code: public final synchronized void shutdown() {
          if (DESTROYED_UPDATER.compareAndSet(this, 0, 1)) {
              engineMap.remove(ssl);
              SSL.freeSSL(ssl);
              ssl = networkBIO = 0;
  
              isInboundDone = outboundClosed = true;
          }
  
          // On shutdown clear all errors
          SSL.clearError();
      }
docs: Destroys this engine.