code: public void sessionHeartbeat(long sessionId) {
      synchronized (mSessions) {
        if (mSessions.containsKey(sessionId)) {
          mSessions.get(sessionId).heartbeat();
        } else {
          int sessionTimeoutMs = (int) ServerConfiguration
              .getMs(PropertyKey.WORKER_SESSION_TIMEOUT_MS);
          mSessions.put(sessionId, new SessionInfo(sessionId, sessionTimeoutMs));
        }
      }
    }
docs: Performs session heartbeat.
  
  @param sessionId the id of the session