code: public synchronized boolean enableListener(boolean enable) {
          boolean success = true;
          if (enable && eventSource == null) {
              success = initEventSource();
          }
          bEnableListener = enable;
          if (tc.isDebugEnabled()) {
              Tr.debug(tc, "enableListener() cacheName=" + this.cacheName + " enable=" + enable + " success=" + success
                      + " ignoreValueInInvalidationEvent=" + this.ignoreValueInInvalidationEvent);
          }
          return success;
      }
docs: enableListener - enable or disable the invalidation, change and preInvalidation listener support. You must call
  enableListener(true) before calling addInvalidationListner(), addChangeListener() or
  addPreInvalidationListener().
  
  @param enable
  - true to enable support for invalidation, change and preInvalidation listeners or false to disable
  support for invalidation, change and preInvalidation listeners
  @return boolean "true" means listener support was successfully enabled or disabled. "false" means this cache is
  configurated to use the listener's J2EE context for event notification and the callback registration
  failed. In this case, the caller's thread context will be used for event notification.