an
old commit message from high school:
[Trascrizione domande fisica e correzione di GRAVISSIMI bug presenti nel
codici di Maggioni](dd0933def0)
```
La trascrizione dei test è stata fatta in modo certosino, simile a
quello dei monaci emanuensi.
I GRAVISSIMI buggg (3 g perchè fa faigo) potevano rendere il sito
incomprensibile
```

src/main/java/ch/usi/inf/sa4/sanmarinoes/smarthut/socket/SensorSocketEndpoint.java

@@ -8,6 +8,8 @@ import com.google.common.collect.HashMultimap;
 import com.google.common.collect.Multimap;
 import com.google.common.collect.Multimaps;
 import com.google.gson.Gson;
+
+import java.io.IOException;
 import java.util.*;
 import javax.websocket.*;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -57,20 +59,30 @@ public class SensorSocketEndpoint extends Endpoint {
      * @param u the user to which to send the message
      * @return number of successful transfer
      */
-    public long broadcast(Object message, User u) {
+    public void broadcast(Object message, User u) {
         final HashSet<Session> sessions = new HashSet<>(authorizedClients.get(u));
 
-        return sessions.stream()
+
+
+        sessions.stream()
                 .filter(
                         s -> {
                             if (s.isOpen()) return true;
                             sessions.remove(s);
                             return false;
                         })
-                .filter(didThrow(s -> s.getBasicRemote().sendText(gson.toJson(message))))
-                .count();
+                .forEach(s -> {
+                    synchronized (this){
+                        try {
+                            s.getBasicRemote().sendText(gson.toJson(message));
+                        } catch (IOException e) {
+                            e.printStackTrace();
+                        }
+                    }
+                });
     }
 
+
     /**
      * Handles the opening of a socket session with a client
      *